Hypersecretion of the alpha-subunit in clinically non-functioning pituitary adenomas: Diagnostic accuracy is improved by adding alpha-subunit/gonadotropin ratio to levels of alpha-subunit

BACKGROUND

In vitro, the majority of clinically non-functioning pituitary adenomas (NFPAs) produce gonadotropins or their alpha-subunit; however, in vivo, measurements of alpha-subunit levels may not accurately detect the hypersecretion of the alpha-subunit.

AIM

We wanted to estimate the reference intervals and decision limits for gonadotropin alpha-subunit, LH and FSH levels, and aratio (alpha-subunit/LH+FSH), especially taking into consideration patient gender and menstrual status. Furthermore, we wanted to examine if the diagnostic utility of alpha-subunit hypersecretion was improved when the alpha-ratios, rather than simply the alpha-subunit levels, were measured in patients with NFPAs.

MATERIAL AND METHODS

Reference intervals for gonadotropin alpha-subunit serum levels and alpha-ratios were established in 231 healthy adults. The estimated cut-off limits were applied to 37 patients with NFPAs. Gonadotropin alpha-subunit, LH and FSH levels were measured and alpha-ratios were calculated.

RESULTS

In healthy adults, the cut-offs for alpha-subunit levels were significantly different between men and pre- and postmenopausal women: the cut-offs were 1.10, 0.48 and 3.76 IU/l, respectively. Using these estimated cut-offs, increased alpha-subunit levels were identified in 10 out of 37 (27%) patients with NFPAs. By adding alpha-ratio, in combination with alpha-subunit levels, 23 patients out of 37 (62%) were identified as having elevated alpha-subunit hypersecretion, and 22 out of these 23 patients (96%) had increased alpha-ratios. One premenopausal patient out of 23 had elevated alpha-subunit level but a normal alpha-ratio.

CONCLUSION

Our data suggest that adding the simple calculation of alpha-ratio improves the ability of detecting gonadotropin alpha-subunit hypersecretion and thereby indentifying patients with NFPAs.

Biological variation of thyroid autoantibodies and thyroglobulin

BACKGROUND

It has been shown that the level of serum thyroid antibodies affects serum thyrotropin (TSH) concentrations in men and women, and that these autoantibodies in combination with serum TSH are predictive of future thyroid disease. As the biological variation of these autoantibodies is unknown, we investigated this in fertile women during one complete regular menstrual cycle.

METHODS

A total of 24 healthy women (23-46 years) were investigated twice a week between 07:30 and 11:00 h. Antibodies against thyroid peroxidase (TPOAb), thyroglobulin (TgAb), and thyrotropin receptor (TRAb) were measured in serum, as well as thyroglobulin (Tg). TPOAb, TgAb and Tg were determined on an AutoDELFIA system (Perkin Elmer/Wallac) and TRAb by a radioreceptor assay from Brahms Diagnostica.

RESULTS

All 24 women had measurable levels of TPOAb and TgAb in all samples, and nine women had antibodies above the upper reference limit of the laboratory (6 had TPOAb >10 kIU/L, 6 had TgAb >20 kIU/L and 1 had TRAb >0.75 IU/L). Eight women had Tg below the lower reference limit, five of whom had elevated TgAb. Variations in the thyroid antibodies were random and not related to the menstrual cycle. For TPOAb (2.5-258 kIU/L), the CV biological was 11.3%, while the CV analytical was 10.6%. For TgAb (5.6 to 148 kIU/L) CV biological was 8.5% and CV analytical was 9.0%. The woman with TRAb had a CV biological of 4.8%, while the analytical variation in duplicates was 3.9% at a level of 2.8 IU/L.

CONCLUSIONS

It is possible to measure TPOAb and TgAb in all samples with the AutoDELFIA. There is no systematic variation in autoantibodies during the menstrual cycle. The biological coefficient of variation for TPOAb and TgAb was 11.3% and 8.5%, respectively.

Minimally processed fresh frozen human reference sera: preparation, testing, and application to international external quality assurance

The preparation of unmodified or minimally processed fresh frozen human sera is described, as well as the previous use of such sera, e.g. in Nordic and international external quality assurance (EQA) activities. The unmodified serum is prepared from fresh donors' blood collected in dry bags and allowed to coagulate. The serum is collected "on the clot", pooled, filtered, mixed, dispensed in polypropylene vials and frozen at -80 degrees C without further processing. Some batches were slightly modified by spiking or dilution. Critical steps of the production and use of the sera are described and improvements are discussed. A total of 34 different batches have been prepared since 1985. Results from homogeneity and stability studies are presented. The studies cover 18 routine components in serum stored at +4 degrees C to 37 degrees C for up to 34 days. Good stability was observed for storage of all components, with the exception of triglyceride. Amylase, creatininium, glucose, gamma-glutamyltransferase, urate (and perhaps carbamide) showed deterioration after 13 days of incubation at 37 degrees C. The long-term stability at -80 degrees C is reviewed and new data are presented, e.g. as consensus values from EQA schemes, where the same serum has been sent out three times over 5 years, and from reference measurement procedure values that have been assigned twice with an interval of 5 years. Furthermore, a 10-year stability study has been started.

