ABO incompatibility became the leading cause of neonatal jaundice due to maternal–infant blood incompatibility especially after the widespread prevention of rhesus alloimmunization, accounting for 15%–20% of all pregnancies and hemolytic disease develops in approximately 10% of such newborns. Almost exclusively occurs in infants with blood groups A or B who are born to blood group O mothers. This is due to the naturally occurring anti-A and anti-B antibodies formed in the serum of group O mothers are of the IgG isotype which can cross the placenta, in contrast to the anti-A and anti-B found in the serum of group B and A mothers, which are of the IgM isotype.
Although most cases of ABO HDN are mild and have jaundice as the only clinical manifestation, significant hyperbilirubinemia (HB) requiring intensive phototherapy (PT), exchange transfusion and, rarely, hydrops fetalis have been reported.
The American Academy of Pediatrics (AAP) recommends a thorough clinical assessment and preferably a biochemical screening of all newborns for jaundice before discharge, especially if they are discharged before the age of 72–96 h. Furthermore, in babies with ABO incompatibility, AAP advises cord blood sampling for blood group typing and Direct Coomb's test (DCT) before discharge (APP 2004).
DCT positivity and laboratory evidence of hemolysis vary among infants with ABO incompatibility. The severity may also vary between O–A and O–B-incompatible neonates.
Our aim in this study is to evaluate the effect of neonatal blood group and Coomb's test status on the severity of hemolysis and neonatal jaundice due to maternal-fetal ABO incompatibility. Furthermore, we aimed to evaluate the utility of 12-h Transcutaneous bilirubin (TcB) and first total serum bilirubin (TSB) values in predicting the need for PT and intensive PT in infants with ABO incompatibility. In addition, we wished to evaluate the predictive value of the maximum reticulocyte percentage in predicting the need for packed red blood cells (PRBC) transfusion and intravenous immunoglobulin (IVIG) therapy in newborn infants with ABO incompatibility.
MATERIALS AND METHODS
This retrospective study was conducted at King Abdulaziz Medical City, Riyadh, Kingdom of Saudi Arabia, covering a 1-year from June 2017 to June 2018. Newborn infants (gestational age ≥35 weeks) with blood groups A or B born to mothers with blood group O were included in the study. The study was approved by the local institutional review board.
The diagnosis of maternal-neonatal ABO blood incompatibility was made in the presence of indirect HB in a newborn infant with blood type A or B and maternal blood type O, in the absence of identified causes such as early and late neonatal sepsis (complete blood count and differential is done for all babies who have clinical HB needing PT as part of the jaundice workup, and all babies who display changes in white blood count whether high or low are subsequently undergo blood culture to roll out infections and commenced on intravenous antibiotics), cephalohematoma (all babies who display clinical jaundice have physical examination to look for cephalohematoma as a cause of jaundice), inherited metabolic diseases (which is done in all babies born in our institution after completing 5 full feeds to look for inborn errors of metabolism), and other hemolytic diseases such as glucose-6-phosphate dehydrogenase deficiency (all babies born in national guard hospital undergo G6PD screening in the cord blood sample at birth). Blood grouping including rhesus factor and DCT on the cord blood were performed routinely in infants born to mothers with blood group O.
The electronic medical records of all patients were reviewed. Demographic parameters such as gestational age, birth weight, and gender were documented. Need for PT, intensive PT as well as IVIG and PRBC transfusions were also recorded. Laboratory results including initial TSB, hemoglobin at birth, lowest hemoglobin values, and the maximum reticulocyte percentage were also documented. Transcutaneous bilirubin (TcB) level was obtained routinely in all infants born to blood group O-positive mothers within 12 h of age.
Pathologic HB requiring PT or exchange transfusion was defined as any serum indirect (unconjugated) bilirubin level needing treatment with PT during the 1st week of life, which was based on the 2004 AAP HB treatment guidelines.
Standard PT is provided at an irradiance of 8–10 microwatts per square centimeter per nanometer (mW/cm2 per nm). Intensive PT is provided at an irradiance of 30 mW/cm2 per nm or more (430–490 nm). For intensive PT, an auxiliary light source should be placed under the infant.
