Comparison of Glucose Measurements from Capillary Blood and Interstitial Fluid: A Correlation Versus Agreement Analysis of Published Data

Objective: Published data show a high correlation between glucose measurements obtained by capillary blood sampling and those from interstitial glucose sensors. However, correlation does not necessarily imply agreement. This study aimed to reanalyze published data to compare the correlation and agreement between these two methods. Methods: Using datasets of 708 paired glucose concentration values (mg/dL) measured by capillary blood glucose (CBG) monitoring strips and 2 interstitial glucose sensors (IGs), it was assessed whether the established high correlation between methods reflects actual agreement. The linear correlation and determination coefficients were calculated and Bland–Altman agreement analysis was performed. Results: The results confirmed a strong linear correlation between CBG and IG measurements. However, Bland–Altman analysis revealed that IG values ranged from approximately 41 mg/dL below to 74 mg/dL above CBG, indicating wide limits of agreement. Furthermore, agreement between methods decreased as glucose levels increased. Conclusion: Despite high correlation between CBG and IGs readings, significant discrepancies especially at higher glucose concentrations may compromise clinical accuracy. Agreement analysis is therefore critical when assessing alternative glucose monitoring methods. Cite this article as: Caldato CF, Santana NACd, Ecker LR, Teixeira CEC. Comparison of glucose measurements from capillary blood and interstitial fluid: A correlation versus agreement analysis of published data. Endocrinol Res Pract. 2026;30(1):9-16.