Expression of Leptin Receptor Isoforms and Effects of Leptin on the Proliferation and Hormonal Secretion in Human Pituitary Adenomas

OBJECTIVE

To pursue whether leptin regulates anterior pituitary cells, we studied the ex vivo expression of several isoforms of the leptin receptor (OB-R) as well as the in vitro effects of leptin administration in human pituitary adenomas.

METHODS

OB-R mRNA expression and in vitro response to leptin were studied in 39 pituitary macroadenomas.

RESULTS

All 4 OB-R subtypes were expressed in most adenomas. The expression was significantly more pronounced in GH-secreting adenomas as compared to non-functioning tumor cells (p < 0.05). Leptin administration in vitro did not significantly influence cell proliferation or the secretion of GH, FSH, LH or alpha-subunit.

CONCLUSIONS

(1) Several isoforms of the OB-R, including the signal transducing full-length receptor, are expressed in most human pituitary adenomas. (2) This expression ex vivo is not associated with significant effects of leptin in vitro.

Establishment of a serum thyroid stimulating hormone (TSH) reference interval in healthy adults. The importance of environmental factors, including thyroid antibodies

It has previously been shown that thyroid antibodies affect thyroid stimulating hormone (TSH) concentrations in men and women and that TSH levels are predictive of future thyroid disease. We investigated the validity of the National Academy of Clinical Biochemistry (NACB) guidelines regarding the TSH reference interval by studying 1512 individuals. Two hundred and fifty had at least one thyroid antibody, 121 were taking medications other than estrogens and occasional analgesics, and 105 reported a family history of thyroid disease. Serum TSH, thyroid peroxidase antibodies (TPOab) and thyroglobulin antibodies (Tgab) were determined on AutoDELFIA and TSHRab by a radioreceptor assay (RRA) from Brahms Diagnostica. For individuals without thyroid antibodies and other risk factors, no effect of age and gender was seen for serum TSH. Neither medication nor the presence of Tgab alone had any influence on serum TSH. TPOab alone or in combination with Tgab were associated with an increased serum TSH level. The 'cumulative percentage distributions' of subgroups, as well as the combined population, was In-Gaussian distributed. The central 95% of the population was within the 95% CI in rankit-plots. Consequently, a common reference interval for serum TSH of 0.58-4.07 mlU/l for all adults between 17 and 66 years of age was established. This reference interval is much higher than expected from the NACB-guidelines.

Growth hormone receptor expression and function in pituitary adenomas

OBJECTIVE AND DESIGN

Hypopituitarism, in particular GH deficiency, is prevalent in patients with clinically nonfunctioning pituitary adenomas (NFPAs) both before and after surgery. The factors regulating the growth of pituitary adenomas in general and residual tumour tissue in particular are not fully characterized, and the effect of GH and IGF-I on human pituitary cell proliferation has not previously been reported. In NFPA tissue from 14 patients we evaluated GH receptor (GHR) expression and signal transduction, and the effect of GH and IGF-I exposure on cell proliferation and hormone secretion in vitro.

MEASUREMENTS

Tissue samples from 14 NFPAs were investigated. Expression of GHR in tissue samples was assessed by reverse transcription polymerase chain reaction (RT-PCR). Six tumours were immunostained with a GHR antibody. In the cell cultures, STAT5 (signal transducer and activator of transcription 5) phosphorylation was measured by Western blot analysis as an index of GHR signalling; cell proliferation was evaluated by [H3]-thymidine incorporation and glycoprotein hormone production analysed by radioimmunoassay (RIA).

RESULTS

All adenomas investigated expressed the GHR, but there was no detection of STAT5 phosphorylation. Overall, GH and IGF-I administration did not significantly stimulate cell proliferation in vitro, although some individual adenomas exhibited a proliferative response to various extents. GH also did not significantly influence glycoprotein hormone secretion in vitro.

CONCLUSION

GH receptors are expressed in human pituitary adenoma cells but their functional role is uncertain. GH and IGF-I do not consistently influence the proliferation of cultured pituitary adenoma cells.

Graphical interpretation of confidence curves in rankit plots

A well-known transformation from the bell-shaped Gaussian (normal) curve to a straight line in the rankit plot is investigated, and a tool for evaluation of the distribution of reference groups is presented. It is based on the confidence intervals for percentiles of the calculated Gaussian distribution and the percentage of cumulative points exceeding these limits.

The process is to rank the reference values and plot the cumulative frequency points in a rankit plot with a logarithmic (ln=log

This is a conservative validation, which is more demanding than the Kolmogorov-Smirnov test. The graphical presentation, however, makes it easy to disclose deviations from ln-Gaussianity, and to make other interpretations of the distributions, e.g., comparison to non-Gaussian distributions in the same plot, where the cumulative frequency percentage can be read from the ordinate. A long list of examples of ln-Gaussian distributions of subgroups of reference values from healthy individuals is presented. In addition, distributions of values from well-defined diseased individuals may showup as ln-Gaussian.

