title: Interlaboratory evaluation of four RIA kits for determination of plasma cortisol, with special reference to accuracy: influence of matrix in calibration standards.
abstract: We used four RIA kits for determination of plasma cortisol to assay 12 plasma samples in four laboratories, and compared the results with those obtained with a highly accurate method based on isotope dilution/mass spectrometry. All kits (Farmos, NEN, Sorin, and Clinical Assays) showed 10-50% deviation from the comparison method in the normal range (200-700 nmol/L). The inter- and intralaboratory imprecision (CV) ranged between 8-27% and 5-11%, respectively. Possible explanations for this low accuracy are discussed. Retention of an intact biological matrix in the calibration standards seems to be one prerequisite for accuracy.
mesh_terms: D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D011786:Quality Control; D011863:Radioimmunoassay / Q000379:methods; D011933:Reagent Kits, Diagnostic
chemical_list: D011933:Reagent Kits, Diagnostic; D006854:Hydrocortisone