Continuous Glucose Monitoring Is Not Ready for the Diagnosis of Prediabetes

With the growing availability of over-the-counter continuous glucose monitors, the question arises whether Continuous Glucose Monitoring (CGM) can be used to diagnose prediabetes. Traditionally, prediabetes is diagnosed using the oral Glucose Tolerance Test, a test with poor reproducibility. In a study from Singapore, there was large overlap between Ambulatory Glucose Profiles of people with prediabetes and normoglycemia. The optimal threshold of 5.64% Time above 140 mg/dL, the best discriminator, yielded 88% specificity and 48% sensitivity, indicating insufficient discriminatory value in many cases. In a study from Stanford, administration of a 75-gram oral glucose load while wearing CGM showed poor agreement with venous sampling between the category outcomes normoglycemia, prediabetes and diabetes. Future large cohort studies and AI may improve this situation. But for the moment, when a question of prediabetes arises, the most practical answer is to measure HbA1c, which allows for an elegant classification of normoglycemia, prediabetes and diabetes.