It is evident from the examples that the rankit transformation and simple graphical evaluation for non-Gaussianity is a useful tool for the description of sub-groups.

Serum lactate dehydrogenase isoenzyme 1 in patients with seminoma stage I followed with surveillance

Serum lactate dehydrogenase isoenzyme I catalytic concentration (S-LD-1) was measured in patients with testicular seminoma clinical stage I followed with surveillance after orchiectomy. The serum samples were obtained before orchiectomy in 110 patients (group A) and soon after orchiectomy in 55 patients (group B). In group A, 60 patients (55%) had elevated S-LD-1 and 10 patients (9%) had elevated serum human chorionic gonadotropin concentrations (S-hCG). In group B, median S-LD-1 was lower than that of group A and decreased with increasing time after orchiectomv (p = 0.001, Jonckheere-Terpstra test, one-sided). After a median follow-up of 5.1 years, 23 patients (21%) in group A had relapses. The patients with elevated S-LD-1 and those with normal S-LD-1 had a similar relapse-free survival (p = 0.79, log-rank test). Thus patients with seminoma stage I had elevated S-LD-1 more often than elevated S-hCG but an elevation in S-LD-1 did not predict a relapse during follow-up with surveillance. Further studies are required to elucidate the value of S-LD-1 in monitoring the surveillance of patients with seminoma stage I.

Magnesium reduces insulin-stimulated glucose uptake and serum lipid concentrations in type 1 diabetes

A magnesium (Mg) deficit has been described in patients with type 1 diabetes, and it has been related to the development of cardiovascular disease. We tested the hypothesis that type 1 diabetic patients have deficits in dietary Mg intake and that proper long-term (24 weeks) oral Mg supplementation would reduce cardiovascular risk factors. Therefore, the Mg status, dietary Mg intake, and the effect of Mg supplementation were evaluated in 10 type 1 diabetic patients and 5 control subjects. Muscle Mg content was decreased by 7% in the type 1 diabetic patients, and it increased by 5% after 24 weeks of oral MgO supplementation. Acute and chronic Mg supplementation decreased serum total cholesterol, serum low-density lipoprotein (LDL)-cholesterol, and apolipoprotein B. Insulin-stimulated glucose uptake decreased by 35% after 24 weeks of oral MgO supplementation. Eight of 10 patients with type 1 diabetes had a daily intake of Mg below 90% of the recommended daily allowance. In conclusion, a Mg deficit was found in type 1 diabetic patients. The deficit might be due partly to a relatively Mg-deficient diet. Mg repletion was associated with a decrease in atherogenic lipid fractions and a reduced insulin-stimulated glucose uptake.

Serum lactate dehydrogenase isoenzyme 1 and relapse in patients with nonseminomatous testicular germ cell tumors clinical stage I

Serum lactate dehydrogenase isoenzyme 1 catalytic concentration (S-LD-1) was measured at the time of orchiectomy in 104 patients with nonseminomatous testicular germ cell tumors (NSTGCT) clinical stage I who participated in a randomized study comparing surveillance after orchiectomy (group I) and radiotherapy (group II). For 68 patients, S-LD-1 was measured in a serum sample before or on the day of the orchiectomy. Twenty-seven patients (40%) had elevated S-LD-1; median 102 U/L (range 41-335). For the remaining 36 patients. S-LD-1 was measured in a serum sample after orchiectomy: 8 of these patients (22%) had elevated S-LD-1. S-LD-1 was normalized shortly after surgery in most patients with a preorchiectomy elevated S-LD-1. Fifteen of the 68 patients relapsed: 9 out of 27 with an elevated S-LD-1 and 6 out of 41 patients with normal S-LD-1 (p = 0.13, Fisher's exact test). In group 1, those with a preoperatively elevated S-LD-1 had a lower 8-years' relapse-free survival than those with a normal S-LD-1 (40% vs. 80%, p = 0.003, log-rank test). The role of S-LD-1 in the staging, prognostication and monitoring of patients with NSGCT clinical stage I should be further explored in a large, prospective study.

Serum lactate dehydrogenase isoenzyme 1 and prediction of death in patients with metastatic testicular germ cell tumors

