Calculating reference intervals for laboratory measurements

Discussion on the validity of commonly used reliability indices in sports medicine and exercise science: a critical review with data simulations

Apart from objectivity and validity, reliability is considered a precondition for testing within scientific works, as unreliable testing protocols limit conclusions, especially for practical application. Classification guidelines commonly refer to relative reliability, focusing on Pearson correlation coefficients (rp) and intraclass correlation coefficients (ICC). On those, the standard error of measurement (SEM) and the minimal detectable change (MDC) are often calculated in addition to the variability coefficient (CV). These, however, do not account for systematic or random errors (e.g., standardization problems). To illustrate, we applied common reliability statistics in sports science on simulated data which extended the sample size of two original counter-movement-jump sessions from (youth) elite basketball players. These show that excellent rp and ICC (≥ 0.9) without a systematic bias were accompanied by a mean absolute percentage error of over 20%. Furthermore, we showed that the ICC does not account for systematic errors and has only limited value for accuracy, which can cause misleading conclusions of data. While a simple re-organization of data caused an improvement in relative reliability and reduced limits of agreement meaningfully, systematic errors occurred. This example underlines the lack of validity and objectivity of commonly used ICC-based reliability statistics (SEM, MDC) to quantify the primary and secondary variance sources. After revealing several caveats in the literature (e.g., neglecting of the systematic and random error or not distinguishing between protocol and device reliability), we suggest a methodological approach to provide reliable data collections as a precondition for valid conclusions by, e.g., recommending pre-set acceptable measurement errors.

Stressing the Relevance of Differentiating between Systematic and Random Measurement Errors in Ultrasound Muscle Thickness Diagnostics

BACKGROUND

The majority of studies that explore changes in musculature following resistance training interventions or examine atrophy due to immobilization or sarcopenia use ultrasound imaging. While most studies assume acceptable to excellent reliability, there seems to be unawareness of the existing absolute measurement errors. As early as 1998, methodological research addressed a collective unawareness of the random measurement error and its practical indications. Referring to available methodological approaches, within this work, we point out the limited value of focusing on relative, correlation-based reliability indices for the interpretability in scientific research but also for clinical application by assessing 1,512 muscle thickness values from more than 400 ultrasound images. To account for intra- and inter-day repeatability, data were collected on two consecutive days within four testing sessions. Commonly-stated reliability values (ICC, CV, SEM and MDC) were calculated, while evidence-based agreement analyses were applied to provide the accompanied systematic and random measurement error.

RESULTS

While ICCs in the range of 0.832 to 0.998 are in accordance with the available literature, the mean absolute percentage error ranges from 1.34 to 20.38% and the mean systematic bias from 0.78 to 4.01 mm (all p ≤ 0.013), depending on the measurement time points chosen for data processing.

CONCLUSIONS

In accordance with prior literature, a more cautious interpretation of relative reliability values should be based on included systematic and random absolute measurement scattering. Lastly, this paper discusses the rationale for including different measurement error statistics when determining the validity of pre-post changes, thus, accounting for the certainty of evidence.

A Bayesian nonparametric meta-analysis model for estimating the reference interval

A reference interval represents the normative range for measurements from a healthy population. It plays an important role in laboratory testing, as well as in differentiating healthy from diseased patients. The reference interval based on a single study might not be applicable to a broader population. Meta-analysis can provide a more generalizable reference interval based on the combined population by synthesizing results from multiple studies. However, the assumptions of normally distributed underlying study-specific means and equal within-study variances, which are commonly used in existing methods, are strong and may not hold in practice. We propose a Bayesian nonparametric model with more flexible assumptions to extend random effects meta-analysis for estimating reference intervals. We illustrate through simulation studies and two real data examples the performance of our proposed approach when the assumptions of normally distributed study means and equal within-study variances do not hold.

Rectangular multivariate normal prediction regions for setting reference regions in laboratory medicine

Reference intervals are among the most widely used medical decision-making tools and are invaluable in the interpretation of laboratory results of patients. Moreover, when multiple biochemical analytes are measured on each patient, a multivariate reference region (MRR) is needed. Such regions are more desirable than separate univariate reference intervals since the latter disregard the cross-correlations among variables. Traditionally, assuming multivariate normality, MRRs have been constructed as ellipsoidal regions, which cannot detect componentwise extreme values. Consequently, MRRs are rarely used in actual practice. In order to address the above drawback of ellipsoidal reference regions, we propose a procedure to construct rectangular MRRs under multivariate normality. The rectangular MRR is computed using a prediction region criterion. However, since the population correlations are unknown, a parametric bootstrap approach is employed for computing the required prediction factor. Also addressed in this study is the computation of mixed reference intervals, which include both two-sided and one-sided prediction limits, simultaneously. Numerical results show that the parametric bootstrap procedure is quite accurate, with estimated coverage probabilities very close to the nominal level. Moreover, the expected volumes of the proposed rectangular regions are substantially smaller than the expected volumes obtained from Bonferroni simultaneous prediction intervals. We also explore the computation of covariate-dependent MRRs in a multivariate regression setting. Finally, we discuss real-life applications of the proposed methods, including the computation of reference ranges for the assessment of kidney function and for components of the insulin-like growth factor system in adults.

Rectangular tolerance regions and multivariate normal reference regions in laboratory medicine

Reference intervals are widely used in the interpretation of results of biochemical and physiological tests of patients. When there are multiple biochemical analytes measured from each subject, a multivariate reference region is needed. Because of their greater specificity against false positives, such reference regions are more desirable than separate univariate reference intervals that disregard the cross-correlations between variables. Traditionally, under multivariate normality, reference regions have been constructed as ellipsoidal regions. This approach suffers from a major drawback: it cannot detect component-wise extreme observations. In the present work, procedures are developed to construct rectangular reference regions in the multivariate normal setup. The construction is based on the criteria for tolerance intervals. The problems addressed include the computation of a rectangular tolerance region and simultaneous tolerance intervals. Also addressed is the computation of mixed reference intervals that include both two-sided and one-sided limits, simultaneously. A parametric bootstrap approach is used in the computations, and the accuracy of the proposed methodology is assessed using estimated coverage probabilities. The problem of sample size determination is also addressed, and the results are illustrated using examples that call for the computation of reference regions.

Determination of Perceived Levels of Physical Work Demand Thresholds, and Reliability and Responsiveness of the Modified-Spinal Function Sort Questionnaire in a Multidisciplinary Occupational Rehabilitation Setting

PURPOSE

To determine the levels of perceived work demand capacity corresponding to the Modified Spinal Function Sort (M-SFS) score and precise reliability validity and responsiveness.

METHODS

This prospective validation study included patients with chronic musculoskeletal impairments who underwent multidisciplinary occupational rehabilitation. After determining the percentiles of the work demand thresholds corresponding to the spinal function sort (SFS), the percentiles were transposed to the M-SFS. Reliability was assessed using the intraclass correlation coefficient and limits of agreement. Correlations with other questionnaires and a lifting task were measured to assess validity. Responsiveness was determined using anchor- and distribution-based approaches.

