Testosterone/Dihydrotestosterone Kit Method for Diagnostic Use

To the Editor: During early fetal life of males, con-version of testosterone (T) to 5a-dihy-drotestosterone (DHT) via the action of 5a-reductase in the external genital tissues is essential for complete sexual differentiation of male external genita-lia. Measurement of low concentra-tions of DHT in serum of affected pre-pubertal males confirms the type of sexual disorder (1,2). Although commercial methodologies have been available for T determina-tions for many years, to our knowledge no similar diagnostic methods have been available for measuring DHT. Recently, Amersham (Oakville, Ontar-io) marketed a combination kit (cat. no. TRK.600) for measuring testosterone! dihydrotestosterone by radioim-munoassay, for research use only, and we have compared the performance of this kit with that of our own in-house T method in a clinical setting. In our in-house method, we extract serum samples (0.5 mL male, 1.0 mL female) twice with 3-mL portions of diethyl ether and evaporate the extract in plastic tubes under air. The residue is reconstituted in 1 mL of pH 7.4 phosphate buffer and radioimmunoas-sayed. The testosterone antiserum is from Diagnostics Biochem Inc. (London, On-tario), the testosterone standard fro