Peripheral deiodinase activity: A potential explanation for the association between maternal weight and gestational hyperglycemia

Background

High maternal weight is known to associate with both low free thyroxine and gestational diabetes mellitus. We explore a deiodinase-related mechanism that may help explain these associations.

Methods

Among 108 women receiving routine oral glucose tolerance testing for gestational diabetes mellitus, we collected biophysical data and measured free thyroxine and total triiodothyronine, using residual plasma samples.

Results

Fasting triiodothyronine/free thyroxine ratio and triiodothyronine were higher among women with gestational diabetes mellitus (p = 0.02; p = 0.04). The triiodothyronine/free thyroxine ratio and triiodothyronine measurements at 2 h were associated with weight (r = 0.20, p = 0.04; r = 0.22, p = 0.02); free thyroxine showed a non-significant inverse weight relationship (r = -0.06, p = 0.55). Glucose at all four intervals was associated with triiodothyronine/free thyroxine ratios, and triiodothyronine at 2 h. In stepwise regression, triiodothyronine/free thyroxine ratio predicted glucose more strongly than did weight.

Conclusion

These relationships may be explained by higher maternal weight inducing peripheral deiodinase activity, resulting in higher plasma glucose (via triiodothyronine stimulation) and thereby increasing gestational diabetes mellitus risk.

Clinical validation of a new dimeric inhibin-A assay suitable for second trimester Down's syndrome screening

Objective To compare the Down's syndrome screening performance of a simplified dimeric inhibin-A assay (Diagnostic Systems Laboratories (DSL)) with an assay whose clinical utility has been established (Serotec).

Setting A case control set consisting of 51 Down's syndrome and 245 matched unaffected pregnancies collected as part of an earlier multicentre cohort study.

Methods Sera were assayed for dimeric inhibin-A using the DSL assay and Serotec reference assay. Data analysis included a method comparison of mass values, fit of data to a logarithmic Gaussian distribution, and determination of detection and false positive rates. In addition, 234 fresh sera were assayed using the simplified method.

Results The two assays showed a high correlation (r =0.93) but average concentrations of the DSL assay were 48% higher. However, the differences were basically proportional over the range of values important for screening. The detection rate was essentially equivalent for the DSL assay whether analysed univariately or in combination with other markers (for example, 79% v 75% at a 5% false positive rate for the DSL and Serotec assays for the combination of α fetoprotein, unconjugated oestriol, human chorionic gonadotrophin, and dimeric inhibin-A, respectively). The 234 dimeric inhibin-A values measured on fresh sera fitted a logarithm Gaussian distribution for the DSL assay, as indicated by the fit to a probability plot.

Conclusions The Down's syndrome screening performance of a simplified dimeric inhibin-A immunoassay was equivalent to a more labour intensive established dimeric inhibin-A assay.

Measuring maternal serum screening markers for Down's syndrome in plasma collected for cell-free DNA testing

Objectives To determine whether maternal plasma collected in cell-free DNA stabilizing tubes is suitable for measuring prenatal screening 'serum' markers. Methods Matched plasma and serum samples were collected from 41 second trimester and 42 first trimester non-Down's syndrome pregnancies. Second trimester samples were tested for alpha-fetoprotein, unconjugated estriol, human chorionic gonadotropin, and inhibin-A (Beckman Coulter DxI immunoassay). First trimester samples were tested for human chorionic gonadotropin and pregnancy-associated plasma protein A. Method comparisons performed for each marker compared plasma and serum results. Down's syndrome likelihood ratios in serum and plasma were compared. Results Plasma and serum results for all markers were highly correlated ( r > 0.983) but for all, plasma results differed, usually by proportional amounts. After conversion to multiples of the median using sample type-specific medians, the logarithmic standard deviations in serum and plasma did not differ (all p > 0.37). Likelihood ratios for the first and second trimester marker combinations were highly correlated and closely agreed (log likelihood ratios range 1.005 to 1.032; 1.000 indicates complete agreement). Conclusions These results using specialized plasma collection tubes are similar to those of our earlier study showing that plasma collected in EDTA tubes is suitable for 'serum' Down's syndrome screening. Laboratories must account for proportional changes by computing new plasma medians or modifying existing serum medians. Using a portion of the plasma from cell-free DNA collection tubes for 'serum screening' may have an advantage in programmes that are reflexively testing cell-free DNA, as only one sample type need be collected.

Free Thyroxine During Early Pregnancy and Risk for Gestational Diabetes

Several studies have now reported associations between gestational diabetes mellitus (GDM) and low free thyroxine (fT4) during the second and third trimesters, but not in the first trimester. The present study further examines relationships between low fT4, maternal weight, and GDM among women in the FaSTER (First and Second Trimester Evaluation of Risk) trial, in an effort to determine the extent to which thyroid hormones might contribute to causality. The FaSTER cohort includes 9351 singleton, euthyroid women; 272 of these women were subsequently classified as having GDM. Thyrotropin (TSH), fT4, and thyroid antibodies were measured at 11–14 weeks’ gestation (first trimester) and 15–18.9 weeks’ gestation (second trimester). An earlier report of this cohort documented an inverse relationship between fT4 in the second trimester and maternal weight. In the current analysis, women with GDM were significantly older (32 vs. 28 years) and weighed more (75 vs. 64.5 kg). Maternal weight and age (but not TSH) were significantly associated univariately with fT4 (dependent variable), in the order listed. Second trimester fT4 odds ratios (OR) for GDM were 2.06 [95% CI 1.37–3.09] (unadjusted); and 1.89 [95% CI 1.26–2.84] (adjusted). First trimester odds ratios were not significant: OR 1.45 [95%CI 0.97–2.16] (unadjusted) and 1.11 [95% CI 0.74–1.62] (adjusted). The second trimester fT4/GDM relationship thus appeared to strengthen as gestation progressed. In FaSTER, high maternal weight was associated with both low fT4 and a higher GDM rate in the second trimester. Peripheral deiodinase activity is known to increase with high caloric intake (represented by high weight). We speculate that weight-related low fT4 (the metabolically inactive prohormone) is a marker for deiodinase activity, serving as a substrate for conversion of fT4 to free triiodothyronine (fT3), the active hormone responsible for glucose-related metabolic activity.

An Inverse Relationship Between Weight and Free Thyroxine During Early Gestation Among Women Treated for Hypothyroidism

BACKGROUND

Following treatment sufficient to normalize thyrotropin (TSH), nonpregnant hypothyroid adults display higher free thyroxine (FT(4)) concentrations than a reference population. Our aim is to determine whether FT(4) concentrations are higher during pregnancy among women treated for hypothyroidism and whether their weight is associated with FT(4) levels. Weight/FT(4) relationships have not previously been reported in treated hypothyroid adults (either pregnant or nonpregnant).

METHODS

Thyroid-related measurements were available from over 10,000 women at two early pregnancy time periods from the FaSTER (First and Second Trimester Evaluation of Risk for Fetal aneuploidy) trial (1999-2002). All women were receiving routine prenatal care. Present analyses were restricted to 9267 reference women and 306 treated, hypothyroid women with TSH between the 2nd and 98th reference percentiles. We compared FT(4) values between those groups at 11-14 and 15-18 weeks' gestation, using linear regression to estimate FT(4)/maternal weight relationships, after accounting for treatment and other potential covariates.