RESULTS

288 patients were included. The following thresholds were obtained for the M-SFS: 0-43 points, minimal; 44-50, very light; 51-58, light; 59-64, light to medium; 65-70, medium; 71-76, heavy; and 77-80, very heavy. Reliability was confirmed. The correlation between the M-SFS and SFS scores was good at 0.89 (95% CI, 0.86-0.91) and moderate according to the PILE-test result of 0.60 (95% CI, 0.50-0.67). We could not calculate a valid anchor-based minimal clinically important difference. The standard error of measurement was 3.9 points, and the smallest detectable change was 10.8 points.

CONCLUSIONS

On the basis of the comparison of the M-SFS and SFS scores, the M-SFS score can be interpreted in relation to the levels of work demand. This study confirms the good reliability and validity of the M-SFS questionnaire in assessing perceived physical capacity. Further studies are needed to determine its responsiveness.

Determinants and Reference Ranges of Serum Immunoglobulins in Middle-Aged and Elderly Individuals: a Population-Based Study

Purpose

In clinical practice, currently one reference range for serum immunoglobulin (Ig) A, G, and M is applied to all adults, although various factors may influence Ig serum levels. Population-based data on determinants of IgA, IgG, and IgM and recommendations for subgroup specific reference ranges are lacking. We aimed to provide an overview of determinants of IgA, IgG, and IgM in community-dwelling middle-aged and elderly individuals and explore determinants that influence Ig reference ranges.

Methods

Within the Rotterdam Study, we performed linear regression analyses for the association of demographic, lifestyle, and cardiovascular factors with serum IgA, IgG, and IgM. We furthermore calculated Ig reference ranges (based on percentiles), both overall and within relevant subgroups.

Results

We included 8768 participants (median age 62 years). IgA and IgG increased non-linearly with higher age (P < .0001 for both). Women had lower IgA (beta: − 0.24; 95% confidence interval [95% CI]: − 0.29; − 0.20) and IgG (beta: − 0.33; 95% CI: − 0.44; − 0.23), but higher IgM levels (beta: 0.08; 95% CI: 0.04;0.13) than men. Former and particularly current smoking were associated with lower IgA and IgG (betas between − 0.07 and − 1.03). Higher alcohol consumption was associated with lower IgG (beta for heavy drinking: − 0.70; 95% CI: − 0.91; − 0.48). Corticosteroid use was associated with lower IgG (beta: − 1.12; 95% CI: − 1.58; − 0.66). Associations with cardiovascular factors were heterogeneous and differed between sexes.

Conclusion

Age, sex, smoking, alcohol consumption, corticosteroid use, and cardiovascular factors are determinants that should be considered when interpreting serum Ig levels in middle-aged and elderly individuals and may require adjusted reference ranges.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01120-5.

Modeling conditional reference regions: Application to glycemic markers

Many clinical decisions are taken based on the results of continuous diagnostic tests. Usually, only the results of one single test is taken into consideration, the interpretation of which requires a reference range for the healthy population. However, the use of two different tests, can be necessary in the diagnosis of certain diseases. This obliges a bivariate reference region be available for their interpretation. It should also be remembered that reference regions may depend on patient variables (eg, age and sex) independent of the suspected disease. However, few proposals have been made regarding the statistical modeling of such reference regions, and those put forward have always assumed a Gaussian distribution, which can be rather restrictive. The present work describes a new statistical method that allows such reference regions to be estimated with no insistence on the results being normally distributed. The proposed method is based on a bivariate location-scale model that provides probabilistic regions covering a specific percentage of the bivariate data, dependent on certain covariates. The reference region is estimated nonparametrically and the nonlinear effects of continuous covariates via polynomial kernel smoothers in additive models. The bivariate model is estimated using a backfitting algorithm, and the optimal smoothing parameters of the kernel smoothers selected by cross-validation. The model performed satisfactorily in simulation studies under the assumption of non-Gaussian conditions. Finally, the proposed methodology was found to be useful in estimating a reference region for two continuous diagnostic tests for diabetes (fasting plasma glucose and glycated hemoglobin), taking into account the age of the patient.

Physiological vital sign reference ranges for well late preterm newborns calculated during a typical two-hour newborn period between 2 hours and 7 days of life

Objectives To calculate 95% reference ranges for heart rate, respiratory rate, oxygen saturation, temperature and blood pressure for well late preterm newborns between 34+0/7 and 36+6/7 weeks of gestation during typical neonatal behaviour. Approach A single site, prospective cohort study in a major Australian quaternary hospital between February and September 2019. A total of 120 late preterm newborns had their heart rate, respiratory rate and oxygen saturation measurements recorded every two seconds for up to two hours with unconditional 95% reference ranges determined using a linear mixed model with random intercept for total standard deviation calculation including repeated measures. Temperature and blood pressure measurements were collected twice - at the start and conclusion of the data recording period, with weighted 2.5th and 97.5th percentiles calculated using the mean value. Main results A total of 364,577 heart rate, 365,208 respiratory rate, 360,494 peripheral oxygen saturation, and 240 temperature and blood pressure values were obtained. The 95% reference ranges were: heart rate 102 - 164 bpm; respiratory rate 15 - 67 rpm; oxygen saturation 94 - 100%; temperature 36.4 - 37.6°C; systolic blood pressure 51 - 86 mmHg; diastolic blood pressure 28 - 61 mmHg; mean arterial pressure 35 - 68 mmHg. Significance Seven vital sign references ranges were reported for the late preterm population during a typical newborn period (such as crying, sleeping, feeding, awake and alert, and during nappy hygiene cares); internal and external validation should be completed prior to clinical use. Cut off points for escalation of care have previously been generalised to all newborns irrespective of gestational age which may result in over-treatment or a delay in recognising subtle signs of deterioration.

Disease-associated reference intervals for twenty laboratory tests in patients with rheumatoid arthritis, Crohn's disease or ulcerative colitis

BACKGROUND

Population based reference intervals are fundamental for interpreting results for quantitative laboratory tests. In patients with a specific chronic disorder, however, results of various tests may regularly be different than in healthy individuals. Health-associated reference intervals may therefore have limited value in such patients. Instead, disease-associated reference intervals may be useful, as they describe the results distribution in populations resembling the specific patients. Few disease-associated reference intervals are available in the literature. The aim of this study was to estimate reference intervals for common laboratory tests for patient populations with rheumatoid arthritis, Crohn's disease or ulcerative colitis without significant comorbidity, using a novel algorithm.