IVIG treatment was administered to patients to patients if the TSB continued to rise despite intensive PT by 8.5 umol/l/h or remains within 35–50 umol/l of the threshold for exchange transfusion after intensive PT. Severe anemia was diagnosed by a venous hemoglobin of <13 g/dl whereas, mild anemia is diagnosed if the hemoglobin level is between 13 and 15 g/dl.
Babies were followed up during their hospital stay; TSB, hemoglobin, and reticulocyte percentage were repeated based on the severity of the HB. In infants, who needed treatment with PT, the PT was discontinued if the TSB has fallen to a level of at least 35–50 umol/l below the PT threshold. TSB is always checked 12–24 h after discontinuation of the PT to check for rebound HB.
Postdischarge follow-up is arranged for high risk infants with ABO incompatibility for HB in a dedicated neonatal special laboratory clinic. In addition, high risk infants with ABO incompatibility were followed up at 2–3 weeks of age in our neonatology clinic with the measurement of hemoglobin level prior to clinic to check for late onset anemia.
Data were tested for normality and found to be normally distributed. Differences between DCT-positive/DCT-negative infants, infants with blood groups A and B were assessed for statistical significance using paired sample t-test for continuous variables and the Chi-squared test for categorical outcomes. Univariate logistic regression was used to examine the probability of developing adverse outcomes in infants with ABO incompatibility.
The predictive value of the 12-h TcB and initial TSB values in predicting the need for PT and intensive PT was measured using the area under the area under the receiver operator characteristic (AUROC) curve. In addition, the predictive value of maximum reticulocyte percentage in predicting the need for PRBC transfusion and IVIG therapy were measured using the area under the AUROC curve. The best cut off values were established for 12-h TcB, first TSB and maximum reticulocyte percentage by examining the coordinates of the ROC curves. P <0.05 was considered statistically significant. The analysis was performed using IBM SPSS Statistics for Mac, version 25 (IBM Corp.), USA.
Of 9000 inborn live births, 825 were ABO incompatible, an incidence of 9.2%. The O-A group accounted for 57.2% and the O-B group 42.8%. Four-hundred and five (49.1%) of the ABO-incompatible newborns required PT and 78 (9.5%) needed intensive PT. Eight percent of patients developed severe anemia with hemoglobin levels below 13 g/dl and a further 10.8% had mild anemia with hemoglobin levels 13–15 g/dl. Twenty-three (2.8%) infants had IVIG therapy and 24 (2.9%) had PRBC transfusions. Twenty-six infants (3.2%) were readmitted for PT following discharge. None required exchange transfusion [Table 1].
Three-hundred and seventy-nine (46%) were DCT positive. Gestational age at birth and birthweight was significantly higher in DCT-positive infants compared to DCT-negative infants (P < 0.001). Need for PT and intensive PT was significantly higher in DCT-positive infants compared to DCT-negative infants (P < 0.001). DCT-positive infants required more PRBC transfusions (5.3% vs. 0.9%, P < 0.001) and IVIG therapy (6% vs. 0.2%, P < 0.001) compared to DCT-negative infants. Severe anemia (11.6% vs. 4.9%, P < 0.001) and mild anemia (14% vs. 7.7%, P < 0.001) were both significantly higher among DCT-positive infants. The maximum reticulocyte percentage was significantly higher among DCT-positive infants (7% vs. 5%, P < 0.001). Furthermore, the length of hospital stay (P < 0.001) and rebound HB (P = 0.002) was significantly higher among DCT-positive infants. Out patients follow-up for jaundice and late onset anemia was significantly higher among DCT-positive infants (P < 0.001). There was no statistically significant difference in the rate of readmissions between DCT-positive and negative infants (P = 0.07) [Table 2].
There were no differences in gestational age at birth, birth weight, and gender between infants of blood group A and blood group B (P = 0.931, P = 0.474, and P = 0.952), respectively. Initial TcB (75 vs. 61, P ≤ 0.001) and initial TSB (109 vs. 100, P = 0.002) levels were significantly higher among infants with blood group B compared to those of blood group A. There was no statistically significant difference in the initial hemoglobin levels between the two blood groups; however, the magnitude of decline in hemoglobin and the maximum reticulocyte percentage were significantly higher in infants with blood group B (P < 0.012, P < 0.001, respectively). The proportion of infants with severe anemia (11.3% vs. 5.5%, P = 0.001) and mild anemia (12.7% vs. 8.9%, P = 0.001) was significantly higher among infants with blood group B. The mean length of hospital stay was significantly longer in blood group B infants (P = 0.009) [Table 3].
