CGM May Be Useful Diagnostic Tool for Diabetes in Cystic Fibrosis, but Data Scarce

A new review of studies comparing continuous glucose monitoring (CGM) with oral glucose tolerance tests (OGTT) suggests continuous monitoring would flag more people with cystic fibrosis as having cystic fibrosis-related diabetes (CFRD), but the authors said the existing research base is too fragmented to know how to ensure accurate diagnoses with CGM.

Previous research suggests that as many as half of people with cystic fibrosis will develop diabetes, and the comorbidity can lead to a number of complications, including higher infection risk, faster pulmonary decline, and ultimately higher mortality. Early detection of CFRD is considered critical, since treatment of CFRD can lead to improved lung function and lower mortality rates.

CGM is a technology that tracks patients’ blood glucose over time. It was developed to help patients with diabetes manage their disease, but corresponding author Helena Teede, MBBS, PhD, of Monash University, in Australia, explained along with colleagues that the technology could also be used, in theory, to help detect patients with CFRD, leading to earlier treatment and improved long-term outcomes.

In a new review article in the Journal of Clinical & Translational Endocrinology, Teede and colleagues analyzed the existing scientific literature to find studies comparing CGM to OGTT as tools to detect dysglycemia in people with cystic fibrosis.

The authors found a total of 19 studies that included CGM and OGTT metrics. Together, 416 patients were included in the studies. On CGM, hyperglycemia was defined as having at least one peak sensor glucose reading of at least 200 mg/dL, and dysglycemia was defined as at least one peak sensor glucose reading between 140 and 199 mg/dL.

“CGM hyperglycemia in people with normal or abnormal glucose tolerances was used to define an arbitrary CGM-diagnosis of diabetes,” Teede and colleagues explained.

Though the investigators sought to compare outcomes between CGM and OGTT diagnosis, Teede and colleagues said they opted not to characterize outcomes as being superior or inferior or as having higher or lower sensitivity, since there is not yet international consensus on the use of CGM to screen or diagnose people with CFRD, and since there is no third reference against which to compare CGM and the current gold standard, OGTT.

A comparison of the data in the 16 studies showed the relative risk of an arbitrary CGM diagnosis of diabetes was 2.92 compared to OGTT, but Teede and colleagues cautioned that the studies they analyzed were highly heterogeneous and prone to bias.

The investigators said the ability of CGM to capture long-term data makes it a useful tool to capture a spectrum of glucose abnormalities in people with cystic fibrosis. Still, they concluded that a single reading of 200 mg/dL on CGM is not sufficient to diagnose a patient with CFRD.

Teede and colleagues concluded that more studies are needed to better understand the role CGM could potentially play in monitoring and diagnosing diabetes in people with cystic fibrosis.

“To facilitate high-quality research in this field, firstly reporting of standardized CGM metrics and consensus on definitions for CGM measures of dysglycemia and hyperglycemia in PwCF would be helpful,” they wrote.

In addition, the authors said long-term prospective trials would help investigators better draw links between CGM measures and disease-specific outcomes. They added that data evaluating consumer and healthcare provider experiences would help in the development of guidelines and in the implementation of CGM into clinical practice.

Reference

Kumar S, Pallin M, Soldatos G, Teede H. Comparison of continuous glucose monitoring to reference standard oral glucose tolerance test for the detection of dysglycemia in cystic fibrosis: a systematic review. J Clin Transl Endocrinol. 2022;30:100305. Published 2022 Sep 27. doi:10.1016/j.jcte.2022.100305