MATERIAL AND METHODS

Laboratory test results and hospital discharge diagnoses were collected for relevant patients. An algorithm was developed to identify discharge diagnoses significantly associated with high or low results for specific tests. After excluding patients with such diagnoses, reference intervals were estimated, representing results distributions in patients with each of the specific chronic disorders, but without significant comorbidity.

RESULTS

Disease-associated reference intervals were estimated for 20 common laboratory tests. Most of the estimated reference limits were significantly different from corresponding health-associated reference limits. Thirty percent of the estimated reference intervals were different from estimates based on crude patient populations, indicating that the algorithm applied managed to exclude patients with relevant comorbidity.

CONCLUSION

Disease-associated reference intervals could be estimated for a number of tests in patients with rheumatoid arthritis, ulcerative colitis or Crohn's disease using a highly automated algorithm based on routinely recorded patient data.

Fluorescence-Based Ratiometric Analysis of Sperm Centrioles (FRAC) Finds Patient Age and Sperm Morphology Are Associated With Centriole Quality

A large proportion of infertility and miscarriage causes are unknown. One potential cause is a defective sperm centriole, a subcellular structure essential for sperm motility and embryonic development. Yet, the extent to which centriolar maladies contribute to male infertility is unknown due to the lack of a convenient way to assess centriole quality. We developed a robust, location-based, ratiometric assay to overcome this roadblock, the Fluorescence-based Ratiometric Assessment of Centrioles (FRAC). We performed a case series study with semen samples from 33 patients, separated using differential gradient centrifugation into higher-grade (pellet) and lower-grade (interface) sperm fractions. Using a reference population of higher-grade sperm from infertile men with morphologically standard sperm, we found that 79% of higher-grade sperm of infertile men with substandard sperm morphology have suboptimal centrioles (P = 0.0005). Moreover, tubulin labeling of the sperm distal centriole correlates negatively with age (P = 0.004, R = -0.66). These findings suggest that FRAC is a sensitive method and that patient age and sperm morphology are associated with centriole quality.

Nonparametric hyperrectangular tolerance and prediction regions for setting multivariate reference regions in laboratory medicine

Reference regions are widely used in clinical chemistry and laboratory medicine to interpret the results of biochemical or physiological tests of patients. There are well-established methods in the literature for reference limits for univariate measurements; however, limited methods are available for the construction of multivariate reference regions, since traditional multivariate statistical regions (e.g. confidence, prediction, and tolerance regions) are not constructed based on a hyperrectangular geometry. The present work addresses this problem by developing multivariate hyperrectangular nonparametric tolerance regions for setting the reference regions. The approach utilizes statistical data depth to determine which points to trim and then the extremes of the trimmed dataset are used as the faces of the hyperrectangular region. Also presented is a strategy for determining the number of points to trim based on previously established asymptotic results. An extensive coverage study shows the favorable performance of the proposed procedure for moderate to large sample sizes. The procedure is applied to obtain reference regions for addressing two important clinical problems: (1) assessing kidney function in adolescents and (2) characterizing insulin-like growth factor concentrations in the serum of adults.

Reference Values for 30 Common Biochemistry Analytes Across 5 Different Analyzers in Neonates and Children 30 Days to 18 Years of Age

BACKGROUND

Age-specific reference intervals (RIs) have been developed for biochemistry analytes in children. However, the ability to interpret results from multiple laboratories for 1 individual is limited. This study reports a head-to-head comparison of reference values and age-specific RIs for 30 biochemistry analytes for children across 5 analyzer types.

METHODS

Blood was collected from healthy newborns and children 30 days to &lt;18 years of age. Serum aliquots from the same individual were analyzed on 5 analyzer types. Differences in the mean reference values of the analytes by the analyzer types were investigated using mixed-effect regression analysis and by comparing maximum variation between analyzers with analyte-specific allowable total error reported in the Westgard QC database. Quantile regression was used to estimate age-specific RIs using power variables in age selected by fractional polynomial regression for the mean, with modification by sex when appropriate.

RESULTS

The variations of age-specific mean reference values between analyzer types were within allowable total error (Westgard QC) for most analytes, and common age-specific reference limits were reported as functions of age and/or sex. Analyzer-specific reference limits for all analytes on 5 analyzer types are also reported as functions of age and/or sex.

CONCLUSIONS

This study provides quantitative and qualitative measures of the extent to which results for individual children can or cannot be compared across analyzer types, and the feasibility of RI harmonization. The reported equations enable incorporation of age-specific RIs into laboratory information systems for improving evidence-based clinical decisions in children.

Right ventricular total isovolumic time: Reference value study

BACKGROUND

There is lack of noninvasive indices to detail the right side cardiovascular physiology. Total isovolumic time (tIVT) is a sensitive marker of left ventricular electromechanical efficiency and systolic-diastolic interaction. The aim of the study was to evaluate normal reference value of the right ventricular tIVT with increasing age.

METHODS AND RESULTS

One hundred and eighty-one healthy volunteers (51% male) underwent transthoracic echocardiography. The population was divided into four categories according to age: A < 30 years; B 30-39 years; C 40-49 years; and C ≥ 50 years old. tIVT was computed in seconds/minutes as: 60 - (tET + tFT). tET and tFT are the total ejection and filling time adjusted by the heart rate, measured, respectively, from the onset to the end of the right ventricle (RV) forward flow through the pulmonary valve and from the onset of the E-wave and the end of the A-wave at the level of the tricuspid valve. The mean RV tIVT was 7 ± 1.1 s/min and increased significantly with age, from a 3.4 to 9.7 s/min(P < 0.0001). Significant correlation was found between tIVT and trans-tricuspid E/E' (P < 0.0001; 0.78 (95% CI: 0.715-0.831) while weaker between tIVT and E/A (P = 0.001; -0.283 95% CI: -0.413 to -0.143).

CONCLUSION

The normal values of RV tIVT increase with age and correlate significantly with Doppler diastolic parameters.

Design and other methodological considerations for the construction of human fetal and neonatal size and growth charts

This paper discusses the features of study design and methodological considerations for constructing reference centile charts for attained size, growth, and velocity charts with a focus on human growth charts used during pregnancy. Recent systematic reviews of pregnancy dating, fetal size, and newborn size charts showed that many studies aimed at constructing charts are still conducted poorly. Important design features such as inclusion and exclusion criteria, ultrasound quality control measures, sample size determination, anthropometric evaluation, gestational age estimation, assessment of outliers, and chart presentation are seldom well addressed, considered, or reported. Many of these charts are in clinical use today and directly affect the identification of at‐risk newborns that require treatment and nutritional strategies.

This paper therefore reiterates some of the concepts previously identified as important for growth studies, focusing on considerations and concepts related to study design, sample size, and methodological considerations with an aim of obtaining valid reference or standard centile charts. We discuss some of the key issues and provide more details and practical examples based on our experiences from the INTERGROWTH‐21^st Project. We discuss the statistical methodology and analyses for cross‐sectional studies and longitudinal studies in a separate article in this issue.

