Prenatal diagnosis of Down syndrome: study of correlations between two types of blood collection tubes

In the perspective of a future request of accreditation according to the NF EN 15189 standard of the sector of prenatal diagnosis of the trisomy 21 foetal, we compared the results obtained for AFP, hCG, free hCG, PAPP-A and for the risks, according to 2 types of blood collection tubes: sterile tube and sterile tube with inert gel barrier. For 107 patients, the study of the Passing-Bablok regressions between the results from the 2 kinds of tubes, showed perfect correlations for measured biochemical markers (AFP, hCG, free hCG and PAPP-A) as well as for the estimated risks. A patient who presented a higher risk of foetal trisomy 21 (risk at 1/244) for the serum from the sterile tube was not in the high-risk area for the serum from the sterile tube with inert gel barrier (risk at 1/295). The fact that these 2 values of risk are very close to the threshold fixed to 1/250 can probably explain the observed conflict. Working on sterile tube, this study confirms that the requests of prenatal diagnosis of the trisomy 21 foetal taken from tube with inert gel barrier which we receive of outer laboratories.