The measurement of plasma Δ 4-androstenedione by competitive protein binding

A sensitive competitive protein binding (CPB) method capable of measuring Δ 4-androstenedione (Δ 4) in 3 ml of plasma is presented. This method utilizes third trimester pregnancy plasma as a source of testosterone binding globulin and the conversion of Δ 4 to testosterone (T) by potassium borohydride. Dextran coated charcoal is used to separate the free steroid from the bound. Analysis of twenty standard curves in the range of 0–1 ng T provided coefficients of variation from 5.9% at 0.2 ng T to 7.9% at 1.0 ng T. The mean recovery of tritiated Δ 4 added to plasma as a tracer was 31.6%. Normal values for adult males and females as determined by this CPB method fall within the range of published values as determined by double isotope derivative assays (DIA) and gas liquid chromatography (GLC). Compared to the DIA and GLC methods, the blank of this method is higher and the measurement of replicate samples is slightly less precise.