Current Issues in the Development of Foetal Growth References and Standards

PURPOSE OF REVIEW

This paper discusses the current issues in the development of foetal charts and is informed by a scoping review of studies constructing charts between 2012 and 2018.

RECENT FINDINGS

The scoping review of 20 articles revealed that there is still a lack of consensus on how foetal charts should be constructed and whether an international chart that can be applied across populations is feasible. Many of these charts are in clinical use today and directly affect the identification of at risk newborns that require treatment and nutritional strategies. However, there is no agreement on important design features such as inclusion and exclusion criteria; sample size and agreement on definitions such as what constitutes a healthy population of pregnant women that can be used for constructing foetal standards.

SUMMARY

This paper therefore reiterates some of these current issues and the scoping review showcases the heterogeneity in the studies developing foetal charts between 2012 and 2018. There is no consensus on these pertinent issues and hence if not resolved will lead to continued surge of foetal reference and standard charts which will only exacerbate the current problem of not being able to make direct comparisons of foetal size and growth across populations.

Spleen size evaluation in children: Time to define splenomegaly for pediatric surgeons and pediatricians

BACKGROUND

We determined the range of normal spleen dimensions evaluated by ultrasonography (US) in children according to sex and age and the relationship between splenic measurements, auxological data and body proportions, in order to define splenomegaly parameters in support of the surgical mini-invasive approaches in pediatrics.

METHODS

We prospectively examined 317 caucasian children of both sexes. The patients were divided into three groups: 0-3 years; 4-10 years; 11-18 years. Sex, weight, height/length, body mass index (BMI), waist circumference and xipho-pubic distance were determined for each child. US spleen evaluation included longitudinal/antero-posterior/transverse diameters, transverse area and volume. Spleen volume/abdominal volume, longitudinal spleen diameter/longitudinal left kidney diameter and longitudinal spleen diameter/xipho-pubic distance ratios were also calculated.

RESULTS

For caucasian subjects, in different age groups spleen volume, transverse area and diameter increased while the spleen/abdominal volume ratio decreased significantly (p<0.001). A significant (p<0.001) decrease in longitudinal spleen diameter/xipho-pubic distance ratio was noted between the 0-3 years group and both 4-10 and 11-18 years group. Age and auxological data, except BMI, showed a high correlation with spleen dimension (r≥0.8).

CONCLUSIONS

The current concept of splenomegaly is not applicable in pediatric surgery. A dedicated classification of splenomegaly is needed for children and would improve the safety and feasibility of treatment.

Precise confidence intervals of regression-based reference limits: Method comparisons and sample size requirements

Covariate-dependent reference limits have been extensively applied in biology and medicine for determining the substantial magnitude and relative importance of quantitative measurements. Confidence interval and sample size procedures are available for studying regression-based reference limits. However, the existing popular methods employ different technical simplifications and are applicable only in certain limited situations. This paper describes exact confidence intervals of regression-based reference limits and compares the exact approach with the approximate methods under a wide range of model configurations. Using the ratio between the widths of confidence interval and reference interval as the relative precision index, optimal sample size procedures are presented for precise interval estimation under expected ratio and tolerance probability considerations. Simulation results show that the approximate interval methods using normal distribution have inaccurate confidence limits. The exact confidence intervals dominate the approximate procedures in one- and two-sided coverage performance. Unlike the current simplifications, the proposed sample size procedures integrate all key factors including covariate features in the optimization process and are suitable for various regression-based reference limit studies with potentially diverse configurations. The exact interval estimation has theoretical and practical advantages over the approximate methods. The corresponding sample size procedures and computing algorithms are also presented to facilitate the data analysis and research design of regression-based reference limits.

A retrospective analysis of biochemical and haematological parameters in patients with eating disorders

BACKGROUND

The objective of the study was to determine whether levels of biochemical and haematological parameters in patients with eating disorders (EDs) varied from the general population. Whilst dietary restrictions can lead to nutritional deficiencies, specific abnormalities may be relevant to the diagnosis, pathogenesis and treatment of EDs.

METHODS

With ethics approval and informed consent, a retrospective chart audit was conducted of 113 patients with EDs at a general practice in Brisbane, Australia. This was analysed first as a total group (TG) and then in 4 ED subgroups: Anorexia nervosa (AN), Bulimia nervosa (BN), ED Not Otherwise Specified (EDNOS), and AN/BN. Eighteen parameters were assessed at or near first presentation: cholesterol, folate, vitamin B12, magnesium, manganese, zinc, calcium, potassium, urate, sodium, albumin, phosphate, ferritin, vitamin D, white cell count, neutrophils, red cell count and platelets. Results were analysed using IBM SPSS 21 and Microsoft Excel 2013 by two-tailed, one-sample t-tests (TG and 4 subgroups) and chi-square tests (TG only) and compared to the population mean standards. Results for the TG and each subgroup individually were then compared with the known reference interval (RI).

RESULTS

For the total sample, t-tests showed significant differences for all parameters (p < 0.05) except cholesterol. Most parameters gave results below population levels, but folate, phosphate, albumin, calcium and vitamin B12 were above. More patients than expected were below the RI for most parameters in the TG and subgroups.

CONCLUSIONS

At diagnosis, in patients with EDs, there are often significant differences in multiple haematological and biochemical parameters. Early identification of these abnormalities may provide additional avenues of ED treatment through supplementation and dietary guidance, and may be used to reinforce negative impacts on health caused by the ED to the patient, their family and their treatment team (general practitioner, dietitian and mental health professionals). Study data would support routine measurement of a full blood count and electrolytes, phosphate, magnesium, liver function tests, ferritin, vitamin B12, red cell folate, vitamin D, manganese and zinc for all patients at first presentation with an ED.

Reference curves for the Australian/Canadian Hand Osteoarthritis Index in the middle-aged Dutch population

Objective

The aim was to establish reference curves of the Australian/Canadian Hand Osteoarthritis Index (AUSCAN), a widely used questionnaire assessing hand complaints.

Methods

Analyses were performed in a population-based sample, The Netherlands Epidemiology of Obesity study (n = 6671, aged 45-65 years). Factors associated with AUSCAN scores were analysed with ordered logistic regression, because AUSCAN data were zero inflated, dividing AUSCAN into three categories (0 vs 1-5 vs >5). Age- and sex-specific reference curves for the AUSCAN (range 0-60; higher is worse) were developed using quantile regression in conjunction with fractional polynomials. Observed scores in relevant subgroups were compared with the reference curves.

Results

The median age was 56 [interquartile range (IQR): 50-61] years; 56% were women and 12% had hand OA according to ACR criteria. AUSCAN scores were low (median 1; IQR: 0-4). Reference curves where higher for women, and increased moderately with age: 95% percentiles for AUSCAN in men and women were, respectively, 5.0 and 12.3 points for a 45-year-old, and 15.2 and 33.6 points for a 65-year-old individual. Additional associated factors included hand OA, inflammatory rheumatic diseases, FM, socio-economic status and BMI. Median AUSCAN pain subscale scores of women with hand OA lay between the 75th and 90th centiles of the general population.

