A comparison of progesterone assays for determination of peripheral pregnane concentrations in the late pregnant mare.

The research article centers around comparing and evaluating four different immunoassays to determine progesterone concentrations in late-pregnant mares. The study aims to better understand the assays’ cross-reactivity with different pregnanes in the blood samples of the mare during the latter part of gestation.

Objectives

The study aimed to:

• Compare four immunoassays with LC-MS/MS (liquid chromatography combined with mass spectrometry) for determining pregnane concentrations
• Evaluate the degree of cross-reaction between these immunoassays and various pregnanes namely pregnenolone (P5), progesterone (P4), 5α-dihydroprogesterone (DHP), allopregnanolone, and altrenogest.

Methodology

The researchers collected blood samples from four healthy mares in late gestation. These samples were then evaluated using immunoassays and the LC-MS/MS method. Further, varying degrees of cross-reactivity of the immunoassays with other pregnanes were assessed.

Findings

The study found that:

• There were significant differences in the progesterone concentrations ascertained by each of the tested immunoassays.
• The results were closely correlated despite the differences in measured progesterone concentrations.
• The concentrations measured by immunoassay were linearly associated with concentrations of P5, P4, DHP, and allopregnanolone determined by LC-MS/MS
• No detectable cross-reaction of altrenogest was found in any of the immunoassay tests, but varying degrees of cross-reactivity were observed with the other pregnanes under study.

Conclusion

These findings suggest that the type of assay used and its cross-reactivity with different pregnanes in the blood can influence the progesterone concentrations measured during the late stages of gestation. The study underscores the need for careful consideration and interpretation of progesterone assay results in late-pregnant mares, especially regarding potential cross-reactivity with other pregnanes in the blood. However, altrenogest, a synthetic progestin, did not affect the results of any immunoassay in the study.