Measurement of Progesterone in Bovine Plasma and Preserved Whole Blood Samples by a Direct Radioimmunoassay

Abstract

A close correlation ( r = 0·89) has been established between results of direct and extraction assays of progesterone in bovine plasma samples. The direct assay yielded somewhat higher results than the conventional extraction method (means ± SEM: direct 3·5 ± 0·6 ng/ml, extraction 2·5 ± 0·5 ng/ml). Storage of whole blood at room temperature or at 4°C for 12 to 24 h before separation of plasma results in the reduction of progesterone levels measured in plasma by between 20 and 70%. Although addition of a potassium dichromate and mercuric chloride preservative tablet haemolysed the samples, progesterone could be assayed successfully in the haemolysed blood. Results of assays on haemolysed blood were higher than those obtained by direct assay of the corresponding plasma (means ± SEM : plasma 4·4 ± 0·4 ng/ml, blood 5·3 ± 0·4 ng/ml) but results from the two sample types were closely correlated ( r = 0·93). It is suggested that measurement of progesterone in bovine haemolysed blood could be used as the basis for a pregnancy test or in other applications where it is not essential to measure absolute levels.