RESULTS

In comparison to reference women, median FT(4) values and percent of FT(4) values ≥95th reference percentile were significantly higher in treated women at both 11-14 and 15-18 weeks' gestation (p<0.001) overall and after stratification by weight into tertiles. Among both treated and reference women, median FT(4) decreased monotonically with increasing weight, regardless of anti-thyroperoxidase antibody status. Maternal age, maternal weight, and treatment status were important predictors of FT(4) levels (p<0.001, defined by partial r(2) values of 1% or higher). Anti-thyroperoxidase antibody status, TSH values (after logarithmic transformation), and all interaction terms were well below an r(2) of 1%. FT(4) levels were 1.45 pmol/L higher in treated than reference women, independent of other factors. Maternal age and weight reduced FT(4) levels by 0.0694 pmol/L/y and 0.0208 pmol/L/kg, respectively.

CONCLUSIONS

FT(4) concentrations are higher among treated hypothyroid pregnant women than among reference women, and higher maternal weight is associated with lower FT(4) levels, regardless of treatment status. This inverse relationship is not associated with higher TSH levels. While no immediate clinical implications are attached to the current observations, increased peripheral deiodinase activity in the presence of higher weight might explain these findings. Further investigation appears worthy of attention.

Evaluating first trimester maternal serum screening combinations for Down syndrome suitable for use with reflexive secondary screening via sequencing of cell free DNA: high detection with low rates of invasive procedures

OBJECTIVES

Examine primary Down syndrome screening using combinations of first trimester serum markers, with and without sequencing of cell free DNA as a secondary reflexive test.

METHODS

Samples from 40 Down syndrome cases were matched with five control samples and tested for PAPP-A, free β, AFP, inhibin-A and PlGF. Results were converted to weight-adjusted multiples of the median (MoM) and population parameters computed. Monte Carlo simulation modeled Down syndrome detection and false positive rates for various marker combinations. After reflexive DNA testing, the revised detection and false positive rates were also computed.

RESULTS

At a primary false positive rate of 20%, the baseline combination (maternal age, PAPP-A and free β) detected 86.9%. Adding AFP or PlGF increased detection to 89.8% and 89.5%, respectively. Adding AFP and PlGF, AFP and inhibin-A, or all three markers, detected 93.7%, 94.1% and 95.5%, respectively. Modeling reflexive cf DNA testing results in little loss in detection (1%), but false positive rates fall to 0.2%.

CONCLUSION

First trimester reflexive testing does not require nuchal translucency measurements, and has high detection and very low rates of invasive procedures. However, timing of DNA sample collection and the costs of sample collection and DNA testing need to be considered before implementation.

Implications of High Free Thyroxine (FT4) concentrations in euthyroid pregnancies: the FaSTER trial

CONTEXT

Lower birth weight has been reported in conjunction with high maternal free T4 (FT4) in euthyroid pregnancies, raising concerns for suboptimal outcomes.

OBJECTIVE

The objective of the study was to explore the relationships between high maternal FT4 and pregnancy complications in euthyroid women and to further examine the relationships among maternal size, FT4, and birth weight.

DESIGN

This was an observational multicenter cohort study.

SETTING

The study was conducted at prenatal clinics.

STUDY SUBJECTS

A total of 9209 euthyroid women with singleton pregnancies participated in the study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

Relationships between second-trimester high maternal FT4 and pregnancy/delivery complications and, among FT4, maternal weight and birth weight were measured.

RESULTS

Women in the highest FT4 quintile are younger and weigh less than women in quintiles 1-4; gestational diabetes and preeclampsia occur less often (P = < .001, P < .001, P < .001, and P = .05, respectively). Lowest median birth weight occurs among women in the highest FT4 quintile (P = < .001), but deliveries less than 37 weeks' gestation are not increased. Labor/delivery complications do not differ by FT4 quintile. Restricting analyses to maternal weight-adjusted small-for-gestational-age deliveries yields similar results, except for preeclampsia. In the highest maternal weight decile, adjusted median birth weight is 266 g higher (8.3%) than in the lowest weight decile; adjusted median FT4 is 0.91 pmol/L lower (6.8%). Among women in the highest FT4 decile, adjusted median birth weight is 46 g lower (1.3%) than in the lowest FT4 decile. All three relationships are statistically significant (P < .001, P < .001, and P = .004, respectively).

CONCLUSIONS

Lower median birth weight among euthyroid women with high FT4 is not associated with adverse pregnancy outcomes. Further investigation is indicated to determine how the variations in thyroid hormone concentration influence birth weight.

Maternal Body Mass Index during Pregnancy and Offspring Neurocognitive Development

BACKGROUND

This hypothesis generating study explores second trimester maternal body mass index (BMI) during pregnancy and offspring neurocognitive development.

METHODS

Mothers and offspring served as controls in two earlier studies: 101 children at age two years and 118 children at age eight years.

RESULTS

Frequency of maternal BMI ≥30 kg/m² increased from 10% in 1987-1990 to 30% in 2004-2006 (P < 0.001); the socioeconomic gradient became more pronounced. At age two, one or more BSID-III (Bayley Scales of Infant Development, 3rd Edition) scores <85 were more frequent with higher maternal BMI (P = 0.029); regression analysis suggested an inverse relationship between language scores and BMI (P = 0.054). Among eight-year-olds, one or more WISC-III (Wechsler Intelligence Scale for Children, 3rd edition) scores <85 increased with maternal BMI (P = 0.017); regression analysis showed an inverse relationship between performance subscale IQ score and BMI (P = 0.023).

CONCLUSION

Second trimester maternal obesity may be an independent risk factor for some aspects of children's neurocognitive development. Further study is indicated.

Impact of adjusting for the reciprocal relationship between maternal weight and free thyroxine during early pregnancy

BACKGROUND

Among euthyroid pregnant women in a large clinical trial, free thyroxine (FT4) measurements below the 2.5th centile were associated with a 17 lb higher weight (2.9 kg/m(2)) than in the overall study population. We explore this relationship further.

METHODS

Among 9351 women with second trimester thyrotropin (TSH) measurements between 1st and 98th centiles, we examine: (i) the weight/FT4 relationship; (ii) percentages of women in three weight categories at each FT4 decile; (iii) FT4 concentrations in three weight categories at each TSH decile; and (iv) impact of adjusting FT4 for weight--in the reference group and in 190 additional women with elevated TSH measurements.

RESULTS

FT4 values decrease steadily as weight increases (p<0.0001 by ANOVA) among women in the reference group (TSH 0.05-3.8 IU/L). TSH follows no consistent pattern with weight. When stratified into weight tertiles, 48% of women at the lowest FT4 decile are heavy; the percentage decreases steadily to 22% at the highest FT4 decile. Median FT4 is lowest in heaviest women regardless of the TSH level. In the reference group, weight adjustment reduces overall variance by 2.9%. Fewer FT4 measurements are at either extreme (below the 5th FT4 centile: 4.8% before adjustment, 4.7% after adjustment; above the 95th FT4 centile: 5.0% and 4.7%, respectively). Adjustment places more light weight women and fewer heavy women below the 5th FT4 centile; the converse above the 95th centile. Between TSH 3.8 and 5 IU/L, the FT4 percentage below the 5th FT4 centile is not elevated (3.8% before adjustment, 3.1% after adjustment). Percentage of FT4 values above the 95th centile, however, is lower (1.5% before adjustment, 0.8% after adjustment). Above TSH 5 IU/L, 25% of women have FT4 values below the 5th FT4 centile; weight adjustment raises this to 30%; no FT4 values remain above the 95th FT4 centile.

CONCLUSIONS

During early pregnancy, TSH values are not associated with weight, unlike nonpregnant adults. Lower average FT4 values among heavy women at all TSH deciles partially explain interindividual differences in FT4 reference ranges. The continuous reciprocal relationship between weight and FT4 explains lower FT4 with higher weight. Weight adjustment refines FT4 interpretation.

