ASSAY OF PLASMA TESTOSTERONE DURING THE FIRST 6 MONTHS OF LIFE - IMPORTANCE OF CHROMATOGRAPHIC PURIFICATION OF STEROIDS

Determination of the plasma concentration of testosterone (T) is impor tant in evaluating infants born with ambiguous genitalia and micropeni s, and several commercially available kits provide a direct assay of T in unextracted plasma, Using plasma samples obtained from 36 subjects <6 months old, we compared the concentration of plasma T measured by RIA after extraction and purification by column chromatography with th e T concentration measured in a direct assay. When aliquots of samples were purified before RIA, the concentration of T was markedly lower t han in the direct assay. In the first 3 weeks postpartum, results of t he direct assay were 3.8-fold greater than those obtained after purifi cation. This difference decreased over time, and by age 2 months there was fairly good agreement between the two methods, These data indicat e that some direct assays of plasma T are inappropriate during the fir st 2 months postpartum.