| Objective1.The aim of this study is to adapt prenatal Down syndrome screening to dried blood spots(DBS).And to explore the feasibility of DBS with AFP, Total HCG,uE3 or with AFP,FreeβHCG.2.Through study on the prevision(within-run and between-run), recovery and the detection limit of DBS,we mean to develop a large scale prenatal DBS screening method.3.To explore the feasibility and clinical values of screening methods on DBS,we obtain the gestational-age-specific median values,and input it with the clinical information into the lifecycle software to get the risk.Methods1.The serum samples and DBS of 503 gravidas were collected from the obstetric clinics of Beijing union medical hospital and Haidian Maternal and Child Health hospital,from December,2008 to April,2009.Clinical informations were collected simultaneously.2.To explore the way of DS screening,we study the elution,perforation and stability of dried blood spot.3.Serum specimens and DBS obtained from 116 gravidas were analyzed by conventional methodology and by the adapted assays respectively. Precision(within-run and between-run),recovery and detection limits studies were conducted.4.Serum specimens and DBS obtained from all 503 second-triemester singleton pregnancies were analyzed with two methods.From the results, we obtain the gestational-age-specific median values,even to get the risk computed through the lifecycle software.5.Follow-up the pregnancy outcomes of the 503 gravidas to correct our results.Results1.There is no significant difference between AFP and FreeβHCG after eluting either for 1h or for 24h.2.The location of peforation can affect the measurement of AFP and FreeβHCG.3.AFP can keep stable for 28 days in room temperature,other than for 12 days in 35℃;FreeβHCG can keep stable for 6 days in room temperature,while for 3 days in 35℃.4.The within-run prevision of AFP,Total HCG,uE3 and FreeβHCG assays are 6.35-7.71%,6.2-12.4%,9.29-16.35%and 6.4-9.99%,respectively. Between-run prevision are 13.51-22.6%,6.38-37.88%,26.28-32.6%and 9.44-15.23%.The recovery rate of these markers are 85.82-104.39%, 74.47-104.11%,70.15-143.1%and 87.6-113.51%o5.There was a strong statistically significant correlation between the levels of these markers in serum specimens and in DBS(R=0.93,0.691, 0.863,0.974,respectively).For these analytes,the precision variances were compared to those presented by the manufacturer for serum samples.6.There are no significant discrepancy in DBS of peripheral blood and venous blood(P＞0.05);the markers testing value get higher from center to side(P＜0.05).7.Two potential protocols were drafted.One model was direct transforming the value of dried blood to the value of serum by regression analysis;and the other:Through calculating the corrected local gestational-age-specific MOMof dried blood assay,we get the risk value of patients by Lifecycle.Conclusions1.For dried blood spot,the elution of 1 hour is suitable.2.As quality control,the location of perofation on dried blood spot play a main role in assay.3.Dried blood spot for AFP and FreeβHCG assay can keep stable for 6 days in room temperature,and for 3 days in 35℃.4.There is a statistically significant correlation between the levels of AFP,Total HCG,uE3 and FreeβHCG in serum specimens and in DBS.5.It is feasible to use these DBS adapted assays with AFP,Free HCG in maternal serum screening programs.6.The detection limit of AFP and FreeβHCG are 1.51u/ml,0.65ng/ml respectively.7.There are no significant discrepancy in DBS of peripheral blood and venous blood.8.Obtaining of local gestational-age-specific median values is to ease the computation of DS risk with DBS.The other way of obtaining risk value with DBS is to transform the value of DBS to the value of serum.
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