Effect of temperature on free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A concentration.

OBJECTIVE To examine the effect of the duration of storage of serum and whole blood at different controlled temperatures on the concentrations of both serum free-beta-human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A) in first-trimester screening for aneuploidies. METHODS The concentrations of free beta-hCG and PAPP-A were measured in samples collected from 10 pregnant women and stored as whole blood or serum for 1-8 days at 4, 20 or 40 degrees C. The concentrations measured were adjusted to take day-to-day variations into account and were expressed as a percentage of the values on day 0. In a second study involving 10 pregnant women, free beta-hCG was measured at 10 min and at 2, 4, 8 and 12 h after collection and storage at 30 or 40 degrees C, either as separated serum or as whole blood. RESULTS The change in the levels of PAPP-A in the separated serum at all three temperatures and in whole blood at 4 degrees C was always less than 10% throughout the 8 days of storage. In whole blood stored at 20 and 40 degrees C, the percentage variation was less than 10% only if the storage period was shorter than 4 days. The concentration of free beta-hCG was not altered by storage of either whole blood or separated serum at 4 degrees C throughout the 8 days of storage. At 20 degrees C, reliable results were obtained only if the maximum storage time was 2 days for separated serum and 1 day for whole blood. At 30 degrees C, reliable results were obtained only if the samples were analyzed within 2 h of collection, and at 40 degrees C the concentrations increased by more than 50% within 2 h and by about 500% after 1 day of storage. CONCLUSION In first-trimester screening for aneuploidies, analysis of blood samples should be undertaken within a few minutes of collection, otherwise the samples should be refrigerated at 4 degrees C throughout the interval between collection and analysis.