95th
percentile were defined as having significant hemolysis. NeoNotes Journal Club
Andrew B. Kairalla MD, Editor
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ETCOc versus Coombs’ Test
Evaluation of the Direct Antiglobulin
(Coombs') Test for Identifying Newborns at Risk for Hemolysis as Determined by End-Tidal Carbon Monoxide Concentration (ETCOc); and Comparison of the Coombs' Test With ETCOc for Detecting Significant Jaundice. : Herschel M, Karrison T, Wen M, et al. Journal of Perinatology (July/August 2002), 22:341-347.660 consecutive term newborns had direct antiglobulin test (DAT)
screening and end-tidal carbon monoxide levels were obtained at 12±6 and at 24±6 hours
of age. Infants of nonsmoking mothers whose 12-hour exhaled carbon monoxide level was 95th
percentile were defined as having significant hemolysis.
Results: DAT was positive in 23 (3.5%). Using the 12-hour
end-tidal carbon monoxide 3.2 
l/l
(95th percentile) as reference (n=499 nonsmokers), the sensitivity of
the DAT was 38.5% (10 of 26) and specificity 98.5% (466 of 473) for the detection of
significant hemolysis. The PPV of the DAT for significant hemolysis at 12 hours was 58.8%
(10 of 17). For significant jaundice the PPV of end-tidal carbon monoxide was greater than
that for DAT (65.4% vs 52.9%), although not statistically so (p=0.25). The negative
predictive values were similar.
Conclusion: DAT fails to identify over half of the cases of significant hemolysis that are diagnosed by end-tidal carbon monoxide. A neonate with a positive DAT has about a 59% chance of having significant hemolysis. End-tidal carbon monoxide may also provide a more sensitive index for predicting significant jaundice.
Comment. The DAT can only be expected to pick up those cases of hemolytic disease that are antibody-mediated, whereas ETCOc would also be expected to screen for non-immune problems associated with increased hemoglobin metabolism such as spherocytosis, G6PD deficiency, polycythemia, excessive bruising, cephalhematomas, etc. It is therefore not surprising that DAT screening would miss some cases of "significant hemolysis" (as defined by high ETCOc levels). Neither test has a very high PPV for predicting significant jaundice (a more clinically significant endpoint
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