Dynamic biological changes in metabolic disease biomarkers in childhood and adolescence: A CALIPER study of healthy community children.

BACKGROUND: Understanding age- and sex-specific biological changes in metabolic disease biomarkers is essential for their appropriate utilization in management of children with inborn errors of metabolism (IEM). The CALIPER program aimed to establish pediatric reference values in healthy community children for common metabolic biomarkers and determine the effects of key covariates including age and sex across the pediatric age. METHODS: A cohort of 500 healthy children and adolescents from birth to 19years were initially recruited to establish pediatric reference intervals according to the CLSI C28-A3 guidelines. Serum samples were used to measure 37 amino acids by ultra-performance liquid chromatography, 32 acylcarnitines, as well as free and total carnitine by tandem mass spectrometry, and ß-hydroxybutyrate and free fatty acids using the Vitros 5.1 chemistry analyzer. P ediatric reference intervals were calculated using non-parametric statistics and partitioned based on age- and sex-distributions. RESULTS: Approximately 80% of all analytes required 2 to 4 age-dependent partitions, with over 50% of amino acids and over 70% of acylcarnitines exhibiting significant physiological changes during the neonatal period. Also, 21% of all analytes required partitioning during puberty and adolescence, half of which produced sex-specific distributions. CONCLUSIONS: A comprehensive reference interval database for metabolic disease biomarkers established in this study will improve detection of IEMs by providing appropriate age- and sex-related information in the pediatric population. It will also aid newborn screening programs and guide the management of patients with known metabolic diseases, especially pubertal and adolescent boys and girls that display sex-specific concentrations.

Evaluation of a next generation direct whole blood enzymatic assay for hemoglobin A1c on the ARCHITECT c8000 chemistry system.

BACKGROUND: The utility of HbA1c for the diagnosis of type 2 diabetes requires an accurate, precise and robust test measurement system. Currently, immunoassay and HPLC are the most popular methods for HbA1c quantification, noting however the limitations associated with some platforms, such as imprecision or interference from common hemoglobin variants. Abbott Diagnostics has introduced a fully automated direct enzymatic method for the quantification of HbA1c from whole blood on the ARCHITECT chemistry system. METHODS: Here we completed a method evaluation of the ARCHITECT HbA1c enzymatic assay for imprecision, accuracy, method comparison, interference from hemoglobin variants and specimen stability. This was completed at three independent clinical laboratories in North America and Europe. RESULTS: The total imprecision ranged from 0.5% to 2.2% CV with low and high level control materials. Around the diagnostic cut-off of 48 mmol/mol, the total imprecision was 0.6% CV. Mean bias using reference samples from IFCC and CAP ranged from -1.1 to 1.0 mmol/mol. The enzymatic assay also showed excellent agreement with HPLC methods, with slopes of 1.01 and correlation coefficients ranging from 0.984 to 0.996 compared to Menarini Adams HA-8160, Bio-Rad Variant II and Variant II Turbo instruments. Finally, no significant effect was observed for erythrocyte sedimentation or interference from common hemoglobin variants in patient samples containing heterozygous HbS, HbC, HbD, HbE, and up to 10% HbF. CONCLUSIONS: The ARCHITECT enzymatic assay for HbA1c is a robust and fully automated method that meets the performance requirements to support the diagnosis of type 2 diabetes.

Pediatric reference value distributions for vitamins A and E in the CALIPER cohort and establishment of age-stratified reference intervals.

OBJECTIVES: Vitamin A (retinol) and vitamin E (α-tocopherol) are fat soluble micronutrients most commonly measured in the pediatric population to monitor deficiencies due to malabsorption secondary to gastrointestinal (GI) disorders. One of the major challenges of vitamin A and E testing is the lack of reliable pediatric reference intervals which limits accurate interpretation of results. Here we report new pediatric reference intervals (RI) for both vitamins as part of the Canadian Laboratory Initiative for Pediatric Reference Intervals (CALIPER). DESIGN AND METHODS: A total of 342 blood samples were collected from healthy children 1 day to 19 years of age recruited from the community. Retinol and α-tocopherol were extracted from serum using hexane before concentrations were measured with high-performance liquid chromatography (HPLC). Age and sex-specific RI were calculated with guidance from CLSI C28-A2. Non-parametric and robust methods were used to calculate the 95th percentile ranges of the reference intervals along with the 90% confidence intervals. RESULTS: Vitamin A demonstrated increasing levels with age necessitating four distinct age stratifications. Vitamin E levels peaked within the first year of life requiring only 2 age partitions. Ratios of vitamin E to cholesterol and triglyceride were also calculated, and correlated well to vitamin E levels. Sex-specific differences were not observed. CONCLUSIONS: This study establishes pediatric RI for vitamins A and E in a healthy population of children from neonates to early adulthood. These values will be beneficial in assessing accurate vitamin status when monitoring children with GI disorders or malnutrition.