P0763 - Suitability of Placental Blood Sample of Newborns for Pre-Transfusion Testing

Background: Placenta is usually discarded after delivery. Using placental blood samples for pre-transfusion testing reduces the amount of blood collected for initial laboratory tests from newborns and potentially reduces the risk of developing iatrogenic anemia. This study compares placental blood samples with heel stick samples from newborns.

Aims: This study aims to show concordance between heel stick and placental blood sample pairs for pre-transfusion testing of newborns, and to validate tube and gel methodology for placental samples.

Methods: Placental samples were collected for pre-transfusion testing at birth from 76 singleton and twins newborns admitted to Mother-Baby unit to compare the results with heel stick samples taken from the same newborns. This was approved by Institutional Review Board. Informed consent obtained from Newborn guardians. Gestational age ≥ 35 weeks, weight ≥ 2000g. ABO and RH typing, direct antiglobulin test with IgG (DAT) were performed on 76 sample pairs. Antibody screen tests were performed on 72 of these sample pairs, since four cases had insufficient volume for antibody screen. Both tube and gel methods were used to validate both methods for placental samples; the gel tests were performed by an Ortho ProVue Analyzer. Statistical analysis was performed using exact McNemar’s test for paired categorical data.

Results: This study shows 100% concordance in 76 sample pairs for ABO and Rh test results.
Regarding DAT test results, 64 (84%) of sample pairs were both negative, six (8%) of the sample pairs were both DAT positive, 92% concordance rate. Four (5%) of the placental sample tested DAT positive, while the corresponding heel stick sample were negative. Two (3%) of heel stick samples were DAT positive, while the placental samples were negative. Statistical analysis shows the lack of discordance between the sample pairs regarding DAT results (p=0.68).
In 10 of 12 DAT positive cases when either placental sample or heel stick sample were positive, maternal anti-A or anti-B antibodies coating newborns’ red cells were responsible for the positive DAT result. In two cases, both mothers and both newborns had B positive blood type and the antibody screen in serum of both mothers were negative. We hypothesize that non-specific IgG antibodies crossing the placenta from maternal circulation gave positive DAT results in both cases.
Of the 72 sample pairs tested for the presence of antibody, 70 sample pairs were both negative and 1 sample pair (1.4%) were both positive, 99% concordance rate. Only 1 (1.4%) sample pair gave discordant result, when the heel stick sample was positive for presence of antibody, while the placental sample was negative; p=0.999.

Conclusion: Placental blood is suitable for pre-transfusion testing and can replace heel stick samples. Also the gel method for ABO and Rh typing of placental blood samples is validated.