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Validation of 5 routine assays for serum free testosterone with a candidate reference measurement procedure based on ultrafiltration and isotope dilution–gas chromatography–mass spectrometry

2005; Elsevier BV; Volume: 38; Issue: 3 Linguagem: Inglês

10.1016/j.clinbiochem.2004.12.001

1873-2933

Katleen Van Uytfanghe, Dietmar Stöckl, Jean‐Marc Kaufman, Tom Fiers, A. De Leenheer, Linda M. Thienpont,

Pharmacological Effects and Assays

The analytical validity of free testosterone (FTe) analog immunoassays is subject to much controversy. We revisited the validation of 4 analog assays and 1 FTe calculation procedure with a metrologically traceable reference measurement procedure (RMP) based on ultrafiltration and isotope dilution–mass spectrometry for direct measurement of Te in the ultrafiltrate. To this end, we performed split-sample measurements of 40 male sera. Deming regression showed that 3 of the immunoassays had moderate to good correlation (0.8474 ≤ r ≤ 0.9241) with the RMP; however, the slope was markedly below 1. The FTe calculation procedure was in good agreement with this result. The Sy/x values for all assays were higher than the combined imprecision values, which indicate their susceptibility to matrix-related effects. The study demonstrated substantial differences in analytical quality of FTe assays; however, the results suggested that after extending the validation with a larger variety of samples, recalibration of some analog assays might be worth further investigation.