Blood-sweat glucose dynamics during oral glucose tolerance testing: temporal delays, variability, and implications...

Objective.Sweat has been proposed as a non-invasive alternative biofluid for glucose monitoring; however, its reliability as a physiological measurement remains unclear because the temporal and quantitative relationship between sweat glucose with blood glucose is not fully understood. This study is aimed at investigate the dynamics of blood and sweat glucose during a standard oral glucose tolerance test (OGTT) in healthy adults.Approach.Thirty-five healthy participants underwent a standard OGTT. Blood glucose was measured using a commercial glucometer, while sweat glucose was quantified via enzymatic colorimetric assay combined with a spectrophotometric analysis. Correlations, blood-to-sweat glucose ratios, and temporal delays between compartments were analyzed.Main results.A moderate positive correlation between fasting blood and fasting sweat glucose was observed after exclusion of outliers (n= 32;r= 0.44,p= 0.005). Peak glucose levels showed weaker associations (n= 35;r= 0.35,p= 0.02), accompanied by substantial inter-individual variability. Blood-to-sweat glucose ratios varied widely (fasting median: 55; post-OGTT median: 38). A pronounced temporal delay between peak blood and sweat glucose was observed, ranging from 10 to 90 min, with 60 min being the most frequent value.Significance.Sweat glucose reflects systemic glucose dynamics in a delayed and highly individualized manner. From a physiological measurement perspective, these findings indicate that sweat glucose cannot be considered a direct surrogate of blood glucose, particularly during dynamic glycemic changes. However, it may provide complementary information under controlled or baseline conditions. The results highlight fundamental limitations and considerations for interpreting sweat-based glucose measurements.