Measurementof UrinaryFree 20a-Dihydrocortisol in BiochemicalDiagnosis of ChronicHypercorticoidism

Using liquid chromatography, we estimated the urinary excretion of20a-dihydrocortisol (20-DH)and urinary freecortisol (UFC)innormalsubjects and in40 patients withCushing’s syndrome of different etiologies. The median normal excretion rate (nmol/24 h) was 174 for 20-DH and 68 for UFC, the 20-DH/UFC ratio thus being 2.55. For patients with Cushing’s syndrome, the excretion rate was 1798 for 20-DH and 298 for UFC, the ratio 6.03. We evaluated the effect of acute stimulation of adrenal secretion on 20-DH and UFC by administering corticotropin to six normalsubjects. Aftersuch stimulation, the excretion rate was 566 for20-DH and 1238 for UFC (ratio 0.45). Whereas 20-DH excretion rate exceeded the normalrange in all patients, six patients had normal or even below-normal values for UFC excretion. Evidently, measurement of urinary 20-DH is a better testforchronic hypercorticoidismthan is measurementof urinaryUFC, and chronic hypercorticoidism can be differentiated from the acutestateby the 20-DH/UFC ratio.