Effect of time and temperature of incubation of heparinized caprine blood on concentrations of progesterone detected in plasma

Blood samples from 12 pregnant does were collected in flasks containing heparin. Each sample was divided into 31 aliquots, the first of which was immediately centrifuged for plasma separation. Fifteen of the remaining aliquots from each goat were kept at 17 degrees C, while the remaining is were refrigerated at 4 degrees C. Centrifugation of these aliquots was carried out at half-hour intervals until completion of 6 h, and then at 8, 12 and 24 h post collection. The mean concentration of progesterone in the aliquots centrifuged initially was 4.0 +/- 0.3 ng/ml, and it was not significantly altered during incubation of the blood at 17 degrees C. In contrast, the concentrations of progesterone increased significantly to 5.0 +/- 0.3 (P < 0.05) during the first hour of incubation at 4 degrees C, remaining elevated most of the time. The stability of progesterone during incubation of heparinized caprine blood at 17 degrees C indicates that immediate centrifugation is not necessary. Refrigeration during the storage of blood samples is not recommended since progesterone levels are altered, probably due to separation of progesterone from the membranes of red blood cells during the hemolysis that is caused by incubation at low temperatures.