URINE-FREE CORTISOL EXCRETION - EVIDENCE OF SEX-DEPENDENCE

Measurement of urine-free (unconjugated) cortisol (UFC) excretion is w idely used in the investigation of hypercortisolaemia. We have measure d 24 h UFC excretion in normal healthy individuals using a radioimmuno assay (RIA) method claimed to be suitable for unextracted urine. Signi ficantly higher rates of excretion were found in a group of 15 men com pared with a group of 18 women, with median values of 230 (range 145-3 34) and 149 (range 67-315)nmo1/24h, respectively (P < 0.005). This met hod was used to reanalyse the urine samples after extraction with dich loromethane. Although values were significantly lower than those found with unextracted urine (P< 0.001), the male:female difference remaine d with median values of 140 (range 96-295) and 112 (range 29-196)nmo1/ 24h, respectively (P < 0.02). Rates of UFC excretion were measured on the same dichloromethane-extracted urine samples using a second, diffe rent RIA, which again demonstrated the male:female difference with med ian values of 151 (range 116-302) and 109 (range 36-205) nmo1/24 h, re spectively (P < 0.001). There was no significant difference between th ese values and those obtained with extracted urine in the first assay. The higher rates of UFC excretion in men compared to women does not a ppear to be due to the presence of interfering compounds since the dif ference is also present using extracted urine samples and with two met hods using different antibodies. These results should be borne in mind by laboratories when interpreting UFC results.