Conclusion

AUSCAN scores in the middle-aged Dutch population were low overall, and higher in women than in men. AUSCAN reference curves could serve as a benchmark in research and clinical practice settings. However, the AUSCAN does not measure hand complaints specific for hand OA.

Prevalence of sarcopenia in community-dwelling older people of Mexico City using the EGWSOP (European Working Group on Sarcopenia in Older People) diagnostic criteria

Background: The aim of this study is to determine the prevalence of sarcopenia in community-dwelling older people living in Mexico City using the EGWSOP (European Working Group on Sarcopenia in Older People) diagnostic criteria that include muscle mass, muscle strength and physical performance.Methods: The sample population was based on older people (≥60 years) affiliated with the Mexican Institute of Social Security in Mexico City. Data were derived from the database of the “Cohort of Obesity, Sarcopenia and Frailty of Older Mexican Adults” (COSFOMA). Sarcopenia was diagnosed using the EGWSOP criteria: gait speed (4 m) <0.8 m/s; handgrip strength (using a dynamometer) <20 kg in females or <30 kg in males, and muscle mass index (MMI) <6.1 kg/m2 in females or <8.5 kg/m2 in males (using bioimpedance analysis).Results: Thousand hundred seventy-seven subjects were included (median age 68.4 years, 60.2% females). 20.5% had low gait speed (19.1% females and 22.6% males); 62.4% had low handgrip strength (69.9% females and 51.2% males) and 12.3% had low muscle mass (9.9% females and 16.0% males). Only 9.9% of older people with sarcopenia (9.0% females and 11.1% males): 1.9% with severe sarcopenia (1.4% females and 2.6% males) and 8.0% with moderate sarcopenia (7.6% females and 8.5% males).Conclusions: Sarcopenia is present in one of ten community-dwelling older people residing in Mexico City. According to what has been reported in the literature, the prevalence of sarcopenia in older Mexican adults is similar to the community-dwelling population.

Gestation-specific reference intervals for comprehensive spot urinary steroid hormone metabolite analysis in normal singleton pregnancy and 6 weeks postpartum

BACKGROUND

Normal pregnancy depends on pronounced adaptations in steroid hormone concentrations. Although in recent years, the understanding of these hormones in pregnancy has improved, the interpretation is hampered by insufficient reference values. Our aim was to establish gestation-specific reference intervals for spot urinary steroid hormone levels in normal singleton pregnancies and 6 weeks postpartum.

METHODS

Cross-sectional multicentre observational study. Women recruited between 2008 and 2013 at 3 University Hospitals in Switzerland (Bern), Scotland (Glasgow) and Austria (Graz). Spot urine was collected from healthy women undergoing a normal pregnancy (age, 16-45 years; mean, 31 years) attending routine antenatal clinics at gestation weeks 11, 20, and 28 and approximately 6 weeks postpartum. Urine steroid hormone levels were analysed using gas-chromatography mass spectrometry. Creatinine was also measured by routine analysis and used for normalisation.

RESULTS

From the results, a reference interval was calculated for each hormone metabolite at each trimester and 6 weeks postpartum. Changes in these concentrations between trimesters and postpartum were also observed for several steroid hormones and followed changes proposed for index steroid hormones.

CONCLUSIONS

Normal gestation-specific reference values for spot urinary steroid hormones throughout pregnancy and early postpartum are now available to facilitate clinical management and research approaches to steroid hormone metabolism in pregnancy and the early postpartum period.

A Population-Based Model to Consider the Effect of Seasonal Variation on Serum 25(OH)D and Vitamin D Status

Background. We elaborated a model that predicts the centiles of the 25(OH)D distribution taking into account seasonal variation. Methods. Data from two Swiss population-based studies were used to generate (CoLaus) and validate (Bus Santé) the model. Serum 25(OH)D was measured by ultra high pressure LC-MS/MS and immunoassay. Linear regression models on square-root transformed 25(OH)D values were used to predict centiles of the 25(OH)D distribution. Distribution functions of the observations from the replication set predicted with the model were inspected to assess replication. Results. Overall, 4,912 and 2,537 Caucasians were included in original and replication sets, respectively. Mean (SD) 25(OH)D, age, BMI, and % of men were 47.5 (22.1) nmol/L, 49.8 (8.5) years, 25.6 (4.1) kg/m², and 49.3% in the original study. The best model included gender, BMI, and sin-cos functions of measurement day. Sex- and BMI-specific 25(OH)D centile curves as a function of measurement date were generated. The model estimates any centile of the 25(OH)D distribution for given values of sex, BMI, and date and the quantile corresponding to a 25(OH)D measurement. Conclusions. We generated and validated centile curves of 25(OH)D in the general adult Caucasian population. These curves can help rank vitamin D centile independently of when 25(OH)D is measured.

Hearing Impairment in Relation to Severity of Diabetes in a Veteran Cohort

OBJECTIVE

Type 2 diabetes is epidemic among veterans, approaching three times the prevalence of the general population. Diabetes leads to devastating complications of vascular and neurologic malfunction and appears to impair auditory function. Hearing loss prevention is a major health-related initiative in the Veterans Health Administration. Thus, this research sought to identify, and quantify with effect sizes, differences in hearing, speech recognition, and hearing-related quality of life (QOL) measures associated with diabetes and to determine whether well-controlled diabetes diminishes the differences.

DESIGN

The authors examined selected cross-sectional data from the baseline (initial) visit of a longitudinal study of Veterans with and without type 2 diabetes designed to assess the possible differences in age-related trajectories of peripheral and central auditory function between the two groups. In addition, the diabetes group was divided into subgroups on the basis of medical diagnosis of diabetes and current glycated hemoglobin (HbA1c) as a metric of disease severity and control. Outcome measures were pure-tone thresholds, word recognition using sentences presented in noise or time-compressed, and an inventory assessing the self-perceived impact of hearing loss on QOL. Data were analyzed from 130 Veterans ages 24 to 73 (mean 48) years with well-controlled (controlled) diabetes, poorly controlled (uncontrolled) diabetes, prediabetes, and no diabetes. Regression was used to identify any group differences in age, noise exposure history, and other sociodemographic factors, and multiple regression was used to model each outcome variable, adjusting for potential confounders. Results were evaluated in relation to diabetes duration, use of insulin (yes, no), and presence of selected diabetes complications (neuropathy and retinopathy).