Feasibility of Using Plasma Rather Than Serum in First and Second Trimester Multiple Marker Down's Syndrome Screening

Objective

To compare maternal plasma with serum for measuring markers currently used in first and second trimester screening for Down's syndrome.

Setting

A laboratory-based investigation of two sample types in assays used in prenatal screening for Down's syndrome.

Methods

A paired data-set included both plasma and serum from 101 pregnant women. A nested case/control data-set included only plasma samples from 34 first and 23 second trimester Down's syndrome pregnancies, each matched with six euploid controls. Analyte levels were measured and converted to multiples of the median (MoM).

Results

In the paired data-set, each of the five analytes (alphafetoprotein, unconjugated estriol, human chorionic gonadotropin, inhibin-A and pregnancy-associated plasma protein A) in serum and plasma was highly correlated (r > 0.970) and after conversion to MoM, the resulting distributions were equivalent ( P > 0.7). In the matched data-set, plasma-based median MoM levels in cases were consistent with the published serum counterparts for all markers.

Conclusions

This study provides strong evidence that current serum-based prenatal screening can be performed equally well using plasma samples. This may prove useful, especially if secondary screening using a DNA-based test requires maternal plasma.

Mid-gestational maternal free thyroxine concentration and offspring neurocognitive development at age two years

CONTEXT

Lower neurocognitive development scores at age 2 yr have been reported in association with euthyroid hypothyroxinemia during early pregnancy.

OBJECTIVE

The objective of this study was to further explore this association with euthyroid hypothyroxinemia during early pregnancy.

DESIGN

This was an observational, nested case-control study.

SETTING

The study was conducted at physician offices and prenatal clinics throughout Maine.

STUDY SUBJECTS

Between May 2004 and March 2006, TSH was measured in 5734 women in conjunction with second-trimester Down syndrome screening. After completion of pregnancy, free T(4) was measured in stored second-trimester sera from euthyroid women (TSH 0.1-3.5 mIU/ml; n = 5560). Women with free T(4) at the third centile or less (n = 99) were matched with women whose free T(4) was at the 10th to the 90th centile (n = 99).

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Bayley Scales of Infant Development (BSID III) were administered to the 198 offspring at age 2 yr. Scores for cognitive, language, and motor development were compared between matched pairs of offspring from the two groups before and after correcting for relevant variables.

RESULTS

Unadjusted BSID-III scores (cognitive, language, and motor) were lower by about 3% at age 2 yr among offspring of 98 hypothyroxinemic women (cases), reaching borderline significance for cognitive and motor scores. After adjustment for gestational age, the child's age at testing, maternal weight, and education, all differences diminished and became nonsignificant. Scores less than 85 were more frequent among case children but did not reach statistical significance (P = 0.14).

CONCLUSIONS

Isolated hypothyroxinemia during the second trimester is not associated with significantly lower BSID-III scores at age 2 yr, compared with scores for offspring of matched euthyroxinemic women.

The relationship between PTH and 25-hydroxy vitamin D early in pregnancy

OBJECTIVE

Measure serum PTH and 25(OH)D in a cross-sectional sample of pregnant women at 11th through 13th weeks' gestation to examine vitamin D status and consider implications.

DESIGN

Observational: we retrieved residual sera stored at -20 °C after routine first trimester Down's syndrome screening, distributed over 12 months.

PATIENTS

430 African American women and 586 Caucasian women.

MEASUREMENTS

PTH and 25-hydroxy vitamin D [25(OH)D] immunoassays.

RESULTS

PTH medians were: 1·33 pmol/l (African American women); 1·20 pmol/l (Caucasian women) (t = 0·43, P = 0·7). Concentrations were highest in winter and decreased significantly in spring, fall, and summer. There was a direct PTH/weight relationship in Caucasian (t = 3·12, P < 0·002), but not African American women (t = 1·34, P = 0·18). Median 25(OH)D concentrations were 47·5 nmol/l (African American women) and 65 nmol/l (Caucasian women) (t = 13·7, P < 0·001). Concentrations were lowest in winter and rose significantly in spring, fall, and summer. Reciprocal 25(OH)D/weight relationships existed for both racial groups (t =-4·31 P < 0·001; t = 4·54, P < 0·001, respectively). Among 68 Caucasian women who smoked, median PTH and 25(OH)D concentrations were somewhat lower (P = ns). In separate regression models with PTH and 25(OH)D [dependent variables] and season, weight and smoking [independent variables], the only qualifying interactive term was in the Caucasian PTH model (season*1/weight). A regression model applied to adjusted scatter plots of PTH vs 25(OH)D indicated a weak relationship.

CONCLUSIONS

The PTH/25(OH)D relationship is weaker during early pregnancy than in non-pregnant adults, making it unreliable for estimating vitamin D sufficiency. A suitable reference point for sufficiency might be the maternal 25(OH)D level considered sufficient for adequate transfer to neonates.

Estimating first-trimester combined screening performance for Down syndrome in dried blood spots versus fresh sera

PURPOSE

The study purpose was to examine the consequences of using dried blood spots rather than fresh sera in first-trimester Down syndrome screening.

METHODS

We collected and compared human chorionic gonadotropin and pregnancy-associated plasma protein-A results from clients providing dried blood spots (Cohort 1) and from other clients providing fresh sera (Cohort 2). Inclusion and exclusion criteria aimed at ensuring the two cohorts were similar.

RESULTS

The average concentrations of human chorionic gonadotropin and pregnancy-associated plasma protein-A are significantly different for the two cohorts. When the results are converted to multiples of the median and weight-adjusted, the variances for human chorionic gonadotropin and pregnancy-associated plasma protein-A in Cohort 1 are greater by 25% and 14%, respectively. Modeling the impact of this increased variance shows that Down syndrome detection is expected to be lower in Cohort 1 (83% vs. 85% at a 5% false-positive rate) or the false-positive rate is expected to be higher (3.9% vs. 3.0% at an 80% detection rate).

CONCLUSIONS

This study of two closely matched cohorts provides indirect evidence that dried blood spots will result in slightly lower Down syndrome screening performance. Studies should be undertaken to confirm and further quantify differences in assigned risks by a direct comparison using matched serum and dried blood spots collected from the same women.

Reference distributions for apolipoproteins AI and B and B/AI ratios: comparison of a large cohort to the world's literature

Limiting the clinical utility of apolipoproteins AI (apo AI) and B (apo B) and the apo B/AI ratios until the last decade has been the lack of satisfactory methods for quantifying serum levels and credible reference materials. Great technological strides have been made in the last few years. The remaining barrier to more relevant and cost-effective use of serum protein data for diagnosis and prognosis has been the availability of widely recognized reliable reference intervals from birth to old age for both males and females. A total of 82 publications reporting reference intervals have been identified that meet most of the same inclusion criteria used in our prior six studies. These have been analyzed statistically and compared to similar studies, i.e., sufficient number, listed subject criteria, method, and reference material, in general terms. Published smaller studies with constrained age ranges, agree on average with our large series of life-long reference intervals that range from less than one year to over 80 years. This study was performed to assess the degree of agreement between smaller reference interval studies to our large population analysis. This meta-analysis provides support and reassurance that many of the smaller reference intervals published previously fall within reasonable limits of out large population.

Hyperglycosylated-hCG (h-hCG) and Down syndrome screening in the first and second trimesters of pregnancy

OBJECTIVE

To validate Down syndrome screening protocols that include hyperglycosylated-hCG (h-hCG) measurements.

METHODS

Measuring h-hCG in 21 641 fresh first- and second-trimester maternal serum samples, but not for clinical interpretation. Nuchal translucency (NT) and pregnancy associated plasma protein-A (PAPP-A) measurements were available in the first trimester; alpha-fetoprotein (AFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) measurements in the second trimester.

