Performance characteristics of Elecsys free βhCG and PAPP-A for first trimester trisomy 21 risk assessment in gestational weeks 8+0 to 14+0

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Background: Screening for fetal trisomy 21 (T21) in the first trimester includes analysis of the serological markers pregnancy-associated plasma protein A (PAPP-A) and free β-choriogonadotropin (free βhCG). With the recent launch of these assays on the cobas e and Elecsys platforms, we investigated their clinical and analytical performance. Methods: We conducted a multicenter study in 5397 pregnancies including 108 cross-sectional collected repository cases with verified fetal T21 at 8–14 weeks of gestation. A technical validation of the Roche Elecsys® free βhCG and PAPP-A assays were performed, including method comparisons with the Brahms Kryptor®, PerkinElmer AutoDELFIA® and Siemens IMMULITE® assays. Furthermore a clinical validation including generation of assay specific medians from gestational age 8+0 to 14+0 weeks, and clinical test performance of risk assessment was performed. Results: The imprecision of the Elecsys free βhCG and PAPP-A assays was between 1.0% and 2.8%, and both assays showed correlation to Kryptor (free βhCG 0.981; PAPP-A 0.987), AutoDELFIA (free βhCG 0.995; PAPP-A 0.979) and IMMULITE assays (free βhCG 0.983; PAPP-A 0.983). With a cut off at 1:300 the overall sensitivity of the screening including nuchal translucency reached 94% for a 3% false positive rate. Conclusions: The Roche Elecsys free βhCG and PAPP-A are suitable and reliable assays for first trimester T21 risk assessment. Both assays were approved and recommended by the FMF.