Predictive value of cord blood hematological indices and hemoglobin Barts for the detection of heterozygous alpha-thalassemia-2 in an African-Caribbean population

Background: Cord blood hemoglobin Barts (HbBarts) and hemocytometric indices may be used for classification of newborns into those without alpha-thalassemia-2 (alpha alpha/alpha alpha) and with heterozygous alpha-thalassemia-2 (-alpha(3.7)/ alpha alpha). We investigated by logistic regression analysis whether the combination of HbBarts and hemocytometric indices improves classification compared with classification based on a single analyte. Methods: HbBarts percentages and hemocytometric indices were determined in cord blood of 208 consecutive newborns in Curacao (Netherlands Antilles). Of these, 157 had alpha alpha/alpha alpha and 51 had -alpha(3.7)/alpha alpha established by DNA analysis. Results: Between-group differences were significant for erythrocytes, mean cell volume, mean cell hemoglobin (MCH), mean cell hemoglobin concentration, platelets, hemoglobin F-o (HbF(o)), and HbBarts. The Legit equation of the logistic regression model, using MCH (pg) and HbBarts (%), was: 427164 + 5.7916(HbBarts) - 1.3110(MCH). A sensitivity of 100% was reached at a Legit value of -3.70. The corresponding specificity was 62.2%, and the predictive value of a positive test (PV+) was 46.3% (95% confidence interval, 37.0-55.7%). The relative information gains were as follows: 88% for the HbBarts-MCH combination, 26% for MCH (not significant), and 0% for HbBarts compared with the 24.6% -alpha(3.7)/alpha alpha prevalence. Conclusion: Combined use of cord blood HbBarts and MCH improves classification compared with classification based on single hemocytometric indices. (C) 1999 American Association for Clinical Chemistry