Comparison of capillary and venous hemoglobin determination among school-age children: insights from Zanzibar, Tanzania

Abstract

Objectives: There is apprehension regarding the agreement between capillary and venous hemoglobin (Hb) concentrations, which may have far-reaching consequences for global anemia prevalence estimates, heavily dependent on capillary Hb data. Methods: We investigated the discrepancies in Hb concentrations obtained from venous and capillary blood samples collected among school-age children in Zanzibar. Hb concentrations were measured in 810 children aged 10-19 years old. Both capillary and venous Hb measurements used a HemoCue 201+ analyzer (HemoCue, Angelholm, Sweden). Hb means, standard deviations, and anemia prevalence were analyzed using Stata. The means of the anemia categories were compared using paired t-tests. The agreement between capillary and venous Hb measurements was assessed using Pearson's correlation coefficients, a Passing-Bablok regression, and a Bland-Altman plot. Results: The correlation between paired measurements of capillary and venous Hb concentration was high, r=0.72 (p<0.001). The prevalence of anemia using venous samples was 20.5 %, and using capillary samples was 44.7 %. Mean Hb concentrations were higher in venous than capillary samples (mean ± SD: 12.994 ± 1.54 vs. 12.085 ± 1.36 g/dL, p<0.001). The mean difference between the methods is -0.909 g/dL, and the limits of agreement are (-3.065 - 1.247). Passing-Bablok regression analysis showed no evidence of systematic error between capillary and venous hemoglobin measurements. Conclusions: Capillary and venous hemoglobin measurements differ significantly; capillary Hb cannot replace venous Hb for accurate anemia assessment.