Sixty percent of the blood group B infants were DCT positive compared to 35% of blood group A infants (P < 0.001). Need for PT (62% vs. 39%, odds ratio (OR) (95% confidence interval [CI]) 2.6 (1.9–3.4), P < 0.001), intensive PT (17% vs. 4%, OR [95% CI] 4.8 [2.8–8.2], P < 0.001), IVIG therapy (5.4% vs. 0.8%, OR [95% CI] 6.7 [2.2–19.7], P < 0.001), and PRBC transfusions (4.2% vs. 2%, OR [95% CI] 2.3 [1.28–5.3], P = 0.039) was higher in infants with blood group B compared to blood group A. The proportion of infants with rebound HB after discontinuation of PT was significantly higher in infants with blood group B compared to blood group A (10.2% vs. 4.8%, OR [95% CI] 2.2 [1.3–3.8], P = 0.003). There were no statistically significant differences in readmissions for PT after discharge between infants of blood group B and A (4.5% vs. 2% P = 0.055). More infants with blood group B positive were followed up in outpatients for jaundice (35% vs. 23%, OR [95% CI] 1.9 [1.4–2.6], P < 0.001) and late onset anemia (23% vs. 17%, OR [95% CI] 1.4 [1.0–1.9], P = 0.029) [Table 4].
TcB measured at median age of 12 h was significantly predictive of the need for PT (AUROC = 0.867, 95% CI [0.843–0.892]) and intensive PT (AUROC = 0.917, 95% CI [0.881–0.952]). A cut off values for 12-h TcB of 73 predicted the need for intensive PT with 92% sensitivity and 70% specificity. In addition, a 12-h TcB of 59 predicted the need for any PT with an 87% sensitivity and 67% specificity [Table 5]. First TSB obtained at a median age of 19 h was predictive of the need for intensive PT (AUROC = 0.824, 95% CI [0.781–0.868]) but not of any PT (AUROC = 0.527). A cut off value of 110 first TSB was predictive of the need for intensive PT with an 81% sensitivity and 69% specificity [Table 5]. The maximum reticulocyte percentage was significantly predictive for both the need for IVIG therapy (AUROC = 0.978, 95% CI [0.963–0.993]) and PRBC transfusion (AUROC = 0.863, 95%CI [0.761–0.964]) [Table 6]. There was a significant correlation between first TcB and first TSB levels (R = 0.850, P < 0.001) [Figure 1].
We report a 9.2% incidence of ABO incompatibility in our population, less than what have been reported in previous studies with relatively smaller numbers (17.3% (14) and 14.8% (1) respectively). We have only included infants born at more than or equal to 35 weeks' gestation which might explain the lower incidence of ABO incompatibility in our study. The A-O group accounted for 57.2% and the B-O group for 42.8% which is similar to previous reports. In a study of more than 3300 newborn nursery admissions, 7% had HDN caused by ABO incompatibility, and the A-O and B-O groups accounted for 57.4% and 42.6%, respectively.
Four hundred and five infants (49%) with ABO incompatibility in our study had significant HB needing PT and only 9.5% needed intensive PT. This is significantly higher than what was reported in other studies. For example, in the study by Bhat and Kumar, 30.4% ABO-incompatible newborns showed significant hyperbilirubinemia and needed PT. Similarly, Sarici et al. reported significant hyperbilirubinemia within the first 5 days of life in 21.3% of cases whereas, another study found that only 9% of infants with ABO incompatibility required PT. In contrast, much higher incidence of significant HB (75%) was reported in a study from Sri Lanka among ABO incompatible newborns.
In our study, 46% of ABO-incompatible infants were positive for DCT. The frequency of DCT positivity among ABO-incompatible infants has not been reported in many studies and may be very different based on the DCT technique and population examined. Bhat and Kumar reported a lower frequency of 1.9% DCT positivity among the Indian infants but Chen et al. reported a higher frequency of 28.7% among Taiwanese infants. In a study from the UK, a higher DCT positivity of 33% and a higher proportion of Coomb's-positive than Coomb's-negative newborns becoming jaundiced was reported.