RESULTS

Of the 23 first- and 26 second-trimester Down syndrome pregnancies identified, 52 and 65% of h-hCG measurements were above the 95th centile, respectively. At a 3% false positive rate, maternal age, NT, PAPP-A and h-hCG detected 78% of cases (95% CI, 56-93%). Other combinations were consistent with previous modeling utilizing stored samples. A literature summary indicates h-hCG is as strong a marker as free-beta between 10 and 13 weeks' gestation.

CONCLUSIONS

Down syndrome screening performance of h-hCG using fresh samples meets published expectations based on stored samples. h-hCG could replace free beta measurements, at gestational ages as early as 10 weeks.

Comparison of Serum Markers in First-Trimester Down Syndrome Screening

OBJECTIVE

To estimate patterns of total hCG and inhibin A levels in the late first trimester of Down syndrome pregnancies, compare them with that of free beta-hCG, and assess screening performance of these markers individually and in combination with pregnancy-associated plasma protein-A (PAPP-A) and nuchal translucency.

METHODS

Seventy-nine matched case-control sets of maternal serum samples (each Down syndrome case matched to 5 controls) from 11 through 13 completed weeks of gestation were taken from the sample bank of the First and Second Trimester Evaluation of Risk Consortium, a population-based study, and assayed for levels of free beta-hCG, total hCG, and inhibin A. Distribution characteristics and correlations of the multiples of the median values were estimated in cases and controls. Screening performance for each marker, alone and in combination with PAPP-A, nuchal translucency, and maternal age, was calculated.

RESULTS

Median multiples of the median levels of free beta-hCG, total hCG, and inhibin A in cases were more elevated as gestation increased from 11 to 13 weeks, with univariate detection rates of 31%, 23%, and 29%, respectively, at a 5% false-positive rate. At 12 weeks, the multivariate detection rates at a 5% false-positive rate for nuchal translucency and PAPP-A (with maternal age) with either free beta-hCG, total hCG, or inhibin A were 84%, 83%, and 85%, respectively. The improvement in performance from nuchal translucency and PAPP-A to any of the three-marker tests was significant, while performance of any of the three-marker combinations was not significantly different from each other.

CONCLUSION

Although levels of free beta-hCG in affected pregnancies were higher earlier than the levels of either total hCG or inhibin A, there was no significant difference in screening performance when either of the three markers was used with nuchal translucency and PAPP-A at 11-13 weeks of pregnancy.

LEVEL OF EVIDENCE

II-2.

Repeated measurement of pregnancy-associated plasma protein-A (PAPP-A) in Down syndrome screening: A validation study

OBJECTIVES

To confirm that measuring pregnancy-associated plasma protein-A (PAPP-A) in both first- and second-trimester serum samples improves Down syndrome screening.

METHODS

We selected paired first- and second-trimester stored serum samples from 34 Down syndrome pregnancies (cases) and 514 unaffected pregnancies (controls) and tested the second-trimester samples for PAPP-A and dimeric inhibin-A (DIA). First-trimester PAPP-A measurements were already available, as were second-trimester measurements of alpha-fetoprotein, unconjugated estriol (uE3), and human chorionic gonadotrophin (hCG).

RESULTS

PAPP-A was lower among cases than controls (0.47 MoM) in the first trimester (at an average of 12.5 weeks); in the second trimester, it was not different (0.91 MoM). Using repeated measures of PAPP-A alone, 21 of 34 cases were detected (62%, 95%CI 44% to 78%) with 5% false positives. At an observed 2% false-positive rate, the detection rates (DR) for the quadruple (69%) and serum integrated (69%) tests were lower than for the repeated measures test (75%). Modelled performance at 12 weeks was similar to these observed findings (70, 75, and 82%, respectively). If the first-trimester samples were collected at 10 weeks, however, DR would be higher (70, 81, and 91%, respectively).

CONCLUSIONS

Adding a repeated measure of PAPP-A to existing serum markers improves Down syndrome screening to levels that are currently obtainable only by including ultrasound measurement of nuchal translucency (NT). Serum-based screening has the advantages of higher availability and reliability at a lower cost, resulting in a more effective screening strategy. A serum-based repeated measures test has a place in routine Down syndrome screening.

Reference distributions for apolipoproteins AI and B and the apolipoprotein B/AI ratios: a practical and clinically relevant approach in a large cohort

The two serum apolipoproteins in the highest concentrations, apolipoprotein (apo) AI and apolipoprotein B, and the apolipoprotein B/AI ratio are measured to assess clinical risk for atherosclerotic heart and peripheral vascular diseases. The study is based on a cohort of over 37,000 Caucasian individuals from northern New England measured in one laboratory by immunonephelometry using standardized reference materials. All samples received for protein analyses were accepted provided adequate identifying information was available. Laboratory and demographic information was entered into a single database for subsequent study. Our results show that for males without evidence of inflammation, values of apo AI change little through life. For females, however, values gradually increase until about 60 years of age then fall somewhat thereafter. Among adults, females have higher apo AI values on average, than males. Apo B values change significantly through life, increasing after the end of the second decade to a peak during the sixth decade, then falling thereafter. In the past, concern has been expressed that apo AI is an acute phase reactant (APR), thus complicating cardiovascular risk assessment. The effects of an APR (C-reactive protein >or=10 mg/L) on apo AI, but not on apo B, are measurable for both sexes, most noticeably beyond the age of 60 years in males and females. When values were expressed as age- and gender-specific multiples of the median (MoMs), the resulting distributions fit a log-Gaussian distribution well over a broad range. The size of the relatively homogenous cohort, by a standardized approach, provides a firm basis for comparison to preexisting reference intervals and for establishing a clinically useful and current reference interval for the three main apolipoprotein values.

Maternal Serum Invasive Trophoblast Antigen and First-Trimester Down Syndrome Screening

Background: In the United States, Down syndrome screening is still performed mainly in the second trimester, using 3 or 4 markers. Moving screening into the first trimester has the advantage of earlier diagnosis. Currently, first-trimester screening typically includes maternal serum pregnancy-associated plasma protein-A (PAPP-A), the free β-subunit of human chorionic gonadotropin (free β), and ultrasound measurement of nuchal translucency thickness (NT). The current report describes a case–control study of serum invasive trophoblast antigen (ITA) and its possible inclusion in first-trimester screening for Down syndrome.

Methods: As part of an earlier observational study, serum samples from 54 Down syndrome and 276 matched unaffected pregnancies were collected between 9 and 15 weeks of gestation. Samples had been aliquoted and stored at −20 °C for 8 years. ITA was measured and converted to weight-adjusted multiples of the median (MoM). The distributions of other first-trimester markers are from a single published study.

Results: Median ITA MoM in Down syndrome pregnancies increase as gestational age increases (2.02 MoM at 11 and 2.44 MoM at 13 completed weeks). At 75% detection, maternal age in combination with ITA and PAPP-A measurements have an 8.0% false-positive rate, slightly lower than the 8.8% found for the free β and PAPP-A combination; adding NT measurements reduces false positives for the 2 combinations to 2.0% and 1.8%, respectively.

Conclusion: Serum ITA appears to be a useful first-trimester Down syndrome marker that could replace free β measurements while maintaining performance.

Integrated serum screening for Down syndrome in primary obstetric practice

OBJECTIVES

Integrated serum screening for Down syndrome is potentially more effective than current second-trimester screening. We report results of an intervention trial of integrated serum screening that involved 229 primary prenatal care practitioners throughout Maine.