The International Germ Cell Cancer Collaborative Group study of patients with metastatic testicular germ cell tumors showed that catalytic concentration of serum lactate dehydrogenase (S-LD), serum alpha-fetoprotein concentration (S-AFP), and serum human chorionic gonadotropin concentration (S-hCG) predicted death from tumor. The recent international TNM classification (T primary tumor, N lymph node metastasis, M distant metastasis) is based on these results. The aim of our study was to evaluate whether catalytic concentration of S-LD isoenzyme 1 (S-LD-1) was a better predictor than the criteria used for the international classification. In an evaluation series of 44 patients from Odense University Hospital, Denmark, a raised S-LD-1 (>1.0 x upper limit of reference values) had a predictive value for death from tumor in 5-years observation of 46%. The predictive value was 46% for S-LD, 25% for S-AFP, and 40% for S-hCG. A normal SLD-1 had a predictive value for survival over 5-years observation of 100%. It was 81% for S-LD, 75% for SAFP, and 77% for S-hCG. The fraction of the patients who died of tumor and had a raised tumor marker value was 100% for S-LD-1, 46% for S-LD, 9% for S-AFP, and 18% for S-hCG. The fraction of patients with a normal serum tumor marker value among those who survived was 61% for S-LD-1, 81% for S-LD, 94% for SAFP, and 94% for S-hCG. A validation series of 37 patients treated at the University of Texas MD Anderson Cancer Center showed similar findings. Combining the patients in the two series, a raised value of SLD-1 classified more patients into a subgroup with an impaired survival (53%) than S-LD (35%), S-AFP (6%), or S-hCG (11%), and the high risk subgroups based on the international classification (40%). The findings have implications for the staging and treatment of patients with metastatic testicular germ cell tumors.

Analytical quality specifications for serum lactate dehydrogenase isoenzyme 1 based on clinical goals

The aim of the study was to deduce analytical quality specifications for the determination of catalytic concentration of serum lactate dehydrogenase isoenzyme 1 (S-LD-1) according to clinical goals (the clinical utility model). We defined clinical goals for false positive and false negative S-LD-1 measurements in the monitoring of patients with testicular germ cell tumors (TGCT), clinical stage I, on a surveillance only program. The absolute S-LD-1 catalytic concentrations were routinely corrected for contamination from preanalytical hemolysis. A reference group of 37 men had a near In-Gaussian distribution for the absolute S-LD-1 catalytic concentration. The geometric mean was 76 U/l and an S-LD-1 >128 U/l (99.72 percentile, the decision limit) indicated a high risk of a relapse of TGCT. We have previously shown that an S-LD-1 >160 U/l (treatment limit) was associated with a suboptimal outcome from the treatment of metastatic TGCT. The maximum allowable analytical positive bias was 5 U/l, and the maximum allowable analytical negative bias was -32 U/l. The maximum allowable analytical coefficient of variation, CV(A), was 11% (approximately 14 U/l) at a bias = -5 U/l. For S-LD-1 measurements not corrected for hemolysis, the decision limit was 145 U/l, the maximum allowable negative bias -19 U/l, and CV(A) 8%(approximately 12 U/l). A routine correction for hemolysis had a large impact on the analytical quality specifications.

Effect of moderate improvement in metabolic control on magnesium and lipid concentrations in patients with type 1 diabetes

OBJECTIVE

To evaluate the effect of clinically obtainable improvements in metabolic control in patients with type 1 diabetes on biochemical cardiovascular risk factors.

RESEARCH DESIGN AND METHODS

Blood and 24-h urinary samples were obtained from 49 patients with type 1 diabetes before and after a run-in period and after 3 months of intervention, with frequent adjustment of insulin dosage according to measured blood glucose concentrations.

RESULTS

The intervention caused a mean insulin dosage increment of 10%, a 20% decrease in fasting plasma glucose concentration, a 10% decrease in albumin corrected serum fructosamine, and a somewhat lesser decrease in HbAlc.A 14% decrease in the renal excretion of magnesium (Mg) was observed, but without a change in average serum Mg concentration. Serum HDL cholesterol increased 4%, and serum triglycerides decreased 10% as an average. Looking at individual patients, the decrease in serum triglycerides correlated with both the change in serum total Mg concentration and with the increase in insulin dosage. Using the change in serum total Mg concentration and in insulin dosage as independent variables in a multiple regression analysis, the coefficient of correlation with the decrease in serum triglycerides was 0.52.

CONCLUSIONS

Moderate but clinically obtainable improvement of metabolic control in patients with type 1 diabetes seems to reduce the loss of Mg, increase serum HDL cholesterol, and decrease serum triglycerides. The decrease in serum triglycerides was associated with the change in serum total Mg concentration. These reductions in Mg loss and serum triglycerides might reduce the risk of developing cardiovascular disease in patients with type 1 diabetes.

Evaluation of growth hormone assays using ratio plots

To permit comparison between growth hormone (GH) results obtained using the Pharmacia polyclonal assay and the Delfia monoclonal assay, we used both methods to measure GH concentrations in peak GH responses to the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test and in unstimulated samples from 40 healthy adults and 31 patients with suspected GH deficiency. Ratio plots were used for the comparison, and acceptability criteria were based on inherent analytical imprecision and on analytical quality specifications. The mean ratio (r; Pharmacia/Delfia) for the peak GH responses in 40 healthy adults was calculated to be 1.59, and the 95% prediction interval for ratios fulfilling the imprecision criterion was applied. For GH values >1 mIU/L, the peak and unstimulated GH ratios in healthy adults and patients were within the 95% prediction interval, and fulfilled the biological criterion as well. Therefore, the conversion factor of 1.59 is applicable for the evaluation of GH-stimulation tests.