In our study, B-O incompatibility accounted for 42.8% of all ABO incompatibilities, similar to a recent study in infants of black ethnicity. The distribution of A-O and B-O incompatibilities differs according to the population studied, because some ethnic groups, such as African Americans and Asians have a higher incidence of the B blood group. For example, the prevalence of the B blood group is 20% among African Americans and 11% among European Americans.
In our cohort, B-O incompatibility was associated with a higher rate of severe HB compared to A-O incompatibility. Treatment with PT and intensive PT as well as the use of IVIG therapy and the need for PRBC transfusions were higher in B-O incompatible newborns. Similar to what have been reported in a small study from South Africa of 51 infants, where infants with B-O incompatibility needed more exchange transfusion compared to infants with A-O incompatibility. On the contrary, the Serbian cohort of Bujandric and Grujic, found a greater risk of severe neonatal hyperbilirubinemia and exchange transfusion in blood group A infant of blood group O mother compared to blood group B infants of blood group O mother. Nevertheless, two other large cohort studies found no differences in the severity of jaundice, frequency of positive DCT, duration of PT, number of exchange transfusions, or the need of IVIG therapy between infants with blood groups A and B born to mothers with blood group O. We have also shown that B-O incompatible infants had a higher rate of DCT positivity, greater magnitude of decline in the hemoglobin during hospital stay, and higher maximum reticulocyte percentage. Previous studies also suggested a positive correlation between B-O incompatibility and positive DCT among blacks. Nevertheless, studies involving nonblack populations did not find such an association. To the best of our knowledge, there is no data on the DCT positivity and infant's blood group from the middle east.
None of the neonates in the present study required exchange transfusion. In contrast, others have reported high exchange transfusion rates of up to 40%.
Mild anemia was detected in 10% of our patients with ABO incompatibility. This is less than what has been reported by another small study of 25 infants of whom 40% had mild anemia. On the other hand, severe anemia occurred in 8% of our patients which is higher than the previously reported 1% of cases of ABO HDN.
This study demonstrated that there was a strong correlation between initial TcB and initial TSB in newborn infants with ABO incompatibility. Furthermore, we have also demonstrated that the initial TcB when taken at 12 h of life is highly predictive of both the need for PT and intensive PT in ABO-incompatible newborns. Indeed, this high predictive value of the TcB suggests that TcB measurement in these high-risk infants is a reasonably accurate early screening device, before the initiation of PT. This finding adds merit to the conclusion that TcB testing is consistently and positively correlated with TSB values. We have also demonstrated that the maximum reticulocyte percentage was predictive of the need for both PRBC transfusions and IVIG therapy. To the best of our knowledge, the predictive value of the maximum reticulocyte percentage among ABO incompatible newborns was not reported in the literature.
Our study had some limitations. First, we have only studied term and late preterm infants with ABO incompatibility; thus, the outcome of ABO incompatibility in relation to DCT positivity and the infant's blood group as well as the relationship between initial TcB and initial TSB in extremely premature infants is unclear. Second, we have only assessed the TcB before commencing PT and we did not have data on the TcB values during and after PT in those infants who needed PT. Another limitation of our study is that infants included in the study were from an ethnically homogeneous population therefore, we were unable to assess the differences in outcomes of ABO incompatibility with different ethnicities. In addition, we did not assess the strength of DCT positivity which would have been valuable in predicting the severity of the HB in ABO-incompatible newborns.
In newborn ABO incompatibility, we have shown that blood group B and DCT-positive infants suffered significantly adverse outcomes. This highlights the need for early diagnosis and close monitoring of this high-risk group of infants with ABO incompatibility. Furthermore, TcB measurement can be a reliable method for predicting the severity of neonatal HB in term and late-preterm infants with ABO incompatibility. The predictive value of TcB could be applied to infants to determine whether PT should be commenced, without the need for blood sampling. The high reticulocytes count is predictive of the severity of ABO incompatibility as evidenced by the need for PRBC and IVIG transfusions.
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Conflicts of interest
There are no conflicts of interest.
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