METHODS

Women provided a first-trimester serum (for PAPP-A) followed by a second-trimester serum (for AFP, uE3, hCG, and DIA). These five marker measurements were used to calculate a Down syndrome risk in the second trimester. Screen-positive women (risk > or = 1:100) were managed according to standard practice.

RESULTS

During 24 months' enrollment, 11 159 women provided a first-trimester sample (61% of women receiving screening services). Nine thousand seven hundred twenty-three women also provided a second-trimester sample; 8773 women satisfied gestational age criteria for testing in both trimesters. Integrated serum screening detected 14 of 16 Down syndrome cases (87%) and 79% after adjustment for trimester-of-ascertainment bias. The initial false-positive rate was 3.2% and was 2.7% when restricted to ultrasound-dated pregnancies. Performance was better than any combination of second-trimester markers. Implementation challenges included initial samples being collected too early and sample matching.

CONCLUSIONS

Integrated serum screening for Down syndrome was successfully implemented in primary care settings; screening performance was consistent with predictions. It provides an accessible and acceptable alternative to screening protocols that require nuchal translucency measurements.

Reference distributions for alpha2-macroglobulin: a comparison of a large cohort to the world's literature

The lack of satisfactory methods for quantifying serum levels and a credible reference material has limited bedside use of serum alpha(2)-macroglobulin (alpha2M) measurements. Great strides have been made in the last few years. The remaining barrier to more relevant and cost effective use of serum protein data for diagnosis and prognosis is the availability of reliable reference intervals from birth to old age for both males and females. A total of 40 publications reporting reference intervals have been identified that meet the criteria used in our prior five studies, and these have been analyzed statistically. On average, previous small studies of these individual proteins agree with our life-long reference ranges over their constrained age ranges. This meta-analysis provides support for our reference ranges and places them in the perspective of previous publications.

Maternal Serum Invasive Trophoblast Antigen (Hyperglycosylated hCG) as a Screening Marker for Down Syndrome during the Second Trimester

Background: Approximately two million pregnancies in the United States are screened for Down syndrome annually by use of second-trimester maternal serum markers. At present, a combination of four markers can identify 75% of affected pregnancies when 5% of screened women are classified as candidates for amniocentesis. Although not currently included in screening panels, invasive trophoblast antigen (ITA) is a promising screening marker in serum or urine in both the second and first trimesters. This study aims at better defining the screening performance of serum ITA in the second trimester.

Methods: In an earlier study, serum samples from an unbiased sampling of 45 Down syndrome (cases) and 238 unaffected (control) pregnancies between 14 and 20 weeks of gestation were collected from various centers in the United States. Samples were aliquoted and stored at −20 °C for 8 years. We measured ITA in these samples and determined the screening performance both univariately and in combination with other screening markers.

Results: The median ITA in Down syndrome pregnancies was &gt;3.00 multiples of the median, higher than that found for human chorionic gonadotropin (hCG) or free β-hCG. At a 5% false-positive rate, ITA univariately detected 38% and 40% of Down syndrome pregnancies, respectively, when assigned by date of last menstrual period or ultrasound date. Modeling yielded rates of 45% and 48%. ITA correlated strongly with hCG and free β-hCG. When substituted for either of these in a multiple marker panel, ITA performed comparably.

Conclusions: This study indicates that serum ITA is an effective marker for Down syndrome. It is highly correlated with both hCG and free β-hCG and could replace either of them in a multiple marker panel.

Reference distributions for complement proteins C3 and C4: a comparison of a large cohort to the world's literature

The lack of credible reference materials and satisfactory methods for quantifying serum levels has limited the bedside use of complement protein (C3 and C4) measurements. However, great technological strides have been made in the last few years. The remaining barrier to a more relevant and cost-effective use of serum protein data for diagnosis and prognosis is the availability of reliable reference intervals from birth to old age for both males and females. Fifty-one publications reporting reference intervals were identified that meet the criteria used in our prior four studies, and these were analyzed statistically. Previous small studies with constrained age ranges agree, on average, with our larger series of life-long reference ranges. This meta-analysis provides support for our reference ranges and places them in the context of previous publications.

Reference distributions for complement proteins C3 and C4: a practical, simple and clinically relevant approach in a large cohort

The two serum proteins of the complement cascade in the highest concentrations, C3 and C4, respond to various conditions in much the same manner as do other positive acute-phase proteins. A major difference is that they are relatively sluggish in response to cytokine drive, requiring several days rather than hours to be detectably elevated by serial measurements. As with other acute-phase proteins, there are many processes that up- or down-regulate synthesis, including infection or inflammation, hepatic failure, and immune-complex formation. Clinicians may find it difficult to distinguish among these processes, because they often occur simultaneously. The situation is further complicated by genetic polymorphism, with rare instances of markedly reduced synthesis and circulating levels, and consequent vulnerability to infection. C3 and C4 are measured for clinical purposes to help define certain rheumatic and immunologically mediated renal diseases. Interpreting the measured blood levels of these two components requires one to consider the intensity of the inflammatory drive, the timing of the suspected clinical process, the production of complement-consuming immune complexes, and the possible existence of benign circumstances. In this fifth article in a series, reference ranges for serum levels of two complement proteins (C3 and C4) are examined. The study is based on a cohort of over 55,000 Caucasian individuals from northern New England, who were tested in our laboratory in 1994-1999. Measurements were standardized against certified reference material (CRM) 470/reference preparation for proteins in human serum (RPPHS), and analyzed using a previously described statistical approach. Individuals with unequivocal laboratory evidence of inflammation (C-reactive protein of 10 mg/L or higher) were excluded. Our results show that the levels of C3 and C4 change little during life and between the sexes, except that they increase slightly and then fall after age 20 in males and at about age 45 in females. When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution well over a broad range. When patient data are normalized in this manner, the distribution parameters can be used to assign a centile corresponding to an individual's measurement, thus simplifying interpretation.

Reference distributions for alpha2-macroglobulin: a practical, simple and clinically relevant approach in a large cohort

In this 11th article in a series, reference values of serum levels alpha(2)-macroglobulin alpha(2)M) are examined. The study is based on a cohort of 40,420 Caucasian individuals from northern New England that were tested in our laboratory between 1994 and 2000. Measurements were standardized against Certified Reference Material (CRM 470)/Reference Preparation for Proteins in Human Serum (RPPHS) and the results analyzed using a previously described statistical approach. Individuals with unequivocal laboratory evidence of inflammation (C-reactive protein >10 mg/L) were excluded in one leg of the study and included in the other, confirming that alpha(2)M does not respond to acute phase drive in man. Nephrotic syndrome, diabetes mellitus, and chronic liver disease have significant effect on levels of alpha(2)M. Dramatic changes occur during life with males higher from birth to age 12, females thereafter have higher values until the ninth decade. When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution well over a broad range. When patient data are normalized in this manner, the distribution parameters can be used to assign a centile corresponding to an individual's measurement thus simplifying interpretation.

Maternal serum-integrated screening for trisomy 18 using both first- and second-trimester markers

OBJECTIVES

To estimate the prenatal screening performance of an integrated serum test for detecting trisomy 18, which combines measurements of first- and second-trimester markers with maternal age to assign patient-specific risks.

METHODS

Published and new observations of maternal serum marker levels in trisomy 18 and unaffected pregnancies are used to derive population parameters. These parameters are then combined in a multivariate Gaussian model to assign patient-specific risks for trisomy 18.

