How well do Self-Monitored Capillary Glucose Measurements Predict the Mean Blood Glucose from 24-hour Continuous Monitoring in Endocrine Practice?

The mean blood glucose (MBG) level obtained from self-monitored capillary glucose (SMCG) data is a readily available metric of glycemic control for patients and their physicians. However, whether there is agreement between SMCG MBG levels and MBG levels obtained from 24-hour intensive glucose sampling is unclear. Therefore, we analyzed the relationship between MBG levels derived from SMCG data and glucose data derived from continuous glucose monitoring (CGM).SMCG and CGM were concurrently performed in 104 patients with diabetes and prediabetes over 3 to 6 days. MBG data obtained from SMCG and CGM were compared by standard correlation and Bland-Altman analyses.SMCG and CGM MBG data from the longest duration of sampling were highly correlated (r = 0.965; P.001). Single-day MBG estimates from both sources were also highly correlated, with r values ranging from 0.833 to 0.927. A SMCG MBG level of 166.1 ± 55 mg/dL (derived from 14.1 ± 4.6 samples) tended to slightly underestimate the concurrent CGM MBG level of 171.1 ± 56.4 mg/dL (derived from 1,063 ± 283 samples). The SMCG MBG was within 30 mg/dL of the CGM MBG in 94.6% of patients and within 15 mg/dL in 67% of patients. The difference between the estimates tended to increase with increasing SD of the MBG obtained from CGM (r = 0.38; P.0001).MBG estimated from SMCG is a reasonable estimate of a patient's CGM MBG over the same period of time and with caveats could be used as a practical guide for long-term glycemic control that can be considered in tandem with the patient's hemoglobin A1c in endocrine practice.