Establish A New Method Detecting AFP And Free β-hCG Of Dried Blood Spots Specimens And Evaluate The Feasibility Of Using Dried Blood Filter Paper Method In Prenatal Screening For Down's Syndrome

Objective: Establish a laboratory method detecting the level of AFP and Freeβ-hCG of dried blood spots specimens on filter paper in the second trimester pregnancy. Then evaluate its feasibility in prenatal screening for Down syndrome.Methods: We detected the level of AFP and Freeβ-hCG of dried blood spots specimens collected from pregnant women in their second trimester with dissociation enhanced lanthanides fluoroimmunoassay (DELFIA). We also evaluated the imprecision, inaccuracy and constancy of this new laboratory method. After that, both dried blood spots specimens and conventional serum specimens were collected from 1320 subjects from three Maternal and Child Health Units in Shandong Province, east of China in 2007. We detected the level of AFP and Freeβ-hCG in both these two kinds of specimens and determined the risks of Down syndrome by calculating the medium and multiple of medium (MoM) through associate statistics software. We reviewed the outcome of risks for a single subject through dried blood specimens and conventional serum specimens. The results of high risk of Down syndrome from the serum specimens were used as the basis to determine the cut-off of positive results from dried blood specimens. Then we compared the screening results of these two kinds of methods and evaluated the concordance of them for screening Down syndrome through specificity, sensitivity, Youden Index and accuracy.Results: The levels of serum markers (AFP and Freeβ-hCG )of dried blood specimens under different circumstances(4℃or -20℃; kept for 1 month or 1 day) had no significant difference. The intra-lot and inter-day imprecision of AFP in dried blood specimen was 4. l%and 5. 2% respectively, as to Freeβ-hCG, the results were 5.0% and 5.8% respectively. The correlation coefficient of AFP level between serum and dried blood specimen was 0. 997 and Freeβ-hCG was even better correlated (0.999).The difference of screening results from the 1320 subjects using these two methods were not statistically significant. The sensitivity, specificity, Youden Index and accuracy was 94. 5%, 99. 7%, 94. 2%, 99. 4% respectively, using the serum method as the golden standard.Conclusion: We explored a new method to detect the level of AFP and Freeβ-hCG of dried blood spots specimens and confirmed the stability, accuracy and precision of this new method under different conditions. And this new method had good concordance with conventional serum method in Down syndrome screening. We could conclude that the feasibility of detecting AFP and Freeβ-hCG using dried blood spots specimens on filter paper for Down syndrome screening is affirmed by our study.