RESULTS

The best combination of serum markers includes pregnancy-associated plasma protein-A in the first trimester and alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin in the second trimester. At a second-trimester risk cutoff of 1 : 100, these 4 markers, in combination with maternal age, detect 90% of trisomy 18 pregnancies at a false-positive rate of 0.1%. The odds of a trisomy 18 pregnancy among screen-positive women are 1 : 4. Without the first-trimester marker, detection is reduced to 67% at about the same false-positive rate.

CONCLUSION

The algorithm described here is highly efficient for detecting trisomy 18 and should be considered by programs that offer serum-integrated screening for Down syndrome.

Evaluation of cell-free fetal DNA as a second-trimester maternal serum marker of Down syndrome pregnancy

BACKGROUND

Second-trimester cell-free fetal DNA (studied only in pregnancies with male fetuses) is higher in maternal serum samples from women carrying Down syndrome fetuses than in unaffected pregnancies. In this study we evaluated the potential performance of fetal DNA as a screening marker for Down syndrome.

METHODS

Data on maternal serum fetal DNA concentrations and the corresponding concentrations of the quadruple serum markers were available from 15 Down syndrome cases, each matched for gestational age and length of freezer storage, with 5 control samples. Analyte values were expressed as multiple(s) of the control or population median. Screening performance of fetal DNA, both alone and when added to estimates of quadruple marker performance, was determined after modeling using univariate and multivariate gaussian distribution analysis.

RESULTS

The median fetal DNA concentration in Down syndrome cases was 1.7 times higher than in controls. In univariate analysis, fetal DNA gave a 21% detection rate at a 5% false-positive rate. When added to quadruple marker screening, fetal DNA increased the estimated detection rate from 81% to 86% at a 5% false-positive rate.

CONCLUSIONS

Cell-free fetal DNA, measured in maternal serum, can modestly increase screening performance above what is currently available in the second trimester. If and when maternal serum fetal DNA can be measured in pregnancies with both male and female fetuses, the utility and cost-effectiveness of adding it as a Down syndrome screening marker should be assessed.

Reference distributions for serum iron and transferrin saturation: a comparison of a large cohort to the world's literature

The appropriate clinical use of serum iron and transferrin saturation (TSAT) requires satisfactory reference intervals from birth to old age, and for males and females. This study identified 54 publications from 1974 to 2001 that met the criteria used in three prior meta-analyses, and these were analyzed statistically. A summary of our review is presented along with our reference population data on these measurements. This analysis places previous publications in perspective and suggests possible reasons for the observed differences. Previous studies of the individual analytes, serum iron, transferrin, and TSAT values agree with the reference ranges presented in this study, although the entire experience over time and between sexes has not been available before. Our 95% reference ranges are somewhat broader than those of the smaller studies, but they agree well with those of the larger ones.

Long QT syndrome in children: the value of rate corrected QT interval and DNA analysis as screening tests in the general population

OBJECTIVE

To evaluate two hypothetical screening strategies for identifying children with long QT syndrome (LQTS), a cause of sudden death in childhood.

METHODS

Families with KVLQT1, HERG, or SCN5A genotypes provided electrocardiographic (ECG) data for this analysis. This is the first time such genotype-phenotype information has been available. Using the LQTS genotype, the distributions of QTc in affected and unaffected children were established and screening performance for various QTc cut off points were modelled. The detection rate for DNA mutation analysis was determined from published experience.

RESULTS

The mean QTc (SD) was 0.484 seconds (0.031) in 117 affected children and 0.420 seconds (0.021) in 133 unaffected children. A QTc cut off of 0.50 seconds in a population of 1 million children would identify 61 of the 200 affected children, and 100 unaffected children. Estimates of testing costs for a screening programme in the newborn period would be $327 869/case detected and $2 222 000/death avoided. Although not presently available for routine use, DNA analysis could, theoretically, identify 100 of the 200 children with LQTS within the same population, along with an estimated 100 unaffected children.

CONCLUSION

The only available screening test for LQTS is ECG measurement. If DNA technology becomes available for screening, unit costs must be very low to be competitive. There are multiple problems with screening for LQTS: only a minority of children will be detected, cost/death avoided is high, and pilot studies would need to be in place for 5-10 years to document efficacy.

Long QT syndrome in children: the value of the rate corrected QT interval in children who present with fainting

OBJECTIVE

A strategy was evaluated for identifying a proportion of children with long QT syndrome (LQTS) using the rate corrected QT interval (QTc) to systematically evaluate children who faint.

METHODS

QTc measurements and rates of fainting for the present analysis are available from families with KVLQT1, HERG, or SCN5A genotypes. QTc distributions in affected and unaffected children were documented and detection and false positive rates were modelled.

RESULTS

The mean QTc (SD) in 117 affected children was 0.484 seconds (0.031), and 0.420 seconds (0.021) among 133 unaffected children. At a cut off of 0.49 seconds, QTc measurement will identify 42.5% of affected and 0.1% of unaffected persons with a history of fainting who are alive at the time of testing. Assumptions include a prevalence of 1:5000 for LQTS, 2% mortality with the first arrhythmia, and a rate of fainting of 50% in affected children and 7% in unaffected children. Given these variables, a QTc cut off of 0.49 seconds detects 42 of 200 affected, along with 70 unaffected children out of a population of 1 million. If QTc > or = 0.49 seconds is found in either parent of children with a QTc of 0.44 through 0.48 seconds, another 21 affected and 25 unaffected children will be identified.

CONCLUSION

Systematically performing QTc measurements as part of the evaluation of children who faint might optimally identify about one third of patients with LQTS with few false positives and thereby offer an opportunity to prevent some sudden deaths.

Reference distributions for serum iron and transferrin saturation: a practical, simple, and clinically relevant approach in a large cohort

The principal considerations driving iron status evaluation are clinical concern for anemia and the possibility of iron-storage disease. Most often, the circulating levels of transferrin (or total iron binding capacity) and serum iron are measured and the percentage of transferrin saturation (TSAT) is then computed. Optimally, reference ranges for these analytes should exclude the effects of the acute phase response, nutritional status, estrogen effect, specific genetic disorders, liver disease, and blood transfusion. The current study reports reference ranges for serum iron and TSAT within a cohort of over 55,000 Caucasians from northern New England, tested in our laboratory between 1994 and 1999. Measurements were standardized against serum reference material (SRM) 937 (for iron) and certified reference material (CRM) 470 (also called reference preparation for proteins in human serum (RPPHS)) (for transferrin), and analyzed using a previously published approach. Individual cases with evidence of inflammation (C-reactive protein > or =10 mg/L), or iron overload (TSAT >80% for males and >70% for females) or serum iron values <5 micro mol/L, were removed. Among the referent individuals, iron and TSAT levels rose slightly until the teen years, at which time levels in males increased while those in females remained essentially constant. Between 20 and 70 years of age, males had 10-15% higher iron levels and 15-20% higher TSAT levels than females. When values were expressed as multiples of the age- and gender-specific median levels, the serum iron and TSAT observations fit log-Gaussian distributions reasonably well from the 20th to 99th centile, and the 10th to the 99th centile, respectively. After normalization, the Gaussian parameters can be used to assign a corresponding centile to an individual's measurement, simplifying interpretation. These data provide new and more detailed reference ranges for serum iron and TSAT.

Using multiples of the median to normalize serum protein measurements

Quantification of serum proteins is useful in the diagnosis and clinical management of many disorders. With the introduction of automated analyzers and standardized reference materials, one of the last barriers to more widespread utilization of these measurements is the lack of availability of reliable and transferable age- and gender-specific reference ranges. One normalization method that deserves consideration is converting values to multiples of the median (MoM) for age and gender. When two analytic methods agree, or differ only by a proportional amount, conversion to MoM can be used to simplify the clinical interpretation of serum protein results. As a test of this method, assay results for IgG, transferrin, and albumin from three Swedish hospitals were normalized using published reference ranges from the United States. All assays were standardized to CRM 470. IgG results were in agreement in mass units, and transferrin measurements were proportionally different. However, there were important, non-proportional differences in albumin measurements. After converting IgG and transferrin measurements to MoM, published reference ranges were appropriate for the Swedish Hospitals.

