Which urinary metabolite of cortisol is detected using the Porter-Silber Method with 2,4-DNPH and yields a positive yellow reaction?

• A. 17-hydroxycorticosteroids
• B. 17-ketosteroids
• C. DHEA
• D. Cortisol

Answer: (A)

Porter-Silber uses 2,4-dinitrophenylhydrazine to detect carbonyl-containing steroids in urine. After hydrolysis, the cortisol metabolites that retain a reactive carbonyl structure react with the reagent to form a hydrazone, producing a yellow color. The commonly measured urinary metabolites of cortisol are the 17-hydroxycorticosteroids, so this yellow reaction indicates their presence. Other steroids either aren’t the primary urinary products detected by this method or are not measured directly in this assay (for example, 17-ketosteroids, DHEA, or the parent cortisol), which is why 17-hydroxycorticosteroids is the best match.