Immunoreactive inhibin concentration in blood tested under variable sampling conditions

The stability of immunoreactive (i.r.) inhibin in blood samples drawn and handled under different conditions and at different time intervals were studied. Ten serum and plasma samples drawn in 1994 from healthy volunteers were compared to samples collected in 1986 from 10 healthy women admitted for laparoscopic sterilization and analysed 6 years later. All samples were drawn on the twelfth day of the menstrual cycle and handled under identical clinical conditions (22 degrees C). The concentrations in the 1986 samples were similar to the Se-i.r. inhibin levels from 1994. Different clotting temperatures, repetitive freezing and thawing or hemolysis had no effects on the i.r. inhibin values, whereas non-hemolysed samples left at room temperature (22 degrees C) for 3 days were significantly lower, which might be due to a statistical type 2 error. No differences in concentration between serum and plasma i.r. inhibin were demonstrated. In conclusion, i.r. inhibin is a very stable peptide hormone in both serum and plasma if drawn and handled under normal conditions.