Emerging Evidence and Critical Issues with the Use of Single-Drop Capillary Blood for the Measurement of Hemoglobin Concentration in Population-Level Anemia Surveys

Accurate and precise measurement of hemoglobin concentration is critical for reliable estimations of anemia prevalence at the population level. When systematic and/or random error are introduced in hemoglobin measurement, estimates of anemia prevalence might be significantly erroneous and, hence, limit their usefulness. For decades, single-drop capillary blood has been the most common blood source used for the measurement of hemoglobin concentration in surveys, especially in low-income and middle-income countries. In this study, we highlight historical and emerging evidence that single-drop capillary blood introduces a high degree of random error (variability) to hemoglobin estimates, leading to less reliable estimates of anemia prevalence at the population level. At present, the best practice is to collect and use venous blood for measurement of hemoglobin with an automated hematology analyzer, following standard operating procedures and quality assurance measures. Where use of an automated analyzer is not possible, the analysis of venous blood in a point-of-care hemoglobinometer by trained phlebotomists or specimen collectors should be considered. A forthcoming systematic review will provide additional evidence on the accuracy and precision of single-drop capillary blood for hemoglobin assessment. In the meantime, we raise caution when using single-drop capillary blood for hemoglobin measurement as it can result in inaccurate hemoglobin estimates and less reliable anemia prevalence estimates.