Evaluation of growth hormone assays using ratio plots

To permit comparison between growth hormone (GH) results obtained using the Pharmacia polyclonal assay and the Delfia monoclonal assay, we used both methods to measure GH concentrations in peak GH responses to the pyridostigmine-growth-hormone-releasing-hormone (PD-GHRH) test and in unstimulated samples from 40 healthy adults and 31 patients with suspected GH deficiency. Ratio plots were used for the comparison, and acceptability criteria were based on inherent analytical imprecision and on analytical quality specifications. The mean ratio (r; Pharmacia/Delfia) for the peak GH responses in 40 healthy adults was calculated to be 1.59, and the 95% prediction interval for ratios fulfilling the imprecision criterion was applied. For GH values &gt;1 mIU/L, the peak and unstimulated GH ratios in healthy adults and patients were within the 95% prediction interval, and fulfilled the biological criterion as well. Therefore, the conversion factor of 1.59 is applicable for the evaluation of GH-stimulation tests.

Graphical interpretation of analytical data from comparison of a field method with a Reference Method by use of difference plots

Various viewpoints have been offered regarding the appropriate use of scatter plots or difference plots (bias plots or residual plots) in comparing analytical methods. In many of these discussions it seems the basic concepts of identity (within inherent imprecision) and acceptability based on analytical goals (analytical quality specifications) have been forgotten. With the increasing number of Reference Methods in laboratory medicine, these basic concepts are becoming more important in validation of field methods. Here we describe a simple and effective graphical test of these hypotheses (identity and acceptability) by use of difference plots. These plots display the underlying hypothesis before the measured differences are plotted and allow interpretation of the results according to specific criteria. We further describe simple but effective interpretations of the data, when the hypothesis is not fulfilled, by using two data sets drawn from comparisons of field methods for S-creatinine with a Reference Method for this analyte. The difference plot is a graphical tool with related simple statistics for comparison of a field method with a Reference Method, focusing on (a) identity within the inherent analytical imprecision or (b) acceptability within analytical quality specifications. Calculation of the standard deviation of the differences is an indispensable tool for evaluation of aberrant-sample bias (matrix effects).

Graphical interpretation of analytical data from comparison of a field method with reference method by use of difference plots

Various viewpoints have been offered regarding the appropriate use of scatter plots or difference plots (bias plots or residual plots) in comparing analytical methods. In many of these discussions it seems the basic concepts of identity (within inherent imprecision) and acceptability based on analytical goals (analytical quality specifications) have been forgotten. With the increasing number of Reference Methods in laboratory medicine, these basic concepts are becoming more important in validation of field methods. Here we describe a simple and effective graphical test of these hypotheses (identity and acceptability) by use of difference plots. These plots display the underlying hypothesis before the measured differences are plotted and allow interpretation of the results according to specific criteria. We further describe simple but effective interpretations of the data, when the hypothesis is not fulfilled, by using two data sets drawn from comparisons of field methods for S-creatinine with a Reference Method for this analyte. The difference plot is a graphical tool with related simple statistics for comparison of a field method with a Reference Method, focusing on (a) identity within the inherent analytical imprecision or (b) acceptability within analytical quality specifications. Calculation of the standard deviation of the differences is an indispensable tool for evaluation of aberrant-sample bias (matrix effects).

The influence of analytical bias on diagnostic misclassifications

Quality specifications for analytical imprecision and bias based on the state of the art; 'biology' and 'analysis of clinical situations' have been proposed by several scientists. Most interesting is the assessment of 'diagnostic misclassifications' based on direct evaluation of the consequences of analytical bias on the percentage of false positives and false negatives from a clinical decision situation, or based on the percentage of healthy individuals outside each reference limit when common reference intervals are used. With use of graphical or computer simulations assuming increasing (positive or negative) analytical bias, the expected percentage of misclassifications can be estimated- and, for the error for which the outcome (the fraction of misclassifications) is considered unacceptable, the maximum allowable analytical bias can be defined. An overview is given of previous proposals for specification of allowable analytical bias, and new examples are presented: (i) for S-transferrin. an analytical bias of +10% will increase the percentage of healthy individuals with measured concentration values above the upper reference limit from 2.5 to 10% (ii) the percentage of healthy men with concentration values for S-cholesterol above 6.2 mmol/l (240 mg/dl) will vary between 25 and 85% for analytical bias from - 1.0 to +1.0 mmol/l (+/- 16%): (iii) for glycated haemoglobin, two examples are given which illustrate the effect of analytical bias on the risk of retinopathy and so-called 'microalbuminuria' for measured values identical to the target 7.5% and 10.1% glycated haemoglobin, respectively. It is concluded that analytical bias may have significant impact on diagnostic performance, better standardization is needed, and quality specifications for allowable analytical bias should be based on medical usefulness criteria or, if such data are not available, on biological criteria.

