In some circumstances, elevated blood glucose levels can be indicative of medical concerns like insulin deficiency. People with type 1 diabetes are more susceptible to insulin deficiency since they have almost no ability to produce any insulin; therefore, they need to receive instruction on why and when to check for ketones (1). This is especially important if the individual is using an insulin pump. If ketones are present, then the higher blood glucose levels are a result of insulin deficiency, and corrective action should be taken immediately.
People with type 2 diabetes can experience hyperglycemia from a combination of insulin resistance and inadequate insulin secretion; in their case, extremely elevated glucose levels in combination with severe dehydration can result in hyperosmolar hyperglycemia, which may be aggravated by other extenuating health variables such as severe illness and infections (2). These individuals typically do not produce ketones; if ketones do exist, they may be due to dietary restriction, as opposed to insulin deficiency.
Most diabetes specialists teach people with type 1 diabetes to check for ketones when their blood glucose levels are consistently above 300 mg/dL (16.7 mmol/L), but they should check whenever they have unexplained hyperglycemia (≥200 mg/dL, or 11.1 mmol/L) that persists more than a couple of hours. Exercise should be postponed or suspended if blood ketone levels are elevated (≥1.5 mmol/L or 8.7 mg/dL), equivalent to moderate to large urine ketones, since blood glucose and ketones may rise further with even mild activity (3).
Insulin regimens paired with frequent blood glucose checks greatly diminish the chance of insulin deficiency developing, and significant levels of ketones are rarely found when performing blood or urine checks. In most circumstances, slightly elevated blood glucose levels should not interfere with exercise performance; however, some people report headaches, blurry vision, or lack of energy with even mild hyperglycemia, which may be reason enough to avoid physical activity until the glucose level improves. The health care facilitator must consider the ability of the individual to perform blood glucose and ketone testing and understand the complexity of the information.
In other situations, physical activity itself can raise normal blood glucose levels when performed at high intensity (4). The catecholamine response to very intense activity results in an exaggerated hepatic production of glucose for fuel, and after the activity is stopped, the insulin need can double during the post-activity period. If not corrected with insulin dosing in insulin users, this hyperglycemia may last for several hours before drifting down, or it may not decrease without additional insulin (5).
Those using insulin pump therapy may bolus with a small amount of insulin to address this physiological need. If the injecting insulin by syringe, an additional dose of short- or rapid-acting insulin can also be administered. The timing and amount of insulin given require careful consideration and monitoring to accomplish the desired blood glucose result. Individuals must consider any insulin remaining from their last injection or bolus in making subsequent adjustments to doses, as well as factor in the residual effects of the last bout of activity on blood glucose use (ie, postexercise enhanced insulin action). Regardless of the delivery method, this additional insulin dose can result in hypoglycemia and may not be advisable in all cases.
References:
Kamata Y, Takano K, Kishihara E, Watanabe M, Ichikawa R, Shichiri M. Distinct clinical characteristics and therapeutic modalities for diabetic ketoacidosis in type 1 and type 2 diabetes mellitus. J Diabetes Complications 2017;31:468-72. doi: 10.1016/j.jdiacomp.2016.06.023.
Umpierrez G, Korytkowski M. Diabetic emergencies - ketoacidosis, hyperglycaemic hyperosmolar state and hypoglycaemia. Nat Rev Endocrinol 2016;12:222-32. doi: 10.1038/nrendo.2016.15.
Riddell MC, Gallen IW, Smart CE, et al. Exercise management in type 1 diabetes: a consensus statement. Lancet Diabetes Endocrinol 2017;5:377-90. doi: 10.1016/S2213-8587(17)30014-1.
Fahey AJ, Paramalingam N, Davey RJ, Davis EA, Jones TW, Fournier PA. The effect of a short sprint on postexercise whole-body glucose production and utilization rates in individuals with type 1 diabetes mellitus. J Clin Endocrinol Metab 2012;97:4193-200.
Aronson R, Brown RE, Li A, Riddell MC. Optimal Insulin Correction Factor in Post-High-Intensity Exercise Hyperglycemia in Adults With Type 1 Diabetes: The FIT Study. Diabetes Care 2019;10-16. doi: 10.2337/dc18-1475. .