Introduction: Dried blood spot (DBS) sampling is a useful alternative to traditional venous blood collection, that can be conveniently and reliability used for measuring glycated haemoglobin A1c (HbA1c).
Objective: To assess whether the measurement of HbA1c in DBS samples provide results comparable to those obtained from traditional venous sampling.
Methods: Venous and capillary blood samples were collected from 115 adult participants. Capillary finger blood samples were collected on pieces of cellulose filter paper, which were immediately placed inside breathable envelopes, stored at room temperature, and processed on the same day (D0), four (D4), seven (D7) and fourteen (D14) days after collection. HbA1c was measured in whole venous blood (WB), capillary blood (capDBS) and WB placed on the filter paper (venDBS), by turbidimetric inhibition immunoassay. Raw and corrected DBS values (obtained by applying raw values to day-specific formulae derived from regression models) were compared to WB results using linear regression and cross-validation models.
Results: Eleven participants had type 1 diabetes, and 56 individuals and type 2 diabetes. Mean HbA1c levels in WB samples was 6.22±1.11%. Median intra-assay CVs were <3% for WB and capDBS on all days. Results from capDBS and venDBS were moderately or highly correlated to WB results, with R² above 0.85 in the linear regression analyses (except for results from D14 samples). Correction of capDBS and venDBS values by day-specific formulae reduced the difference between WB and DBS results. A cross-validation model showed that capDBS values on D0, D4 and D7 were close to the WB results, with narrow prediction intervals.
Conclusions: The measurement of HbA1c from DBS samples provide results that are highly correlated with WB samples, with clinically acceptable variation if measured up to seven days after collection. The measurement of HbA1c through DBS sampling may be considered in situations where traditional venipuncture is not available.