Comparison of Anemia Screening Methods Using Paired Venous Samples in Women of Reproductive Age in Southern India

Comparison of venous and pooled capillary hemoglobin levels for the detection of anemia among adolescent girls

Introduction

Blood source is a known preanalytical factor affecting hemoglobin (Hb) concentrations, and there is evidence that capillary and venous blood may yield disparate Hb levels and anemia prevalence. However, data from adolescents are scarce.

Objective

To compare Hb and anemia prevalence measured by venous and individual pooled capillary blood among a sample of girls aged 10-19 years from 232 schools in four regions of Ghana in 2022.

Methods

Among girls who had venous blood draws, a random subsample was selected for capillary blood. Hb was measured using HemoCue® Hb-301. We used Lin's concordance correlation coefficient (CCC) to quantify the strength of the bivariate relationship between venous and capillary Hb and a paired t-test for difference in means. We used McNemar's test for discordance in anemia cases by blood source and weighted Kappa to quantify agreement by anemia severity. A multivariate generalized estimating equation was used to quantify adjusted population anemia prevalence and assess the association between blood source and predicted anemia risk.

Results

We found strong concordance between Hb measures (CCC = 0.86). The difference between mean venous Hb (12.8 g/dL, ± 1.1) and capillary Hb (12.9 g/dL, ± 1.2) was not significant (p = 0.26). Crude anemia prevalence by venous and capillary blood was 20.6% and 19.5%, respectively. Adjusted population anemia prevalence was 23.5% for venous blood and 22.5% for capillary (p = 0.45). Blood source was not associated with predicted anemia risk (risk ratio: 0.99, 95% CI: 0.96, 1.02). Discordance in anemia cases by blood source was not significant (McNemar p = 0.46). Weighted Kappa demonstrated moderate agreement by severity (ĸ = 0.67). Among those with anemia by either blood source (n = 111), 59% were identified by both sources.

Conclusion

In Ghanaian adolescent girls, there was no difference in mean Hb, anemia prevalence, or predicted anemia risk by blood source. However, only 59% of girls with anemia by either blood source were identified as having anemia by both sources. These findings suggest that pooled capillary blood may be useful for estimating Hb and anemia at the population level, but that caution is needed when interpreting individual-level data.

Hemoglobin measurement in venous blood compared with pooled and single-drop capillary blood: a method-comparison study in a controlled and survey setting in Uganda among children and women

BACKGROUND

Standard practice for estimating anemia in population-based surveys is to use a point-of-care device to measure hemoglobin (Hb) in a single drop of capillary blood. Emerging evidence points to larger than expected differences in Hb concentration depending on the blood source.

OBJECTIVE

We evaluated use of different blood sources to measure Hb with a HemoCue 201+ analyzer compared with the reference method of venous blood tested with a Sysmex XN-450 hematology analyzer.

METHODS

Hb concentration in venous, pooled capillary, and single-drop capillary blood were collected in controlled (laboratory) and survey (Demographic Health Survey-8 pilot) settings in Uganda among children 6-59 mo and nonpregnant women 15-49 y. Venous and capillary blood collected from the same individual was tested using a HemoCue 201+ analyzer and the venous blood was also measured with a Sysmex XN-450 hematology analyzer. Agreement between measures was estimated using Lin's concordance correlation coefficient, Bland-Altman plots, and Deming regression. Means and prevalences were compared using paired t-tests and McNemar's tests, respectively.

RESULTS

The limits of agreement between Hb measured using a HemoCue 201+ analyzer and the reference method were lowest for venous (1.1-1.96 g/dL), followed by pooled capillary (1.45-2.27 g/dL), and single-drop capillary blood (2.23-3.41 g/dL). Mean differences were <0.5 g/dL across comparators. There were statistically significant differences in Hb concentration from both types of capillary blood. Anemia prevalence was lower in pooled capillary blood compared with the reference method.

CONCLUSIONS

The variability of Hb measured by capillary blood using the HemoCue 201+ analyzer is higher than venous blood but the extent to which this impacts the validity of Hb and anemia estimates requires further exploration. Future research is also needed to evaluate the implications of using venous compared with capillary blood in population-based surveys. This trial was registered at clinicaltrials.gov (NCT05059457).