Validation of a New Protocol to Collect and Isolate Plasma from Pregnant Women for Noninvasive Prenatal Testing (NIPT)

Most laboratories use specialized tubes (e.g., Streck) to recover circulating cell-free DNA (ccfDNA) for noninvasive prenatal testing (NIPT). We validated a low cost, simple procedure for collecting NIPT samples in remote laboratories that avoids highspeed centrifugation. EDTA gel blood sampling tube allows simple separation of plasma from blood cells. Decanted plasma is filtered to remove cell debris. The procedure can be performed within a few minutes after the blood centrifugation step, and ccfDNA-grade plasma can be frozen for transportation.

We recruited 51 pregnant women and collected blood in one EDTA-gel Greiner tube and two Streck tubes. All tubes were centrifuged at 1600 g x 10 min within 6 h of sample collection. Plasma from EDTA tubes was poured into a syringe cylinder and filtered through a 0.45 µm Millipore filter. Plasma from Streck tubes was recovered with a pipette and one was filtered as above while the second was centrifuged at 16 000 g. The ccfDNA was isolated and NGS sequencing libraries were prepared and sequenced on an Illumina system. Fetal fractions were estimated using SeqFF. This study had a power of 79% to detect a decrease of 1% in fetal fractions with the new method.

We did not observe any significant difference between the three procedures for the fetal fraction nor for the quality or quantity of libraries produced.

EDTA-gel tubes with filtration provide high quality plasma for ccfDNA analysis and can be sent frozen to the NIPT laboratory. This is economical and it frees the laboratory of time-consuming steps.