Analyses for progesterone in serum by gas chromatography/mass spectrometry: target data for external quality...

We describe a procedure for measuring progesterone in plasma and serum by isotope dilution and mass spectrometry. Extraction with use of a microcellulose-coupled antiserum is followed by conversion to the 3-enol heptafluorobutyrate and analysis by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring, at a resolution of 5000. Interassay CVs were 1.5 to 5.4% for the concentration range 13 to 43 nmol/L. Analyses of various serum volumes showed excellent linearity. Accurate determination of progesterone added to serum was demonstrated. Plasma and serum pools were analyzed to provide target data for use in the U.K. national external quality-assessment scheme for progesterone assays. Direct, non-extraction radioimmunoassays and those incorporating solvent extraction both showed a positive bias with respect to data obtained by the present procedure, but the bias was more marked with the direct assays.