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.