Table 2.
Common Metrics Used in the Analysis of Continuous Glucose Monitoring Data
| Term/metric | Detail and caveats |
|---|---|
| System performance | |
| MARD | Absolute deviation of CGM glucose measurement from a reference system. May be calculated for different ranges of plasma glucose (e.g., low) |
| Glucose control measures | |
| Mean blood (plasma) glucose (MBG, MPG); total area under glucose concentration curve | Mean of data over a defined period. Concatenates hyperglycemic and hypoglycemic excursions (cf HbA1c). CGM, like self-measured glucose, is reported as plasma glucose, but the term “blood” is often casually and incorrectly used |
| Glucose concentration curve area above a predefined threshold for a defined time period | Hyperglycemic deviation of glucose concentration multiplied by time; if the time base is the same as the time units, is the same as the average excursion; can be limited to a particular time of day, for example, postprandial; no weighting is given to more extreme levels |
| Glucose concentration curve area below a predefined threshold for a defined time period | Hypoglycemic deviation of glucose concentration multiplied by time; if the time base is the same as the time units, is equivalent to the average excursion; can be limited to a particular time of day, for example, nocturnal; no weighting is given to more extreme levels; |
| Time above or below some predefined threshold | Usually given as percentage of some defined time period; takes no account at all of the magnitude of the excursion |
| Time within some predefined range (time in range) | Usually given as percentage; choice of range open to manipulation to show good/poor results. Is to be reported both in time units and percentage of observed time. |
| Time to peak (nadir) and peak (trough) level | Conventional pharmacodynamic measures used in clinical laboratory challenge studies (e.g., meal challenges) |
| Number of excursions above or below some predefined level | A single excursion is time since crossing a threshold till return to that same threshold; fails to account for extended excursions |
| Low/high blood (plasma) glucose indices | Attempts to weight measurements for more extreme excursions; quantitative pathophysiological basis is uncertain |
| Glucose variability measures | |
| SD or CV of blood (plasma) glucose (SDBG, SDPG, CVBG, CVPG) | SD from mean level, and CV as percentage of mean level; can be restricted to a time of day; independent of direction of glucose excursions |
| Within-day, within-person glucose variability | A measure of mean changes usually over 24 h, but can be restricted to other periods |
| Between-day, within-person glucose variability (erratic glucose control) | May use variability between the average for each day in one person, but can be restricted to other time intervals (e.g., nocturnal, prebreakfast, and predosing) |
| MODD | Similar to previous parameter |
| MAGE | Direction-independent (absolute) deviation from the mean glucose level (or from some other level, baseline or predetermined), ignoring levels within 1SD |
| Graphical displays | Combined display by time of glucose control (mean of time) and between-person, between-day variability (study SD) at all time points; likely to create certain average basal and postmeal values due to between- and within-person variation in times of eating, thus flattening glucose excursions |
Other parameters have been proposed such as M-value, J-index, CONGA, ADRR, Lability/HYPO score, and GRADE, but have not been widely adopted.59,60
CV, coefficient of variation; MAGE, mean amplitude of glucose excursion; MARD, mean absolute relative difference; MODD, mean of daily difference; SD, standard deviation.