RESULTS

Compared with nondiabetics, Veterans with uncontrolled diabetes had significant differences in hearing at speech frequencies, including poorer hearing by 3 to 3.5 dB for thresholds at 250 Hz and in a clinical pure-tone average, respectively. Compared with nondiabetic controls, individuals with uncontrolled diabetes also significantly more frequently reported that their hearing adversely impacted QOL on one of the three subscales (ability to adapt). Despite this, although they also had slightly poorer mean scores on both word recognition tasks performed, these differences did not reach statistical significance and all subjects performed well on these tasks. Compared with Veterans with controlled diabetes, those with uncontrolled disease tended to have had diabetes longer, be insulin-dependent, and have a greater prevalence of diabetic retinopathy. Results are generally comparable with the literature with regard to the magnitude of threshold differences and the prevalence of hearing impairment but extend prior work by providing threshold difference and hearing loss prevalence effect sizes by category of diabetes control and by including additional functional measures.

CONCLUSIONS

In a cohort of Veterans with type 2 diabetes and relatively good hearing, significant effects of disease severity were found for hearing thresholds at a subset of frequencies and for one of the three QOL subscales. Significant differences were concentrated among those with poorly controlled diabetes based on current HbA1c. Results provide evidence that the observed hearing dysfunction in type 2 diabetes might be prevented or delayed through tight metabolic control. Findings need to be corroborated using longitudinal assessments.

The statistical basis for serial monitoring in audiology

OBJECTIVES

Audiologists regularly use serial monitoring to evaluate changes in a patient's auditory function over time. Observed changes are compared with reference standards to determine whether further clinical action is necessary. Reference standards are established in a control sample of otherwise healthy subjects to identify the range of auditory shifts that one might reasonably expect to occur in the absence of any pathological insult. Statistical approaches to this seemingly mundane problem typically invoke 1 of 3 approaches: percentiles of the cumulative distribution, the variance of observed shifts, and the "standard error of measurement." In this article, the authors describe the statistical foundation for these approaches, along with a mixed model-based alternative, and identify several necessary, although typically unacknowledged assumptions. Regression to the mean, the phenomenon of an unusual measurement typically followed by a more common one, can seriously bias observed changes in auditory function and clinical expectations. An approach that adjusts for this important effect is also described.

DESIGN

Distortion product otoacoustic emissions (DPOAEs) elicited at a single primary frequency, f2 of 3175 Hz, were collected from 32 healthy subjects at baseline and 19 to 29 days later. Ninety percent test-retest reference limits were computed from these data using each statistical approach. DPOAE shifts were also collected from a sample of 18 cisplatin patients tested after 120 to 200 mg of cisplatin. Reference limits established according to each of the statistical approaches in the healthy sample were used to identify clinically alarming DPOAE shifts in the cisplatin patient sample.

RESULTS

Reference limits established with any of the parametric methods were similar. The percentile-based approach gave the widest and least precisely estimated intervals. The highest sensitivity for detecting clinically alarming DPOAE shifts was based on a mixed model approach that adjusts for regression to the mean.

CONCLUSIONS

Parametric methods give similar serial monitoring criteria as long as certain critical assumptions are met by the data. The most flexible method for estimating test-retest limits is based on the linear mixed model. Clinical sensitivity may be further enhanced by adjusting for regression to the mean.

The alpha angle in cam-type femoroacetabular impingement

We report on gender-specific reference intervals of the alpha angle and its association with other qualitative cam-type findings in femoroacetabular impingement at the hip, according to a population-based cohort of 2038 19-year-olds, 1186 of which were women (58%). The alpha angle was measured on standardised frog-leg lateral and anteroposterior (AP) views using digital measurement software, and qualitative cam-type findings were assessed subjectively on both views by independent observers. In all, 2005 participants (837 men, 1168 women, mean age 18.6 years (17.2 to 20.1) were included in the analysis. For the frog-leg view, the mean alpha angle (right hip) was 47° (26 to 79) in men and 42° (29 to 76) in women, with 97.5 percentiles of 68° and 56°, respectively. For the AP view, the mean values were 62° (40 to 105) and 52° (36 to 103) for men and women, respectively, with 97.5 percentiles of 93° and 94°. Associations between higher alpha angles and all qualitative cam-type findings were seen for both genders on both views. The reference intervals presented for the alpha angle in this cross-sectional study are wide, especially for the AP view, with higher mean values for men than women on both views.

Cite this article: Bone Joint J 2014;96-B:449–54.

Population-based reference values for the 1-min sit-to-stand test

OBJECTIVES

To determine reference values for the 1-min sit-to-stand (STS) test in an adult population.

METHODS

Cross-sectional study nested within a nationwide health promotion campaign in Switzerland. Adults performed the STS test and completed questions on demographics and health behavior.

RESULTS

6,926 out of 7,753 (89.3 %) adults were able to complete the STS test. The median number of repetitions ranged from 50/min (25-75th percentile 41-57/min) in young men and 47/min (39-55/min) in young women aged 20-24 years to 30/min (25-37/min) in older men and 27/min (22-30/min) in older women aged 75-79 years.

CONCLUSIONS

The reference values support the interpretation of 1-min STS test performance and identification of subjects with decreased lower body muscular strength and endurance.

The rate of decline in small fibre function assessed using axon reflex-mediated neurogenic vasodilatation and the importance of age related centile values to improve the detection of clinical neuropathy

Background

The LDIflare technique (LDIflare) is a simple non-invasive test of small fibre function in dorsal foot skin involving skin heating and measuring the size of the resulting axon reflex-mediated vasodilator (flare) response using a laser Doppler imager (LDI). This study establishes age-related normative reference ranges for the test and determines the rate of decline in small fibre function per decade. Additionally, the potential value of using age related centiles rather than Receiver Operator Curves (ROC) was explored by comparison of the sensitivity and specificity of each analytic technique in identifying clinical neuropathy.

Methods

LDIflare areas were assessed in 94 healthy controls and 66 individuals with diabetes with (DN+, n = 31) and without clinical neuropathy (DN-, n = 35); neuropathy defined as a Neuropathy Disability Score ≥3. The age specific 5th centile values were used as the ‘cut-offs’ for the diagnosis of neuropathy from which sensitivity and specificity were calculated.

Results

There was a significant age dependant decrease in LDIflare size (r = −0.42, p<0.0001) with no significant gender differences. The LDIflare size reduced 0.56 cm² per decade which gives a percentage reduction of approximately 5.5% per decade. Using the normative 5th centiles as the cut-offs, the technique had a sensitivity of 77%, specificity of 90%, positive predictive value of 82% and negative predictive value of 87%.The ROC analysis gave a threshold of <3.66 cm² for the cut-off, resulting in a sensitivity of 75%, specificity of 85%, positive predictive value of 74% and negative predictive value of 86%.

Conclusions

There is an age dependent decrease in small fibre function in the foot of 5.5% per decade. Both analytic techniques demonstrate good sensitivity and specificity for detecting clinical neuropathy but the technique based on age centiles offers better diagnostic accuracy and is therefore proposed as the method of choice.

