Clinical guidance recommends titrating the dose of metyrapone against serum cortisol concentrations. These serum samples are usually measured by immunoassays; however it has been well documented that there are interferences in these assays in patients with altered steroid metabolism due to a pathological process or drug treatment. The increasing availability of mass spectrometry (MS) assays for steroid hormones may circumvent this issue and assays that measure multiple steroids may also be used to elucidate the nature of the interferences seen.
Sera from two patients on metyrapone therapy were analysed using a liquid chromatography tandem MS assay for cortisol, 11 deoxycortisol, 21 deoxycortisol, 17 hydroxyprogesterone and androstenedione to identify which steroids may be elevated in these patients causing an interference. We also spiked a series of steroids into serum to identify, which may give rise to an apparent increase in cortisol measured by immunoassay. The steroids used were 11 deoxycortisol, 21 deoxycortisol, androstenedione, 17 hydroxyprogesterone, 21 hydroxyprogesterone, progesterone and testosterone. The sera were analysed by a Roche electrochemiluminescent immunoassay.
The steroid panel results for the sera show a marked increase in 11 deoxycortisol but not any of the other steroids, confirming other findings. Spiking studies show that 11 deoxycortisol does not cause enough of an increase in immunoassay cortisol to account for the interference seen in patients receiving metyrapone. The only steroid shown to cause a significant interference in the immunoassay was 21 deoxycortisol, but MS analysis of the samples has not shown this to be increased in the serum.
Although none of the steroids tested could be identified as the cause of the interference and we have excluded these common steroid precursors and metabolites as suspects. Clinicians should be aware of the interferences when monitoring response to treatment and the measurement of serum cortisol by MS should be sought.