Dried Blood Spot Reference Intervals for Steroids and Amino Acids in a Neonatal Cohort of the National Children's Study.

BACKGROUND: Reference intervals from children are limited by access to healthy children and their limited blood volumes. In this study we set out to fill gaps in pediatric reference intervals for amino acids and steroid hormones using dried blood spots (DBS) from a cohort of the National Children's Study. METHODS: Deidentified DBS annotated with age, birthweight, sex, and geographic location were obtained from 310 newborns aged 0-4 days and analyzed for 25 amino acids and 4 steroid hormones using LC-MS/MS. Nonparametric statistical approaches were used to generate the 2.5th-97.5th percentile distributions for newborns. Paired plasma/DBS specimens were used to mathematically transform DBS reference intervals to corresponding plasma intervals. RESULTS: 10 of 25 DBS amino acid distributions were dependent on sex. There was little correlation with age, birthweight, or geographic location over the first 4 days of life. In most cases, transformation of DBS distributions to plasma distributions faithfully reflected independent studies of newborn plasma amino acid distributions. In general newborn steroid distributions were negatively correlated with age and birthweight over the first 4 days of life. Data distributions for the 4 steroids were not found related to geographic location, but testosterone concentrations displayed sex dependence. Transformation of DBS distributions to plasma intervals did not faithfully replicate other neonate steroid reference intervals determined directly with plasma. CONCLUSIONS: These data demonstrate the feasibility and utility of deriving newborn reference intervals from large numbers of archived DBS samples such as those obtained from the National Children's Study biobank.

Reference interval estimation: Methodological comparison using extensive simulations and empirical data.

OBJECTIVE: To statistically compare and evaluate commonly used methods of estimating reference intervals and to determine which method is best based on characteristics of the distribution of various data sets. DESIGN AND METHODS: Three approaches for estimating reference intervals, i.e. parametric, non-parametric, and robust, were compared with simulated Gaussian and non-Gaussian data. The hierarchy of the performances of each method was examined based on bias and measures of precision. The findings of the simulation study were illustrated through real data sets. RESULTS: In all Gaussian scenarios, the parametric approach provided the least biased and most precise estimates. In non-Gaussian scenarios, no single method provided the least biased and most precise estimates for both limits of a reference interval across all sample sizes, although the non-parametric approach performed the best for most scenarios. The hierarchy of the performances of the three methods was only impacted by sample size and skewness. Differences between reference interval estimates established by the three methods were inflated by variability. CONCLUSIONS: Whenever possible, laboratories should attempt to transform data to a Gaussian distribution and use the parametric approach to obtain the most optimal reference intervals. When this is not possible, laboratories should consider sample size and skewness as factors in their choice of reference interval estimation method. The consequences of false positives or false negatives may also serve as factors in this decision.

A systematic review of statistical methods used in constructing pediatric reference intervals.

OBJECTIVES: This study aims to investigate current medical literature with focus on statistical methods used to construct pediatric reference intervals and identify potential gaps within the process of reference interval estimation. DESIGN AND METHODS: A systematic review of methods was performed. Extensive search criteria were developed and search was conducted on Embase, Medline, and PubMed databases to identify relevant articles. The articles were further screened using predefined inclusion and exclusion criteria. The selected articles were then included in our final systematic review. RESULTS: Our review reveals that there are gaps within current methodology and reporting of pediatric reference intervals. Not all publications followed the Clinical and Laboratory Standards Institute (CLSI) guidelines, and there is a large variation in the methods used. Discrepancies particularly arose when reference intervals were calculated for partitions with small sample sizes. In addition, the dynamic nature of pediatric data was not mostly captured when certain partitioning techniques were used. CONCLUSIONS: There are areas within the pediatric reference interval development process that need attention. Partitioning methods particularly need to be explored with the goals of reducing subjectivity and enabling researchers to capture the best representative partitions possible. Moreover, the complicated nature of pediatric data often limits the sample size available for each partition and appropriate methods need to be considered in such cases. Researchers are also strongly encouraged to accompany their reference limits with confidence intervals to show sampling variability and demonstrate precision of their limits. These issues exemplify the need for a pediatric specific guideline that outlines a standardized way of establishing reference intervals.

Improving serological test ordering patterns for the diagnosis of celiac disease through clinical laboratory audit of practice.

BACKGROUND: Clinical Practice Guidelines (CPG) from both adult medicine and pediatrics recommend tTG to screen for celiac disease (CD). DESIGN AND METHODS: Serological test orders for celiac disease were evaluated against the guidelines. Ordering physicians were categorized as gastroenterologists, immunologists, pediatricians, other hospital physicians and non-hospital physicians. Interventions based on initial audit were implemented, including interacting with physicians, revising test menu and changing test ordering policy. After implementation of interventions, test orders were re-evaluated. RESULTS: After corrective interventions celiac panel (CP) orders were decreased from 48.4% to 3.6% in children, and from 72.3% to 28.1% in adults. Physicians ordered tTG alone for more than 90% of children. In adults the ordering of tTG alone was significantly increased from 7.2% to 61.3% (from 8.9% to 63.9% for gastroenterologists and from 8.1% to 44.4% for other physicians (p<0.05)). CONCLUSIONS: The audit reduced the CPG-practice gap that existed in the screening of CD.