A new method for the determination of carboxyhemoglobinin blood of newborns. Possible clinical implications of elevated levels

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Spectral differences between hemoglobin derivatives from adult-(HbA) and fetal-hemoglobin (HbF) make the accurate determination of carboxyhemoglobin (COHb) troublesome in blood of newborns. Only the newest dedicated instruments for the determination of COHb take these differences into account.However, since there are virtually no spectral differences between both hemoglobins in the deoxygenated state, reduction of neonatal blood with sodium dithionite eliminates that spectrophotometric error.Based on this principle, an easy, fast and accurate method for the determination of COHb in minimal amounts of blood was developed; equally well suited for blood of newborns and adults. The instrument used with this new method is a general purpose centrifugal clinical chemistry analyzer (COBAS-FARA, Roche, Basle, Switzerland).After the reduction of blood with sodium dithionite, a simple two component system (Hb and COHb) is formed, which can be spectrophotometrically quantitated by measuring at two suitable wavelengths, i.e., 579 nm and 534 nm. The COHb fraction is calculated with the help ofCOHb % = 177.73 · (A534/A579)-176.66Comparison with the OSM3 Hemoximeter (Radiometer A/S, Denmark) for 145 adult blood samples with varying COHb levels (0–30 %) yielded a mean difference in COHb % of about 0.06 % (SD = 0.38).For fetal blood (N = 63) about the same difference was found when the OSM3 was used in the so-called fetal mode, while comparison with the regular adult mode yielded a difference of about 3.1 %.This indicates that the new method is indeed not disturbed by the spectral differences between HbA and HbF.It is observed that even in apparently healthy newborns, from smoking mothers, an COHb value of about 5 % can be measured. However, one has to take into account that the reduction in oxygen transport capability by COHb is about three times the measured COHb value. On the other hand, critically ill newborns suffering from severe hemolysis not only have a very low total hemoglobin concentration, but also produce considerable amounts of carbon monoxide. If in addition the mother has, until delivery, smoked cigarettes, this can lead to a situation in which adequate tissue oxygenation of the newborn is almost impossible.