Immunoglobulin G (IgG) and IgG subclass reference intervals in children, using Optilite® reagents.

BACKGROUND: Immunoglobulin G (IgG) and IgG subclass assays are indicated in patients with suspected primary immunodeficiency (PID). Commercially available assays for IgG subclass determination are calibrated against various preparations, and so specific reference values are required for each of them. Using Optilite® reagents from The Binding Site Group Ltd., we sought to determine the pediatric IgG and IgG subclass reference intervals with respect to the ERM-DA470k certified reference material. METHODS: Levels of IgG and IgG subclasses were analyzed in serum samples collected from a large cohort of PID-free children and adolescents. Reference intervals were calculated for previously published age groups (6-12 months, 12-18 months, 18 months-2 years, 2-3 years, 3-4 years, 4-6 years, 6-9 years, 9-12 years and 12-18 years), according to the Clinical and Laboratory Standards Institute's C28-A3c protocol. RESULTS: A total of 456 serum samples were analyzed. The correlation between the total IgG and the sum of the IgG subclasses was good (r2=0.96). No statistically significant gender-specific differences were observed. Our results for the changes over time in IgG and IgG subclass levels are consistent with previous reports. The differences between our lower/upper reference limits and those in the literature are probably due to variations in calibration. CONCLUSIONS: Our present results provide a reliable basis for the diagnosis of PIDs in childhood and for the accreditation of laboratories using Optilite® immunoturbidimetric reagents for IgG subclass measurement. Laboratory scientists and clinicians should be aware of the need for manufacturer-specific IgG subclass reference intervals.

First two-reagent vitamin D assay for general clinical chemistry.

BACKGROUND: Vitamin D is a lipid-soluble molecule that plays key physiological roles in the metabolism of calcium, phosphate and magnesium. Recent studies show that deficiency in vitamin D is linked to cardiovascular diseases, autoimmune diseases and cancer. As a result, regular monitoring of 25-OH vitamin D (the main circulating form of vitamin D) is becoming essential. Current 25-OH vitamin D testing methodologies are cumbersome (too many reagents, long incubation times, phase separation) and are not compatible with general clinical chemistry platforms. Here, we report on a novel method to detect 25-OH vitamin D that is fast (results in 10 min or less), simple (two reagents) and compatible with virtually all general clinical chemistry analyzers. METHODS: An immunoturbidimetric assay for 25-OH vitamin D (the Diazyme EZ Vitamin D Assay) has been developed using nanoparticles and vitamin D-specific antibodies. The performance of the assay kit, which consists of two reagents and five calibrators, was tested on the Beckman AU680 analyzer (AU680). RESULTS: The new assay was precise, sensitive (LOD = 7.2 nmol/L), linear (up to 390.1 nmol/L) and correlated strongly (R2 > 0.95) with major commercial 25-OH vitamin D assays. Additionally, the assay was found to be the fastest to date, with the first results obtained within 10 min. Throughput on the AU680 was estimated at over 300 tests per hour. CONCLUSIONS: The newly developed 25-OH vitamin D assay is fast, precise and accurate. It can be run on most general chemistry analyzers. This assay aims at providing vitamin D-testing capabilities to all clinical chemistry laboratories.