1. Association of ABO Incompatibility with RBC Indices of Cord Blood Unit Shu-Huey Chen, Marie Lin, Kuo-Liang Yang, Teng-Yi Lin, His-Hsiu Tsai, Shang-Hsien Yang, Yu-Hsun Chang, Yi-Feng Wu and Tso-Fu Wang Buddhist Tzu-Chi General Hospital, Hualien

2. Background and Objective :  major anti-A and anti-B antibodies in blood group B and A individuals are IgM; antibodies in group O individuals mostly IgG. The only immunoglobulin transferred from mother to fetus via the placenta is IgG.  Maternal-fetal ABO incompatibility causes neonatal hyperbilirubinemia.  Hb, Hct and RBC for cord blood units are lower and erythroblast higher for maternal-fetal ABO incompatible dyads than for compatible dyads.  CBU Hb, Hct and, RBC values are part of the routine data collected by all cord blood banks. We probably can use these RBC indices as a reference for predicting ABO HDN.

3. Material and Methods Sep. 2001 to Nov. 2006 3688 healthy neonates Group I, II, III  Group I : Mother O infant A, B or AB. AO (baby group A, mother group O), BO (baby group B, mother group O) and ABO (baby group AB, mother group O) subgroups.  Group II : Mother A infants B or AB and mother B infants A or AB  Group III : All other maternal-fetal blood type pairs were considered ABO compatible We compared the means Hb, Hct, RBC and erythroblast values for the infants’ CBUs among these three Groups including the subgroups of Group I.

4. Comparison of the mean Hb, Hct, RBC, nRBC ratio, maternal age, gestational age, cord blood volume and cord blood weight across Group I, II and III Group Ⅰ (555) Group II (326) Group III (2807) p Gender M/F (%)52.1/47.944.8/55.252.5/47.50.38 Vaginal/CS (%)74.1/25.975.8/24.272.3/27.70.25 RBC(×10 6 /μL)3.013.113.14<0.001 Hb (g/dL)10.610.810.9<0.001 Hct (%)35.135.736.2<0.001 nRBC(/100WBC)3.803.253.190.07 Mother age (y/o)29.929.8 0.92 Gestational age38.838.9 0.54 CBU weight (gm)141.2141.7141.00.84 Baby weight (gm)3257.53248.13251.80.92

5. Comparison of the mean Hb, Hct, nRBC ratio, and RBC between the AO and BO subgroups within Group I AO subgroup(305) BO subgroup(247) p value RBC (×10 6 /μL) 3.042.980.10 Hb (g/dL) 10.710.40.06 Hct (%) 35.434.70.04 nRBC(/100WBC) 3.783.840.93 Data are presented as means and compared by Student’s t-test

6. Dicsussion Ⅰ : Neonatal hyperbilirubinemia: multiple etiologies UGT1A1 gene variations, maturity of the neonatal liver, conditions that increase bilirubin production, conditions that increase enterohepatic circulation and breast feeding failure ABO incompatibility hemolytic disease mild  A and B blood type antigens are expressed at a low level on fetal red blood cells  antibodies are usually IgG2, which does not initiate red blood cell destruction  ABO antigens are present in many tissues and any IgG antibodies crossing the placenta are likely to become bound to placental tissue

7. Discussion II Desjardins L : 1704 infants with O mother, OA and OB cord blood Hb ↓ than OO → ABO incompatible infants showed some degree of hemolytic disease even though antibodies were not demonstrated by either the Coombs or eluate test. In our study, Group I infants have a lower mean Hb, Hct and RBC than the other two Groups

8. Discussion III Dufour and Monoghan : 0.8% of mothers of group A with infants having blood group B or AB and mothers of group B with infants having blood group A or AB showed laboratory evidence of hemolysis. Group II had lower Hb, Hct and RBC values than Group III but these differences did not reach statistical significance. Thus our results were consistent with Dufour and Monoghan’s findings.

9. Discussion IV Hemolysis in Group B infants is more severe than in Group A infants in some studies. Some other studies have reported no difference. In our study Hct for the AO group was higher than for BO group (35.4% and 34.7% in AO and BO subgroups, respectively) and only this difference was statistically significant (p=0.04).

10. Dicsussion V it seems likely that CBU Hb, Hct, reticulocyte count, direct Coombs test, eluate test and bilirubin result may help with predicting the severity of hyperbilirubinemia in ABO HDN. However, these laboratory results do not provide a reliable early diagnosis for ABO HDN because neonatal hyperbilirubinemia involves multiple etiologies.