SUN-146 Glucose Clearance (GLCL) Using Continuous Glucose Monitoring (CGM)

Abstract

CGM is a useful tool in Type 1diabetes management. Its use reduces the frequency of insulin induced hypoglycemia and improves A1c values. Differences between venous, plasma, and interstitial fluid glucose values and “drift” in factory calibrated CGM sensors have rendered difficult quantifying glucose appearance and disappearance by CGM. This study applies a pharmacokinetic model to calculate GLCL. It assesses insulin responses to individual meals in a Type 2 diabetic patient weighing 79.1 kg treated exclusively with pre-meal Humalog and basal insulin Lantus. Method: The data included a standard breakfast of oatmeal, strawberries, blueberries, and cottage cheese (40 g available CHO, 15.5 g protein, 1.0 g fat) preceded by Humalog insulin administered by pen device 20-30 minutes prior to ingesting the breakfast. The “factory calibrated” FreeStyleLibre CGM determined the pre- and post-meal glucose concentration (return to baseline) revealing time (T) needed for meal-related glucose disposal. A “Volume of distribution” (Vd) was calculated as 15% kg body weight (interstitial fluid space) and the disappearance time (T) = duration of the rise and return to baseline of the glucose concentration. GLCL = Vd*Fd, where (Fd = 1/T). Vd = 133 dL. Because the interstitial fluid CGM values are reported as blood glucose values, the Vd was multiplied by 1.12 assuming a 12% difference between plasma and blood glucose values. Results: As expected, GLCL of the study breakfast depended on the pre-meal timing of the insulin bolus, the amount of insulin administered, and post-meal activity. It accounted for all of the post-hepatic glucose generated by the meal. The average of 9 such breakfasts: Average T = 293+/- 48 minutes; Vd = 133 dL; GLCL = 49 +/- 12 mL/min; GLCL/unit insulin = 4.19 +/- 1.03 mL/(min*unit insulin). CHO ingested/Insulin = 3397 +/- mg/unit. Post meal exercise increased GLCL. Conclusion: Calculating a GLCL adds a quantitative value to CGM that is useful in assessing glucose/insulin response to a known meal . It is specific to the individual patient. It only involves the time interval from baseline rise and return, kg body weight, and determination of corrected Vd. It is not influenced in a major way by drifting baseline values. It accounts for all the post-hepatic glucose appearance generated by the meal including concurrent glycogenolysis and gluconeogenesis. The clearance value was used to understand the timing and amount of insulin for the meal as well as the impact of exercise on mealtime insulin response . The GLCL/insulin ratio can be applied to any meal without carbohydrate counting.