Consensus of a group of professional societies and diagnostic companies on guidelines for interim reference ranges for 14 proteins in serum based on the standardization against the IFCC/BCR/CAP Reference Material (CRM 470). International Federation of Clinical Chemistry. Community Bureau of Reference of the Commission of the European Communities. College of American Pathologists

The release in 1993 of a new reference material for serum proteins, CRM 470/RPPHS 5 has given rise to a great improvement in the between-laboratory variability of serum protein measurements worldwide. Conversion to the new reference material results in significant changes in reference values for some proteins. The establishment of new reference ranges will take a considerable time, and in the interim several professional societies and diagnostic companies have agreed to use consensus reference ranges based on studies already undertaken.

Robust nonradioactive oligonucleotide ligation assay to detect a common point mutation in the CYP2D6 gene causing abnormal drug metabolism

A new nonradioactive oligonucleotide ligation assay for the detection of a common point mutation in the CYP2D6 gene is presented. The assay takes advantage of simultaneous time-resolved fluorescence measurements of lanthanide-labeled probes and the specificity of T4-DNA ligase in combination with the polymerase chain reaction. This strategy makes it possible to perform the assay using both the wild-type-specific and mutant-specific probes simultaneously, securing an internal control in each reaction. We show that the allele-specific ligation part of the assay can be performed with great accuracy over a wide range of temperatures, salt concentrations, and T4-DNA ligase concentrations. This eliminates the risk of false-positive or false-negative reactions due to variations in these factors. Because the assay is simple to perform, is very reliable, and can be partly automated, we conclude that it is well-suited for analysis in a routine laboratory.

Robust nonradioactive oligonucleotide ligation assay to detect a common point mutation in the CYP2D6 gene causing abnormal drug metabolism

A new nonradioactive oligonucleotide ligation assay for the detection of a common point mutation in the CYP2D6 gene is presented. The assay takes advantage of simultaneous time-resolved fluorescence measurements of lanthanide-labeled probes and the specificity of T4-DNA ligase in combination with the polymerase chain reaction. This strategy makes it possible to perform the assay using both the wild-type-specific and mutant-specific probes simultaneously, securing an internal control in each reaction. We show that the allele-specific ligation part of the assay can be performed with great accuracy over a wide range of temperatures, salt concentrations, and T4-DNA ligase concentrations. This eliminates the risk of false-positive or false-negative reactions due to variations in these factors. Because the assay is simple to perform, is very reliable, and can be partly automated, we conclude that it is well-suited for analysis in a routine laboratory.

Serum lactate dehydrogenase isoenzyme 1. An early indicator of relapse in patients with testicular germ cell tumors

The present study aimed to evaluate serum lactate dehydrogenase isoenzyme 1 (S-LD-1) as an indicator of relapse for patients with testicular germ cell tumors. Twenty-seven patients were investigated with repeated determinations of S-LD-1 from diagnosis to relapse; 9 had seminoma and 18 nonseminomatous tumors. Eleven of 21 had raised S-LD-1 at relapse (4 with seminoma). Seven of the 27 patients had a raised S-LD-1 for median 2 months (1.4-4.5 months) before relapse was detected. Thus, S-LD-1 is of use, complementary to clinical examinations, determinations of serum alpha fetoprotein and human chorionic gonadotropin, and CT scans, in monitoring patients with testicular germ cell tumors for relapse.

An enzyme-linked immunosorbent assay for plasma-lactoferrin. Concentrations in 362 healthy, adult blood donors

Very different concentrations of plasma-lactoferrin in healthy adults have been reported in the literature. We compared three commercially available lactoferrins and lactoferrin purified in our laboratory as calibrators in an ELISA. No statistical differences among these preparations of lactoferrin were detected. The concentration of purified lactoferrin was measured by dry weight, and efforts were made in order to minimize loss of purified lactoferrin by adhesion to tubes etc. and thus, secure accuracy of the method. Dilutions were made in PBS 0.01 mol l-1 with NaCl 0.436 mol l-1, (NH4)2SO4 0.5 mol l-1, BSA 5 gl-1 and normal rabbit IgG 10 mg l-1, which was shown to give parallel dilution curves of primary calibrator, secondary calibrator and plasma samples. No significant difference in the content of lactoferrin in neutrophils (median; range) among men (1.78; 0.83-4.48 micrograms 10(-6) neutrophils; n = 20) and women (2.12; 1.16-9.30 micrograms 10(-6) neutrophils; n = 14) was found. Lactoferrin was analysed in EDTA-plasma obtained from 135 female and 227 male blood donors. Median concentrations were 84.7 and 97.8 micrograms l-1 respectively, while 2.5% and 97.5% reference limits (with 90% confidence intervals) were estimated to 42.9 (38.7-47.4) micrograms l-1 and 166.9 (151.0-186.3) micrograms l-1 for women and 52.3 (49.1-55.6) micrograms l-1 and 189.9 (175.9-206.4) micrograms l-1 for men, respectively.

Appropriate sera for calibration and control of specific protein assays

An ultracentrifugation technique is described which makes it possible to prepare protein calibrators and control sera which (i) are stable (more than 8 years documented for nine proteins), (ii) are clear (remains clear for more than 8 years at -80 degrees C), (iii) contain genuine proteins (documented electrophoretically and immunologically), and (iv) are reproducible to prepare (collection and preparation).

