Is the masked continuous glucose monitoring system clinically useful for predicting hemoglobin A1C in type 1 diabetes?

BACKGROUND

The masked continuous glucose monitoring system (Masked-CGMS) differs from standard CGMSs in three ways: (1) there is no feedback to the user so that no immediate regimen changes can be made; (2) it can only be worn for up to 5 days; and (3) there are no alarms to warn of hyperglycemia or hypoglycemia. Since 2008 masked-CGMS has become popular for identifying reasons that a patient's hemoglobin A1C does not correlate closely with his or her capillary blood glucose measurements. To date only one study addressing the clinical utility of Masked-CGMS for improving A1C in diabetes has been published. No studies are available specifically examining the variability and correlation of Masked-CGMS and A1C.

SUBJECTS AND METHODS

We performed 156 Masked-CGMS studies (40 patients studied sequentially a maximum of four times each) in type 1 diabetes patients. We then analyzed the resulting interstitial glucose levels obtained from the Masked-CGMS compared with an A1C measurement performed within 1 week of the Masked-CGMS study.

RESULTS

There was a very low correlation between the A1C and the Masked-CGMS-derived mean interstitial glucose level. This statistic did not provide sufficiently predictive information to be clinically useful for changing an individual patient's intensive insulin therapy regimen.

CONCLUSIONS

Our data demonstrate that a very weak correlation exists between 5 days of masked CGMS and a concurrently measured A1C level. For the individual type 1 diabetes patient, this relationship would unlikely to be clinically useful in altering the individual's treatment regimen.