Stability of free beta-hCG in the routine screening of Down syndrome in the first trimester of pregnancy.

Stability of free beta-human chorionic gonadotropin in maternal blood upon storage at ambient and refrigerator temperatures as well as stability under conditions simulating postal transport were studied. A group of 26 women in the first trimester of pregnancy were included in the study, blood samples were taken during the routine check-up. Blood samples were aliquoted stored in different conditions that should mimic the transportation and then analysed for free beta-hCG. No significant differences were found in the free beta-hCG levels in samples after 24 and 48 hours resp., stored in refrigerator (2-8 degrees C) without separation. In samples stored in laboratory temperature without separation the average concentration increased from 11 to 20%. Six blood samples were stored at 35 degrees C for 5 hours and then in laboratory temperature. In this group the average increase of results was from 14.3% to 132.2%. Separation of the sera for Down syndrome screening in 4 hours after withdrawal is necessary. Cooling during any storage, including transportation is highly recommended as the preanalytical phase has a high impact for the analysis.