Modeling height for children born small for gestational age treated with growth hormone

The analysis of growth curves of children can be done on either the original scale or in standard deviation scores. The first approach is found in many statistical textbooks, while the second approach is common in endocrinology, for instance in the evaluation of the effect of growth hormone in children that are born small for gestational age that remain small later in childhood. We illustrate here that the second approach may involve more complex modeling and hence a worse model fit.

The de morton mobility index: normative data for a clinically useful mobility instrument

Determining mobility status is an important component of any health assessment for older adults. In order for a mobility measure to be relevant and meaningful, normative data are required for comparison to a healthy reference population. The DEMMI is the first mobility instrument to measure mobility across the spectrum from bed bound to functional levels of independent mobility. In this cross-sectional observational study, normative data were obtained for the DEMMI from a population of 183 healthy, community-dwelling adults age 60+ who resided in Vancouver, Canada and Melbourne, Australia. Older age categories had significantly lower DEMMI mobility mean scores (P < 0.05), as did individuals who walked with a mobility aid or lived in semi-independent living (assisted living or retirement village), whereas DEMMI scores did not differ by sex (P = 0.49) or reported falls history (P = 0.21). Normative data for the DEMMI mobility instrument provides vital reference scores to facilitate its use across the mobility spectrum in clinical, research, and policymaking settings.

Novel modeling of reference values of cardiovascular risk factors in children aged 7 to 20 years

BACKGROUND AND OBJECTIVE

Most of the cardiovascular risk factors strongly associated with obesity and overweight vary with age and gender. However, few reference values are available for healthy European children. Our objective was to establish pediatric reference ranges for waist circumference, systolic and diastolic blood pressures, fasting lipid levels (total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides), glucose, and insulin.

METHODS

A representative sample of 1976 healthy French individuals (1004 female participants and 972 male participants) aged 7 to 20 years was used to obtain age- and gender-specific normal ranges for each of the above-listed cardiovascular risk factors, based on the Royston and Wright method.

RESULTS

Mean waist circumference increased with age in both genders and was slightly higher in males than in females. Whereas systolic blood pressure increased gradually with age, with the increase being steeper in males than in females, no gender effect was found for diastolic blood pressure, which was therefore modeled after pooling males and females. Total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglyceride values varied little with age and gender. Glucose and insulin levels revealed pubertal peaks, which were sharper in females than in males, reflecting the normal insulin resistance during puberty.

CONCLUSIONS

These ranges can be used as references for European children to monitor cardiovascular risk factors and to plan interventions and education programs.

The Bowel Function Index for evaluating constipation in pain patients: definition of a reference range for a non-constipated population of pain patients

Opioid-induced constipation (OIC) is a severe, persisting side-effect of opioid therapy. The Bowel Function Index (BFI(a), numerical analogue scale 0 - 100), calculated as the mean of three variables (ease of defaecation, feeling of incomplete bowel evacuation, and personal judgement of constipation) was developed to evaluate bowel function in opioid-treated patients with pain. This clinician-administered tool allows easy measurement of OIC from the patient's perspective. The purpose of this investigation was to define a reference range reflecting BFI values in non-constipated chronic pain patients who were recruited into a cross-sectional survey and asked for their perceptions of constipation. The BFI scores were assessed and compared with those of patients with confirmed OIC obtained from two previously published trials. Results were analysed and a reference range of BFI values of 0 - 28.8, into which 95% of non-constipated chronic pain patients fell, was defined. This permits discrimination between chronic pain patients with, or without, constipation.

A two-part model for reference curve estimation subject to a limit of detection

Reference curves are commonly used to identify individuals with extreme values of clinically relevant variables or stages of progression which depend naturally on age or maturation. Estimation of reference curves can be complicated by a technical limit of detection (LOD) that censors the measurement from the left, as is the case in our study of reproductive hormone levels in boys around the time of the onset of puberty. We discuss issues with common approaches to the LOD problem in the context of our pubertal hormone study, and propose a two-part model that addresses these issues. One part of the proposed model specifies the probability of a measurement exceeding the LOD as a function of age. The other part of the model specifies the conditional distribution of a measurement given that it exceeds the LOD, again as a function of age. Information from the two parts can be combined to estimate the identifiable portion (i.e. above the LOD) of a reference curve and to calculate the relative standing of a given measurement above the LOD. Unlike some common approaches to LOD problems, the two-part model is free of untestable assumptions involving unobservable quantities, flexible for modeling the observable data, and easy to implement with existing software. The method is illustrated with hormone data from the Third National Health and Nutrition Examination Survey.

Consistency and reliability of self-reported lifetime number of heterosexual partners by gender and age in a cohort study

BACKGROUND

The reported number of sexual partners is a variable used extensively in sexual health research. However, the reliability and consistency of this measure, and the statistical assessment of these attributes, are not well understood.

METHODS

Using data at ages 21, 26, and 32 years from a New Zealand birth cohort, we compared responses on the lifetime number of heterosexual sex partners to assess reliability and consistency. Differences by gender and age were considered, and the effect of number of sexual partners. A variety of analytical methods were used to explore statistical challenges of these data including variance estimation, fractional polynomial transformations, and quantile regression.

RESULTS

We found some level of discrepancy between reports of the number of sexual partners when assessed at different times is common, driven by those reporting a high number of partners who were disproportionately men. Men reported a higher lifetime number of partners than women at each age, and there were statistically significant differences by gender in (a) consistency between reports at different ages, and (b) reliability of reports as measured by both the Intraclass Correlation Coefficient and the Kappa statistic.

CONCLUSIONS

When considering reliability, multiple statistical approaches are necessary or conclusions can be misleading. Variance components should be examined when considering the Intraclass Correlation Coefficient. When modelling, robust methods like fractional polynomials and quantile regression should be employed to accommodate nonlinearity. Sensitivity analyses excluding participants whose partner number is in the upper 5% to 25% are informative, as these were shown to have the highest discrepancies.

Thermoreception and nociception of the skin: a classic paper of Bessou and Perl and analyses of thermal sensitivity during a student laboratory exercise

About four decades ago, Perl and collaborators were the first ones who unambiguously identified specifically nociceptive neurons in the periphery. In their classic work, they recorded action potentials from single C-fibers of a cutaneous nerve in cats while applying carefully graded stimuli to the skin (Bessou P, Perl ER. Response of cutaneous sensory units with unmyelinated fibers to noxious stimuli. J Neurophysiol 32: 1025-1043, 1969). They discovered polymodal nociceptors, which responded to mechanical, thermal, and chemical stimuli in the noxious range, and differentiated them from low-threshold thermoreceptors. Their classic findings form the basis of the present method that undergraduate medical students experience during laboratory exercises of sensory physiology, namely, quantitative testing of the thermal detection and pain thresholds. This diagnostic method examines the function of thin afferent nerve fibers. We collected data from nearly 300 students that showed that 1) women are more sensitive to thermal detection and thermal pain at the thenar than men, 2) habituation shifts thermal pain thresholds during repetititve testing, 3) the cold pain threshold is rather variable and lower when tested after heat pain than in the reverse case (order effect), and 4) ratings of pain intensity on a visual analog scale are correlated with the threshold temperature for heat pain but not for cold pain. Median group results could be reproduced in a retest. Quantitative sensory testing of thermal thresholds is feasible and instructive in the setting of a laboratory exercise and is appreciated by the students as a relevant and interesting technique.

