Concordance Between Hemoglobin and Hematocrit Among Children and Pregnant Persons in National Health and Nutrition Examination Survey Data, 1999-2020.

Abstract

Background: Hemoglobin and hematocrit are the two most common biomarkers used to identify anemia in clinical settings, but their results do not always agree.

Objective: To examine agreement between hemoglobin and hematocrit in identifying anemia among children aged 1-<5 years and pregnant persons.

Methods: Pregnant persons and children aged 1-<5 years with hemoglobin and hematocrit results from the same whole blood sample in National Health and Nutrition Examination Survey (NHANES,1999-2020) were included. We used the Centers for Disease Control and Prevention (CDC) anemia cutoff values for children, pregnancy status, trimester, and smoking adjustments. We examined concordance of anemia, sensitivity, and specificity among those with anemia based on at least one test overall and by race/ethnicity, sex, and income level. Cohen's kappa was used to measure concordance.

Results: Analytic samples included 7,052 children and 1,437 pregnant persons, of which 1,119 had trimester data. Among children, anemia prevalence was 3.7% (95% CI: 3.1-4.3) based on hemoglobin and 5.5% (95% CI: 4.7-6.3) based on hematocrit. Among pregnant persons, anemia prevalence based on hemoglobin was 7.7% (95% CI: 5.9-9.5) and 12.4% (95% CI: 10.1-14.6) based on hematocrit. Kappa scores overall and by sociodemographic characteristics ranged from 0.64-0.75 (moderate concordance) among children and 0.53-0.78 (weak to moderate concordance) among pregnant persons. Among those with anemia on at least one test, 53.5% of children and 61.5% of pregnant persons had anemia based on both tests.

Conclusions: We found substantial discordance between the two biomarkers; about 50% of children and 40% of pregnant women were identified by only one of the two biomarkers. Because hemoglobin and hematocrit may be used interchangeably in the clinical setting, individuals with anemia may be missed, not receive treatment, and therefore be at higher risk of adverse pregnancy, birth, and developmental outcomes.