Performance characteristics of the IMMULITE 2000 insulin-like growth factor binding protein-3 assay

BACKGROUND: Insulin-like growth factor binding protein-3 (IGFBP-3) is the chief binding protein for insulin-like growth factors 1 and 2 (IGF-1 and IGF-2). Serum concentrations of IGFBP-3 are regulated by growth hormone (GH) and IGF-1 levels. Serum IGFBP-3 measurements are useful for diagnostic evaluations of short stature in children and acromegaly. METHODS: A IGFBP-3 assay for the IMMULITE 2000 analyzer was evaluated for limit of detection, linearity, intra- and interassay imprecision, comparison to another commercially available assay, interference studies, and an adult reference interval. RESULTS: The limit of detection was 0.006 mg/l. The assay was linear from 0.01 to 15.1 mg/l. The total interassay imprecision was <6% for IGFBP-3 concentrations of 1.1 and 4.4 mg/l. Comparison with a Nichols RIA method showed comparable results. Deming regression analysis gave a slope of 1.02+/-0.02, an intercept of 0.24+/-0.07, and a Sy/x of 0.33 (r=0.98) over the range tested (0.4 to 10.3 mg/l). Interference was <10% for all levels of bilirubin, triglyceride, and hemoglobin tested. The nonparametric reference interval for adults 26 to 61 years was 2.9 to 6.5 ng/ml. CONCLUSIONS: The IMMULITE 2000 IGFBP-3 assay shows acceptable performance and is suitable for routine clinical use.