CGM May Improve Glycemic Control in Patients With Diabetes and Cystic Fibrosis

Findings from a systemic review suggest that continuous glucose monitoring (CGM) may be more effective than self-monitoring for managing glucose among patients with cystic fibrosis related diabetes (CFRD), a growing comorbidity among patients with CF since the life expectancy of the condition has improved.

Data from 17 studies of over 400 patients found that CGM was associated with improved glycemic control, with a 4.1 mmol/mol (0.4%) reduction in HbA1c after at least 6 weeks of use. Among the 138 patients using CGM, the weighted mean difference in HbA1c from baseline to follow-up was –3.9 mmol/mol (95% CI, –5.9 to –2.0; P < .0001) compared with –3.0 mmol/mol (95% CI, –7.5 to 1.5; P = 0.93) among the 278 patients who self-monitored their glucose

“Our findings are consistent with multiple systematic reviews evaluating data from randomised controlled trials in type 1 diabetes which have demonstrated that use of CGM is associated with improved glycemic control as evidenced by reduction in HbA1c when compared to SMBG,” wrote the researchers. “However, the magnitude of difference in HbA1c between CGM and SMBG groups was greater in our study than those reported in type 1 diabetes cohorts (–0.4% vs -0.26%) which indicate that our findings likely over-estimate CGM effect. Nevertheless, CFRD has distinct epidemiology, pathophysiology and management compared to type 1 diabetes, which could partly explain the observed differences.”

The researchers flagged that their analysis had a lack of head-to-head trials comparing CGM and self-monitoring, resulting in findings coming from studies with a high risk of bias, including confounding, selection, and publication bias.

A subgroup meta-analysis showed that glycemic control improved as duration of CGM use increased, with a weighted mean difference of –3.5 mmol/mol (95% CI, –5.6 to –1.5, p = .60) at 2-3 months, which increased to a weighted mean difference of -8.0 mmol/mol (95% CI, –15.6 to –0.3, P = –.96) at 4-6 months. There was 1 study that found a weighted mean difference of –4.8 mmol/mol (95% CI, –17.2 to 7.6) at over 7 months of follow-up.

The researchers of the analysis also explored the impact of the glucose monitoring approaches on pulmonary outcomes, noting that evidence is lacking. One study showed that among 7 patients using CGM, there was an overall reduction in FEV₁ of 4% while another showed an overall improvement of 8.4% in FEV₁ in 78% of 18 patients using CGM over a 12-month period. In the latter study, 53% of patients also reported needing fewer intravenous antibiotics and 38% reported needing fewer oral antibiotics.

“If use of CGM can improve glycemic control in CFRD then clarity around CGM targets are also needed. There is consensus on key CGM metrics and targets in type 1 diabetes with one of the core metrics being time in range specified as 70–180 mg/dL (3.9–10 mmol/L),” explained the researchers. “Microvascular complications are the principal disease-specific outcome in type 1 diabetes and studies have demonstrated correlations between time in range on CGM and complications. Although increasing life expectancy may influence diabetes-related manifestations, at present microvascular complications remain less common in CF. Therefore, we propose that pulmonary function should be considered the primary outcome and we found currently there is insufficient evidence to support disease-specific CGM targets in CFRD.”

Just 1 of the studies reported on patient satisfaction with their CGM system. In a study of 48 patients using a FreeStyle Libre device, 88% of users indicated that they agreed or strongly agreed the device was both easy and comfortable to use, and nearly all (98%) patients recommended future use of the CGM system and said the glucose trend arrow/scanning function was highly useful.

Reference

Kumar S, Soldatos G, Ranasinha S, Teede H, Pallin M. Continuous glucose monitoring versus self-monitoring of blood glucose in the management of cystic fibrosis related diabetes: a systematic review and meta-analysis. J Cyst Fibros. Published online July 27, 2022. doi:10.1016/j.jcf.2022.07.013