Reference distributions for the positive acute phase proteins, alpha1-acid glycoprotein (orosomucoid), alpha1-antitrypsin, and haptoglobin: a comparison of a large cohort to the world's literature

Limiting bedside use of positive acute phase protein measurements (alpha1-acid glycoprotein (orosomucoid), alpha1-antitrypsin, and haptoglobin) has been the lack of satisfactory methods for quantifying serum levels and a credible reference material. Great strides have been made in the last few years. The remaining barrier to more relevant and cost-effective use of serum protein data for diagnosis and prognosis is the availability of reliable reference intervals from birth to old age for both males and females. Sixty publications reporting reference intervals have been identified which meet the criteria used in our prior two studies, and these have been analyzed statistically. Previous small studies of these individual proteins agree on average, over their constrained age ranges, with our life-long reference ranges. This meta-analysis provides support for our reference ranges and places them in the perspective of previous publications.

Second-trimester levels of maternal serum human chorionic gonadotropin and inhibin a as predictors of preeclampsia in the third trimester of pregnancy

OBJECTIVE

To determine whether second-trimester maternal serum levels of inhibin A, human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and alpha-fetoprotein (AFP) are predictive of the later onset of preeclampsia in pregnancy.

METHODS

Retrospective evaluation of serum analyte levels in 60 women with preeclampsia compared with 300 controls. Levels of each analyte were compared in women with preeclampsia and controls using matched rank analysis. Analytes that were significantly different between groups were examined with univariate and bivariate Gaussian distribution analysis.

RESULTS

Second-trimester inhibin A (1.36 multiples of the median [MoM]) and hCG (1.40 MoM) levels were significantly but modestly elevated in women who later developed preeclampsia. A combination test of maternal age plus inhibin A and hCG predicted 23% of cases of preeclampsia with 95% specificity. There was a statistically significant trend for inhibin A, but not hCG, levels to be higher when the onset of preeclampsia occurred within a shorter (<17 weeks) interval after collection of the second-trimester screening sample.

CONCLUSIONS

Second-trimester serum levels of inhibin A and hCG are modest predictors of the later onset of preeclampsia. Inhibin A may be a better predictor of early-onset preeclampsia, which is associated with a higher maternal and perinatal morbidity and mortality, than preeclampsia at or near term.

Reference distributions for the positive acute phase serum proteins, alpha1-acid glycoprotein (orosomucoid), alpha1-antitrypsin, and haptoglobin: a practical, simple, and clinically relevant approach in a large cohort

Most clinical conditions are accompanied by corresponding changes in serum levels of some, if not all, of the acute phase proteins. While conditions that affect the acute phase proteins are usually inflammatory in nature, non-inflammatory conditions also can cause changes (e.g., malnutrition, some malignancies without secondary inflammation, and genetic polymorphism). Only after the confounding effects of non-inflammatory conditions are taken into account can these measurements be used to detect and stage the inflammatory process and to evaluate the impact of treatment. In this third article in a series, reference ranges for serum levels for three of the acute phase proteins that increase during inflammation are examined: alpha1-acid glycoprotein (orosomucoid), alpha-antitrypsin, and haptoglobin. The study is based on a cohort of 55,199 Caucasian individuals from northern New England, tested in our laboratory between 1994 and 1999. Measurements were standardized against CRM 470 (RPPHS) and analyzed using a previously described statistical approach. Individuals with unequivocal laboratory evidence of inflammation (C-reactive protein of 10 mg/l or higher) were excluded. Levels of a,-acid glycoprotein changed little during life and between the sexes. Levels of alpha1-antitrypsin varied somewhat by age, rising slightly beyond age 55; males followed a pattern similar to that for females. For this protein, it was necessary to apply two equations to describe the lower levels associated with certain phenotypes. Haptoglobin levels fell significantly during the first decade of life for both males and females and climbed thereafter. Males and females displayed a similar pattern. When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution well over a broad range. When patient data are normalized in this manner, the distribution parameters can be used to assign a centile corresponding to an individual's measurement, thus simplifying interpretation.

Relationship between lipoprotein- and oxidation-related variables and atheroma lipid composition in subjects undergoing coronary artery bypass graft surgery

The relationship between atheroma lipid composition and serum lipoprotein and oxidation measurements has not been fully explored. To address this question, we studied serum, plasma, and aortic wall specimens from 66 subjects undergoing coronary artery bypass graft surgery. The lipid composition of aortic specimens was characterized in terms of cholesterol ester and cholesterol crystal plus phospholipid by using hot-stage polarizing light microscopy; tissue oxidation status was assessed by measuring conjugated dienes. Serum lipoprotein-related measurements included total cholesterol, triglyceride, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, apolipoproteins B and AI, and lipoprotein(a). Oxidation status was assessed by measuring LDL mobility, thiobarbituric acid-reactive substances, LDL conjugated dienes, and IgG and IgM autoantibodies against oxidized LDL. Fasting blood glucose was also determined. Lesion cholesterol crystal plus phospholipid content was associated inversely with serum HDL cholesterol levels (r=-0.279, P=0.029) and positively with fasting blood glucose (r=0.359, P=0.016), LDL mobility (0.276, P<0.05), and IgM autoantibodies against oxidized LDL (r=0.272, P=0.037). There was also a significant relationship between the level of aortic tissue conjugated dienes and plasma LDL mobility (r=0.332, P=0.007). In multivariate analysis, IgM autoantibodies against oxidized LDL, fasting blood glucose, and LDL mobility, in descending order of significance, together accounted for 35% of the variability in aortic lesion cholesterol crystal plus phospholipid content. These data support direct and independent roles for oxidation and hyperglycemia in the pathophysiology of atherosclerosis.

Reference distributions for the negative acute-phase proteins, albumin, transferrin, and transthyretin: a comparison of a large cohort to the world's literature

Clinical interpretation of the acute-phase proteins--albumin, transferrin, and transthyretin--has been hampered by the lack of accurate and precise methods for quantifying the levels and a stable and respected reference material. Now that these issues have been addressed, the community is faced with the need for credible age- and gender-specific reference values. The number of publications that address this issue, even for an analyte as familiar as albumin, is small and, in most cases, such publications lack the relevant data that would allow a combined experience to be created. We have identified 40 studies that meet our criteria: a description of the study participants' health status, of the statistical methodology, and of the laboratory technique and/or reference material used. Few of these studies reported values stratified by gender. A summary of the published median levels by age is presented for the three analytes, along with our own age- and gender-specific medians based on a large cohort. Ten of the studies presented a 95 percent reference range, in close agreement with ours where selection was based upon reported diagnosis rather than upon determination of individual health status. This meta-analysis provides support for the reliability of our recently published methodology and reference data for the clinical interpretation of individual albumin, transferrin, and transthyretin values. As with most laboratory measurements, clinical interpretation requires that other laboratory and clinical factors be considered.

