Continuous glucose monitoring for diabetes: potential pitfalls for the general physician

A 31-year-old man presented systemically unwell with diabetic ketoacidosis (DKA). He was using an intermittently scanned continuous glucose monitoring (CGM) device that had been recording low or normal glucose readings for the 48 hours prior to admission. The sensor site had become infected, and we believe this soft tissue infection caused his CGM device to record falsely low glucose readings leading the patient to erroneously lower his insulin doses and take extra carbohydrates, precipitating DKA. CGM devices measure glucose levels in the interstitial fluid. When interstitial glucose readings do not match symptoms or expectations, a capillary blood glucose reading should be taken to correlate and impact treatment decisions. There will be an increase in patients presenting to hospital with CGM devices as the National Institute for Health and Care Excellence guidelines have recently been updated. We use this interesting clinical case to provide context for key learning points about CGM devices for the general physician.