Alternate site (like) phenomenon: Rapid changes from hypoglycemic to hyperglycemic glucose levels in a clinical-experimental study in patients with type 1 diabetes

Intoduction: Monitoring of glucose changes by SMBG and by continuous glucose monitoring (CGM) systems is prone to certain delays during rapid changes in glycemia if the blood sample is collected at non-glabrous skin or in deeper layers of the skin.

Methods: Aim of this study was to evaluate the magnitude of such delays in a glucose-clamp study and during a standardized meal in 15 patients with type 1 diabetes (6 female/9 male; age 31±8 years (mean±SD); BMI 26,5±2,9kg/m²; HbA1c 7,1±0,9%; duration of diabetes 4±3 years). Venous blood glucose levels were measured continuously by means of the Biostator and in sc interstitial fluid by means of a microdialysis technique. In parallel, venous blood glucose levels were measured discontinuously by means of a laboratory method (reference values) and in capillary blood samples collected at 3 measurement sites (finger, lower arm, and abdomen) by blood glucose meters (one for each site; measured in duplicate). On the first study day blood glucose was clamped at different hyper- and hypoglycemic levels. On the next day, the second study day, slower changes in glycemia were induced by means of a carbohydrate-rich standardized meal.

Results: Venous blood glucose values measured with the lab system were comparable with the continuous recording with the Biostator. In contrast, the capillary measurement results are higher at all three measurement sites. This study shows that ISF glucose levels are higher in comparison to venous blood values during hyperglycemia on both study days but are identical to capillary blood glucose values measured in samples collected at the fingertips. Glucose levels in samples collected at the forearm and abdomen are identical to those collected at the fingertips during stable glycemic levels but run behind during rapid changes in glycemia: max. 30mg/dl after 60min.

Conclusion: Thus, the previously described AST phenomenon could be reproduced in relatively young patients with Type 1 diabetes. No pronounced AST-like phenomenon could be observed with CGM despite considerable rates of change of glycemia.