Carboxyhemoglobin levels as a predictor of risk for significant hyperbilirubinemia in African-American DAT + infants

Objectives:to compare the degree of hemolysis in a group of direct antiglobulin test (dat) positive (pos) african-american (aa) infants as measured by carboxyhemoglobin corrected (cohbc) for carbon monoxide in ambient air to a similar group of dat negative (neg) abo incompatible infants and a group without blood group incompatibility. to determine if cohbc is a better predictor of significant hyperbilirubinemia than dat status.study design:a prospective study of 180 aa infants from the well-baby nursery of an inner city community hospital, all of whose mothers were type o pos. infants (60) were abo incompatible dat pos, 60 were abo incompatible dat neg and 60 were type o+. blood for cohbc was drawn at the time of the infants’ initial bilirubin and the infants’ precise percentile on the bhutani nomogram was calculated.result:mean cohbc of type o+ infants was 0.76±0.21 and 0.78±0.24% for abo incompatible dat neg infants (p=0.63). mean cohbc for the abo incompatible dat pos infants was 1.03±0.41% (p<0.0001 compared with both type o and dat neg infants). optimal cutoff on the receiver operating characteristic curve for cohbc to determine the risk for being in the bhutani curve high risk zone was cohbc >0.90% (area under the curve(auc) 0.8113). this was similar to the auc of the receiver operating characteristic curve using any titer strength of dat pos as a cutoff (0.7960).conclusion:although not greatly superior to the titer strength of dat pos, cohbc is useful in determining if the etiology of severe hyperbilirubinemia is a hemolytic process.