Measuring capillary blood glucose concentration: Is the first blood drop really the right blood drop?

Capillary blood glucose (CBG) is fundamental for diabetes mellitus management. However, it is still unclear whether the first or the subsequent blood drops most accurately reflect patients' blood glucose levels.

128 healthy volunteers were included in this prospective cohort study from November 2021 to December 2021. Capillary blood glucose concentrations of the first four blood drops, measured using glucose meters were compared with venous blood concentrations of the respective donors, measured using an in-lab hexokinase method. ANOVA, the Spearman correlation coefficient and Bland-Altman plots were used to analyze the data.

The mean plasma glucose concentration was 90.46 mg/dl with an SD of ± 14.416 (5.02 ± 0.8 mmol/l). There were statistically strong correlations among the glucose concentrations of all capillary blood drops (correlation coefficients of r > 0.8). The first capillary blood drops showed the lowest mean difference to plasma blood glucose concentrations (+4.92 mg/dl; +0.27 mmol/l), followed by the third drop (+7.28 mg/dl; +0.4 mmol/l), second drop (+7.30 mg/dl; +0.4 mmol/l) and fourth drop (+8.87 mg/dl; +0.49 mmol/l).

There is a strong correlation and good agreement between the different capillary blood drops, making all blood drops equally suitable for blood glucose monitoring. In practice, the given setting (clinical or patient self-monitoring) should be considered upon choosing a specific blood drop.