Discrepancy in HbA1c measurements performed at different local laboratories and at a selected central reference laboratory

As participants in a general practice intervention study, 66 patients had their HbA1c measured both at a local and at a selected central reference laboratory. A discrepancy in the results was observed, as 97% of the results measured locally were lower than the centrally determined results. Bias (as calculated from mean value of measured HbA1c) between local laboratories and the central laboratory was measured to -1.47% HbA1c. A bias of this magnitude gave "problems" both to the general practitioners, patients and laboratories. To reduce the "problems" a bias of 0.5% HbA1c is estimated to be acceptable. But, to avoid these "problems" totally, a bias of 0.25% HbA1c is estimated to be the highest allowed bias. For HbA1c, a control system for both control of method standardisation and for specificity is described.

Analytical bias by contamination from hemolysis in determination of serum lactate dehydrogenase isoenzyme 1 in patients with testis germ cell tumors

We investigated the impact of correction for contamination from hemolysis on serum lactate dehydrogenase isoenzyme 1 (S-LD-1) determinations. A study of hemolysates from 7 control patients showed a mean correction factor for the contamination of 0.1 U/L S-LD-1 for each 1 mg/L serum hemoglobin (S-Hb). S-LD-1 in a series of blood samples from 44 patients (EJC 1992;28:410-5) would decrease median 24 U/L (range 8-70 U/L) if the measurements were corrected with this factor. So we advice to correct S-LD-1 determinations for the contamination with a common correction based on the S-Hb concentrations in the samples.

A Nordic reference serum suitable for use as trueness control in the clinical routine laboratory

The described reference serum is characterized by: liquid human serum at "normal" level stored in frozen state at -80 degrees C; minimum damage of proteins; aseptic preparation; cryoprecipitate and excess fibrin removed; serum cleared by ultracentrifugation; pH at 7.2-7.6; available in sealed glass ampoules with inert gas (one ml serum in each); specified components among most frequently analyzed analytes; homogeneity assured and stability monitored; produced under strict rules for good manufacturing practices (GMP). The assigned values are traceable to reference measurement procedures and reference materials of highest achievable metrological level; according to the present proposal the maximum allowable uncertainty of the assigned value is based on biological variation (shared common reference intervals); the uncertainty should ideally not exceed 1/5 of the maximum allowable bias of results obtained on patients samples (even 1/2 would theoretically be acceptable and, for a practical guide approximately < 1% may suffice). The present document provides some guidance of how the reference serum could be established in practice. The document also indicates the use of the material and further extension of the concept. The present work is done as a NORDKEM project.

External analytical quality assurance for proteins

In the Nordic Protein Project an external control scheme (external quality assessment) was combined with the two other indispensable aspects of analytical quality, i.e. standardization (with a common high quality calibrator) and specification of needed analytical quality for sharing common reference intervals for nine serum proteins in the Nordic countries. The quality specifications are reliable for the purpose and given in clinical chemical terms--ready for application to the control systems. Further, a control design for disclosing external and internal errors, separately, is designed with respect to calibration and robustness towards analytical interference from turbid patient samples.

A programme for assigning target values for external quality assessment schemes in countries with no authorized reference laboratories. Annex. Experiences with deviating results on Ektachem 700 XR

The use of consensus values in external quality assessment schemes (EQAS) involves several problems and should preferably be replaced with target values obtained by methods of high metrological level. However, such values are difficult to obtain. In the present study we transferred values from the NIST (former NBS) certified reference serum SRM 909 to lyophilized and frozen test sera for various inorganic components using flame absorption or flame emission spectrometry. Enzyme values were assigned by laboratories of members of the former Scandinavian Enzyme Committee. The assignment was based on 2-4 determinations each day through 3 days of experiment. A total of 10 laboratories participated in the work. The results were utilized in a Danish EQAS. One practical concern is the fairly long time (9 months) which was needed for production, collection and compiling all data. To get an impression of how much dry chemistry analysers, e.g, could influence consensus values a Kodak Ektachem 700 XR was studied using lyophilized and frozen sera. The results are reported in the annex. On NIST SRM 909 the values found for sodium(I) were 6% too high even though the findings on frozen human sera were accurate. For aspartate aminotransferase a result three times the target values was found on a human lyophilized serum, while the values on the frozen sera only were slightly too high.

Serum lactate dehydrogenase isoenzyme 1 activity in patients with testicular germ cell tumors correlates with the total number of copies of the short arm of chromosome 12 in the tumor

The aim of our study was to assess the relationship between the serum lactate dehydrogenase isoenzyme 1 (S-LDH-1) activity in patients with testicular germ cell tumors and the number of copies of the short arm of chromosome 12 (12p) present in tumor. Twenty-seven adult patients with measurable tumor lesions were studied. Twenty-five had three or more copies of chromosome 12 per cell in the tumors. Nineteen had one or more copies of a specific chromosomal abnormality, an isochromosome of the short arm of chromosome 12, i(12p). Fourteen had increased S-LDH-1 levels. S-LDH-1 activity correlated significantly with the product of total tumor volume and the total number of copies of the short arm of chromosome 12 present per cell (total tumor 12p). We conclude that the total number of copies of the short arm of chromosome 12 in the tumors is most probably a factor contributing to the LDH-1 activity released from the tumors.