Reference distributions for the negative acute-phase serum proteins, albumin, transferrin and transthyretin: a practical, simple and clinically relevant approach in a large cohort

Inflammation is associated with diverse clinical conditions accompanied by characteristic changes in serum levels of the acute-phase proteins that can be used to stage the inflammatory process and evaluate the impact of treatment. Some acute-phase proteins increase during inflammation, while others, such as albumin, transferrin, and transthyretin, decrease. The current study reports reference ranges for serum levels of albumin, transferrin, and transthyretin based on a cohort of over 124,000 Caucasian individuals from northern New England, tested in our laboratory between 1986 and 1998. Measurements were standardized against CRM 470 (RPPHS) and analyzed using a previously validated statistical approach. Individuals with laboratory evidence of inflammation (C-reactive protein of 10 mg/L or higher) were excluded. The levels of all three analytes varied by age, generally rising until the second or third decade of life and then decreasing thereafter. Albumin and transthyretin levels were higher during midlife among males as compared to females; the maximum being at 25 years for albumin (5%) and 35 years for transthyretin (16%). In contrast, above the age of 10 years, transferrin levels were increasingly higher among females (7% at 20 years). When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution. When patient data are normalized in this manner, the distribution parameters can be used to assign a corresponding centile to an individual's measurement simplifying interpretation. The ultimate interpretation of an individual's measurement relies upon the clinical setting.

Lipoprotein(a) as a risk factor for ischemic heart disease: metaanalysis of prospective studies

Although in vitro studies support a pathophysiologic role for lipoprotein(a) [Lp(a)] in the development of atherosclerosis, and retrospective studies consistently report that there is a relationship between Lp(a) and ischemic heart disease (IHD), the conclusions drawn from prospective studies about this relationship have been inconsistent. To address this issue, we have performed a metaanalysis of data available from prospective studies. Lp(a) concentrations expressed as mass units vary markedly between studies, reflecting the need for assay standardization. In 12 of 14 prospective studies, Lp(a) concentrations are higher in subjects who later develop IHD (cases) than in those who do not (controls), although there is variation in the size of the effect. Sample storage temperature may contribute to this variability. When the studies are analyzed collectively, Lp(a) concentrations are significantly higher in cases than in controls, and the extent of the effect is similar in men and women. These findings provide evidence in support of a causal role for Lp(a) in the development of atherosclerosis. Measurement of Lp(a) may be useful to guide management of individuals with a family history of IHD or with existing disease. The separation in values between cases and controls is not, however, sufficient to allow the use of Lp(a) as a screening test in the general population.

Lipoprotein(a) as a risk factor for ischemic heart disease: metaanalysis of prospective studies

Although in vitro studies support a pathophysiologic role for lipoprotein(a) [Lp(a)] in the development of atherosclerosis, and retrospective studies consistently report that there is a relationship between Lp(a) and ischemic heart disease (IHD), the conclusions drawn from prospective studies about this relationship have been inconsistent. To address this issue, we have performed a metaanalysis of data available from prospective studies. Lp(a) concentrations expressed as mass units vary markedly between studies, reflecting the need for assay standardization. In 12 of 14 prospective studies, Lp(a) concentrations are higher in subjects who later develop IHD (cases) than in those who do not (controls), although there is variation in the size of the effect. Sample storage temperature may contribute to this variability. When the studies are analyzed collectively, Lp(a) concentrations are significantly higher in cases than in controls, and the extent of the effect is similar in men and women. These findings provide evidence in support of a causal role for Lp(a) in the development of atherosclerosis. Measurement of Lp(a) may be useful to guide management of individuals with a family history of IHD or with existing disease. The separation in values between cases and controls is not, however, sufficient to allow the use of Lp(a) as a screening test in the general population.

Second trimester screening for Down's syndrome using maternal serum dimeric inhibin A

OBJECTIVES

To determine the second trimester Down's syndrome screening performance of maternal serum dimeric inhibin A, both alone and in combination with existing serum markers.

SETTING

A case-control set of serum samples from patients with Down's syndrome (52) and subjects with matched unaffected pregnancies obtained in a previous cohort study before second trimester amniocentesis and karyotyping. The amniocenteses were performed for reasons other than a positive serum screening test result.

METHODS

For each serum from a Down's syndrome pregnancy, five serum samples from pregnancies with a normal karyotype were matched for recruitment centre, gestational age, maternal age, and date of amniocentesis. A specific form of inhibin (dimeric inhibin A) was measured using monoclonal antibodies. Measurements of alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin and its free beta subunit were already available. Screening performance was modelled using distribution variables of the analytes coupled with the 1993 age distribution of pregnant women in the United States.

RESULTS

The median dimeric inhibin A level was 2.10 times higher in Down's syndrome pregnancies. When dimeric inhibin A was combined with maternal age and three other serum markers (alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin) the Down's syndrome detection rate increased to 75% (from 66%) at a 5% false positive rate. If dimeric inhibin A could be added for less than $31 (ranging from $16 to $39 depending on the detection rate, markers chosen, and method of dating), the cost of detecting each Down's syndrome pregnancy and the number of procedure related fetal losses would both be reduced.

CONCLUSIONS

The addition of dimeric inhibin A to prenatal screening programmes for Down's syndrome should be considered, or possibly it could be substituted for an existing serum marker. One barrier to implementation in the United States, however, is the unavailability of kits with Food and Drug Administration approval.

The relationship between apolipoprotein E and serum oxidation-related variables is apolipoprotein E phenotype dependent

To examine the relationship between apolipoprotein E and serum oxidation status, we assayed apolipoprotein E level, apolipoprotein E phenotype, and levels of lipid peroxides and transition metal ions and their binding proteins in sera from apparently healthy individuals. The study group included 129 women aged 22-63 years and 53 men aged 22-56 years. Among subjects with apolipoprotein E 4/3 phenotype, lipid peroxide levels were higher compared with E 3/2 phenotype (786 +/- 182 nmol/l vs. 659 +/- 174 nmol/l, P = 0.015), and ceruloplasmin levels were slightly higher compared with apolipoprotein E 3/3 phenotype (0.28 +/- 0.08 mg/l vs. 0.26 +/- 0.06 mg/l, P = 0.035). In the study group as a whole, there were significant associations between serum apolipoprotein E level, and serum levels of ceruloplasmin (r = 0.266, P < 0.001) and ferritin (r = 0.2, P < 0.007). Among subjects with apolipoprotein E 4/3 phenotype, there was a significant association between serum apolipoprotein E and lipid peroxide levels (r = 0.470, P < 0.01), which was not apparent among subjects with E 3/3 or E 3/2 phenotypes. In multivariate analysis, apolipoprotein E phenotype was a small but significant independent contributor to variation in serum lipid peroxide levels. These data suggest that there may be heterogeneity among apolipoprotein E phenotypes in their relationships with serum lipid oxidation status.

hCG and the free beta-subunit as screening tests for Down syndrome

Published studies have reached varying conclusions as to the benefit of replacing human chorionic gonadotropin (hCG) measurements with the free beta-subunit of hCG (the free beta-subunit) for Down syndrome screening. One study reports 14 per cent higher detection for the free beta-subunit, while another finds an actual loss in detection. To explore this issue further, we directly compared the screening performance of hCG and the free beta-subunit, alone and in combination with other serum markers, using banked sera obtained prior to amniocentesis and karyotyping. Altogether, 52 Down syndrome and 5065 unaffected pregnancies were studied. Sera were thawed and assayed for hCG and the free beta-subunit over 1 year. At a 5 per cent false-positive rate, the detection rate for hCG in combination with maternal age and alpha-fetoprotein was higher than when the free beta-subunit was substituted (62 versus 57 per cent). Ultrasound dating and adding unconjugated oestriol both increased detection. The present findings, along with those from six case control studies (our re-analysis), indicate that the screening performances of hCG and the free beta-subunit are similar (median change in detection 0, range -8 to +3 per cent). Under optimal sample collection and transportation conditions, laboratories can expect to achieve similar screening performance using either hCG or the free beta-subunit measurements.