Measurement of human urinary prolactin as a noninvasive study tool

We used a time-resolved solid-phase fluoroimmunoassay with a sensitivity of 25 ng/L on 40-fold-concentrated urines to measure urine prolactin (PRL) excretion. The nature of the immunoreactive material was verified to be PRL by: (a) column chromatography showing a monomeric 23-kDa peak; (b) similarity between fluoroimmunoassay and bioassay (Nb2 lymphoma cell) results; and (c) Western blot identification. In 20 normal subjects [serum PRL 6.8 (3.8-14.0) micrograms/L, median (and range)], urine PRL excretion was 0.15 (0.07-0.23) ng/h and 0.24 (0.15-0.54) micrograms/mol of creatinine. Urine values in seven hyperprolactinemic patients were all greater than the upper limit of normal. The correlation between urinary excretion rate and serum values was highly significant (r = 0.979; P < 0.001). These results indicate that a monomeric, immunologically reactive, biologically active form of PRL can be measured in urine at concentrations approximately 0.0005 that in serum. This urine PRL method may provide a practical tool for the repetitive, noninvasive study of PRL dynamics in field studies and in patients with reproductive disorders.