Serum lactate dehydrogenase isoenzyme 1 and tumour volume are indicators of response to treatment and predictors of prognosis in metastatic testicular germ cell tumours

44 patients with metastatic testicular germ cell tumours treated with cisplatin-based chemotherapy were evaluated for prognostic implications of clinical characteristics. 22 obtained complete remission by the initial chemotherapy, and 30 are disease-free. S-LDH-1 had an overall predictive value regarding the response of 80%, S-LDH of 64%, S-AFP of 62%, and S-hCG of 62%. In multivariate analysis regarding response, only tumour volume classified according to the Royal Marsden system (P = 0.0036) and S-LDH-1 (P = 0.0069) yielded information. Regarding survival, S-LDH-1 (P = 0.0141) and an estimate of total tumour mass (P = 0.0171) had most impact with additional information from S-hCG only (P = 0.0536). We conclude that S-LDH-1 may be used as a tumour marker in addition to S-hCG and S-AFP in patients with metastatic testicular germ cell tumour.

Screening for haemochromatosis: prevalence among Danish blood donors

Hereditary haemochromatosis is an autosomal recessive disease that is genetically expressed by excessive accumulation of iron in the tissues, resulting in cirrhosis, diabetes mellitus, cardiomyopathy and hypogonadism. As the disease may be diagnosed before the appearance of symptoms, and prevented by repeated phlebotomies, there are strong implications for adoption of a screening procedure. Determinations of transferrin saturation (TS) and serum ferritin concentration (SF) were used to screen 4302 blood donors, who were selected for follow-up studies if they fulfilled any of the following three criteria: (i) TS greater than or equal to 0.7; (ii) TS greater than or equal to 0.5 together with SF greater than or equal to 150 micrograms l-1; (iii) SF greater than or equal to 300 micrograms l-1. A total of 58 subjects who fulfilled at least one of these criteria were reinvestigated, after which 18 individuals still fulfilled at least one criterion. Fifteen subjects having SF greater than or equal to 300 micrograms l-1 were offered liver biopsy and thirteen of these accepted. In one individual, no stainable iron was detected, and two subjects did not fulfil the previously established diagnostic criteria for the diagnosis of hereditary haemochromatosis. Ten subjects who had a high TS and liver iron grade 2-4 according to Bassett were classified accordingly as homozygotes. On the basis of these results, the prevalence of haemochromatosis in Denmark was estimated to be 0.0037-0.0046.

Screening for haemochromatosis: influence of analytical imprecision, diagnostic limit and prevalence on test validity

Serum ferritin (S-ferritin) and the saturation of transferrin iron-binding capacity (TIBC-sat) were evaluated as screening procedures for idiopathic haemochromatosis in a non-diseased population. Special attention was paid to the influence of the analytical quality, but the effects of prevalence and discrimination limits were also considered. Changes in the analytical quality for S-ferritin and TIBC-sat used as single tests highly influenced the number of false test-positives. Increasing the coefficient of variation from 0.0 to 0.2 resulted in nearly a doubling of the number of false test-positives to be further investigated. Using even a high, yet achievable analytic quality with a low coefficient of variation of 0.056 and 0.059 for S-ferritin and TIBC-sat respectively, screening procedures had unacceptably high fractions of false test-positives and false test-negatives associated with any discrimination limit. If the prevalence of haemochromatosis is 0.003, the predictive value of a positive test result did not exceed 0.05, accepting a fraction of false test-negatives of 0.025. This was found to be too low for a screening test to be used in the general population. The combined use of S-ferritin and TIBC-sat resulted in higher performance with a sensitivity of 0.90, a specificity of 0.99 and a predictive value of a positive test result of 0.29 if a fraction of misclassification of 0.01 is accepted for each.

Analytical goal setting prior to selection of a method for glycated haemoglobin

Without a consensus on either a reference method or a single glycated haemoglobin standard, the individual laboratory has to establish and secure its own assay method. Prior to selection of a method for glycated haemoglobin we used an assessment model and defined our clinical goals. Based on clinical goals it was possible to set up goals of analytical quality and evaluate available literature concerning the performance characteristics of different assay methods. We wanted a method that measured HbAlc, without measuring the labile intermediate pre-HbAlc, and that provided separate detection of haemoglobin variants. Low imprecision was required to secure the measured, non-diabetic reference interval, and to minimize random analytical error. We found the isoelectric focusing method the only one able to meet our goals, and a method evaluation was carried out. Clinical goals of analytical quality should always be defined before method selection and implementation. Using this model, we were able to establish a precise isoelectric focusing method that fulfilled our clinical goals by measuring HbAlc with a total coefficient of variation of 2.1% and a non-diabetic reference interval from 5.2% to 6.8% HbAlc.