Background: A factor V506 Arg-Gln mutation is the most common inherited cause of thrombophilia in adults. This study compared a modified functional assay for APCR to PCR-based genetic assay in umbilical cord blood for the factor V mutation which causes activated protein C resistance(APCR).

Methods: APCR was determined using both a modified functional as well as a PCR assay. In the functional assay dilutions of infant plasma were diluted in dilutions of factor V deficient plasma. The PCR assay was performed on DNA isolated from whole blood. Samples from 31 healthy adults were used as controls.

Results: 115 umbilical cord samples were assayed. Both the modified functional as well as the PCR-based assays gave results in cord blood equivalent to those in adult samples. Overall, the incidence of APCR in cord blood was 6%. There was 100% correlation between the two methods. Although the incidence of APCR was higher in Hispanic infants as compared to White (11% versus 5%), and higher in infants with a positive as compared with negative family history of thrombosis (14% versus 5%), neither was significant.

Interpretation: APCR can be determined in neonates using either a modified functional or genetic assay. These assays can be used in future studies to assess the role of factor V mutation in newborn thrombosis.