Lower incidence of procoagulant abnormalities during follow-up after creation of the Fontan circulation in children

OBJECTIVE

Children who undergo surgery for complex congenital cardiac disease are reported to be at increased thrombotic risk. Our aim was to evaluate long-term changes in the haemostatic system after surgery, to compare markers of activated coagulation in children having surgery with those in a healthy control population, and to relate them to adverse clinical outcome.

PATIENTS AND METHODS

We studied, prior to surgery, the coagulation profiles of a cohort of 28 children admitted for a modified Fontan operation, studying them again after a period of mean follow-up of 9.6 years. Median age at the time of final surgery was 18.5 months, with a range from 12 to 76 months. We compared generation of thrombin, and levels of the activated protein C-protein C inhibitor complex to controls at follow-up. Thrombophilia and clinical outcome were evaluated.

RESULTS

At long-term follow-up, a lower incidence of procoagulant abnormalities was observed compared to that before surgery. Of 27 patients, 3 (11%), but none of 45 controls, had levels of activated protein C-protein C inhibitor complex above the reference range. There were no significant differences in generation of thrombin between patients and controls. No thrombotic events were recorded, and the patients were generally in good clinical condition.

CONCLUSIONS

Overall, haemostasis appeared to be in balance, and less prothrombotic, after surgery. A subset of the cohort did show indications of activated coagulation. The current therapeutic approach seems to be sufficient to protect the majority of patient. New tests of global coagulation, nonetheless, may be helpful in improving identification of individuals at increased thrombotic risk.

Breed-associated variability in serum biochemical analytes in four large-breed dogs

BACKGROUND

Genetic background can influence the expected values of hematologic and serum biochemical analytes in domestic animal species.

OBJECTIVE

The purpose of this study was to determine if there are breed-related differences in serum biochemical variables in healthy purebred dogs of 4 breeds and to develop appropriate reference intervals.

METHODS

Alaskan Malamutes (n=59), Siberian Huskies (n=78), Golden Retrievers (n=90), and English Setters (n=77) were included in the study. The dogs had a median age of 42 months (range 10-112 months) and each breed included a mix of intact and neutered dogs of both sexes. Serum biochemical profiles (Olympus AU400e) were performed along with physical examinations, CBCs, and urinalyses to ensure dogs were clinically healthy. Differences in the values of biochemical analytes were assessed nonparametrically and reference intervals for all breeds combined were calculated as the central 95% percentile.

RESULTS

Significant differences were observed between breeds for all serum biochemical analytes except alkaline phosphatase, glucose, and chloride. The analyte ranges had a large degree of overlap between the different breeds.

CONCLUSIONS

Although many statistically significant breed-related differences in serum biochemical values were observed, the differences were small and unlikely to have clinical relevance or impact medical decision making.

Range Charts for Agreement in Measurement Comparison Studies, With Application to Replicate Mass Spectrometry Experiments

It is important to investigate the reproducibility of raw mass spectrometry (MS) features of abundance, such as spectral count, peptide number and ion intensity values, when conducting replicate mass spectrometry measurements. Reproducibility can be inferred from these replicate data either formally with analyses of variance techniques or informally with graphical procedures, particularly, Bland-Altman plots on paired runs. In this note, we suggest range plots to provide a suitable generalization of Bland-Altman plots to experiments with more than two replicate runs. We describe range charts and their interpretation, and illustrate their use with data from a recent proteomic study relating to label-free analysis.

Reference curves for the Gross Motor Function Measure: percentiles for clinical description and tracking over time among children with cerebral palsy

BACKGROUND AND PURPOSE

Physical therapists frequently use the 66-item Gross Motor Function Measure (GMFM-66) with the Gross Motor Function Classification System (GMFCS) to examine gross motor function in children with cerebral palsy (CP). Until now, reference percentiles for this measure were not available. The aim of this study was to improve the clinical utility of this gross motor measure by developing cross-sectional reference percentiles for the GMFM-66 within levels of the GMFCS.

SUBJECTS AND METHODS

A total of 1,940 motor measurements from 650 children with CP were used to develop percentiles. These observations were taken from a subsample, stratified by age and GMFCS, of those in a longitudinal cohort study reported in 2002. A standard LMS (skewness-median-coefficient of variation) method was used to develop cross-sectional reference percentiles.

RESULTS

Reference curves were created for the GMFM-66 by age and GMFCS level, plotted at the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles. The variability of change in children's percentiles over a 1-year interval also was investigated.

DISCUSSION AND CONCLUSION

The reference percentiles extend the clinical utility of the GMFM-66 and GMFCS by providing for appropriate normative interpretation of GMFM-66 scores within GMFCS levels. When interpreting change in percentiles over time, therapists must carefully consider the large variability in change that is typical among children with CP. The use of percentiles should be supplemented by interpretation of the raw scores to understand change in function as well as relative standing.

Aflatoxin exposure in utero causes growth faltering in Gambian infants

BACKGROUND

Growth faltering in West African children has previously been associated with dietary exposure to aflatoxins, particularly upon weaning. However, in animal studies in utero exposure to low levels of aflatoxin also results in growth faltering.

OBJECTIVE

This study investigated the effect of in utero aflatoxin exposure on infant growth in the first year of life in The Gambia.

METHODS

Height and weight were measured for 138 infants at birth and at regular monthly intervals for one year. Aflatoxin-albumin (AF-alb) adduct level was measured in maternal blood during pregnancy, in cord blood and in infants at age 16 weeks.

RESULTS

The geometric mean AF-alb levels were 40.4 pg/mg (range 4.8-260.8 pg/mg), 10.1 pg/mg (range 5.0-189.6 pg/mg) and 8.7 pg/mg (range 5.0-30.2 pg/mg) in maternal, cord and infant blood, respectively. AF-alb in maternal blood was a strong predictor of both weight (P = 0.012) and height (P = 0.044) gain, with lower gain in those with higher exposure. A reduction of maternal AF-alb from 110 pg/mg to 10 pg/mg would lead to a 0.8 kg increase in weight and 2 cm increase in height within the first year of life.

CONCLUSIONS

This study shows a strong effect of maternal aflatoxin exposure during pregnancy on growth in the first year of life and thus extends earlier observations of an association between aflatoxin exposure during infancy and growth faltering. The findings imply value in targeting intervention strategies at early life exposures.