Evaluation of CGM performance studies should follow an identical study design, including sufficient swings in glycemia. At least a part of the study participants should wear two identical CGM sensors in parallel. All data available should be used for evaluation, both by MARD and PARD, a good PARD value being a precondition to trust a good MARD value. Results should be analyzed and presented separately for clinically different categories, e.g., hypoglycemia, exercise, or night and day.

Prediction algorithms should be used to provide real-time CGM readings more consistent with simultaneous measurements by SMBG. Patient specificity may play an important role in improving prediction quality.

Currently three manufacturers from the United States have needle-type systems for real-time continuous glucose monitoring (CGM) on the market. Each of these manufacturers has introduced new generations of its respective CGM system to the market over the past decade; each new generation has shown substantial improvements in analytical performance, size, handling, and so on (Dexcom G4® Platinum, Abbott FreeStyle® Navigator II [currently not available in the US market], Medtronic Enlite®).1 As well, one manufacturer from the European Union (EU) has announced a new product. 2While the rapid development and subsequent improvement are quite positive for clinical usage, they hamper the evaluation of the safety and efficacy of such systems in the classic evaluation setting, that is, the performance of clinical head-tohead studies, which typically require years for completion.One parameter often used to characterize the analytical performance of CGM systems is MARD, the mean (sometimes also the median value is used) absolute relative difference between the CGM readings and the values measured at the The ongoing progress of continuous glucose monitoring (CGM) systems results in an increasing interest in comparing their performance, in particular in terms of accuracy, that is, matching CGM readings with reference values measured at the same time. Most often accuracy is evaluated by the mean absolute relative difference (MARD). It is frequently overseen that MARD does not only reflect accuracy, but also the study protocol and evaluation procedure, making a crossstudy comparison problematic.

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