Carboxyhemoglobin - the forgotten parameter of neonatal hyperbilirubinemia

Neonatal hyperbilirubinemia is influenced by a wide variety of factors, one of which is hemolysis. Serious hyperbilirubinemia may lead to a kernicterus with detrimental neurologic sequelae. Patients suffering from hemolytic disease have a higher risk of developing kernicterus. Carbon monoxide (CO), a byproduct of hemolysis or heme degradation, was described by Sjöstrand in the 1960s. It is transported as carboxyhemoglobin (COHb) and exhaled through the lungs. We were interested in a potential correlation between COHb and total serum bilirubin (TSB) and the time course of both parameters.

We used a point of care (POC) blood gas analyzer and did a retrospective analysis of bilirubin and COHb data collected over a 60-day period.

An arbitrary cut-off point set at 2% COHb identified four patients with hemolytic disease of different origins who required phototherapy. In one patient with atypical hemolytic uremic syndrome (aHUS), COHb preceded the rise in bilirubin by about 2 days. Despite this displacement, there was a moderately good correlation of COHb with TSB levels <15 mg/dL (257 μmol/L) (r2: 0.80) and direct bilirubin (r2: 0.78) in the first patient. For all the four patients and all time points the correlation was slightly lower (r2: 0.59).

COHb might be useful as a marker for high hemoglobin turnover to allow an earlier identification of newborns at risk to a rapid rise in bilirubin.