Between-Method Variation in Human Chorionic Gonadotropin Test Results

Background: Results on sera and calibrators vary 1.4- to 2.3-fold among commercial human chorionic gonadotro-pin (hCG) assays. The relative contributions of calibra-tors, standards, hCG charge isoforms, and major struc-tural variants to this variation have not been quantified. Methods: Purified hCG was separated by isoelectric focusing into four fractions with pI ranges of 3–4, 4–5, 5–6, and 6–7. These four fractions together with pure hCG, hyperglycosylated hCG, hCG -subunit (hCGb), nicked hCG, and hCGb core fragment (hCGbcf) were tested in nine commonly used commercial serum assays for hCG. The compositions of pure hCG preparations, standards, and commercial hCG preparations were de-termined by immunoassay. Results: The three pure hCG preparations and the fou