Time With Rapid Change of Glucose

Abstract

Background: A variety of metrics are used to describe glycemic variation, some of which may be difficult to comprehend or require complex strategies for smoothing of the glucose curve. We aimed to describe a new metric named time with rapid change of glucose (TRC), which is presented as percentage of time, similar to time above range (TAR), time in range (TIR), and time below range (TBR).

Method: We downloaded glucose data for 90 days from 159 persons with type 1 diabetes using the Abbott Freestyle Libre version 1. We defined TRC as the proportion of time (%) with an absolute rate of change of glucose > 1.5 mmol/L/15 minutes (1.8mg/dL/min) corresponding to a minimum rate of change for glucose in the 3.9-10.0 mmol/L (70-180 mg/dL) range within 1 hour. TRC is related to the other glucose variability metrics: CV within day (CVw) and mean amplitude of glycemic excursion (MAGE).

Results: The more than 1.27 million glucose rates were t-location scale distributed with SD 0.91 mmol/L/15 min (1.1 mg/dL/15 min). The median TRC was 6.9% (IQR 4.5%-9.5%). The proportion of TRC with positive slope was 3.9% (2.6%-5.3%) and significantly higher than the proportion with negative slope 2.8% (1.5%-4.4%) P < .001. TRC correlated with CVw and MAGE (Spearman's correlation coefficient .56 and .65, respectively, P < .001).

Conclusion: TRC is proposed as an easily perceived metric to compare the performance of hybrid or fully automated closed-loop insulin delivery systems to obtain glucose homeostasis.

Keywords: continuous glucose monitoring; glucose rate of change; glucose variability; type 1 diabetes.

Figure 1.

An illustration of the calculation of TRC in a 24-hour period with a glucose value every 15 minute, except for 1 missing period. The number of 15-minute periods marked with red (n = 1 + 3 + 1 = 5) indicates a glucose rate of change > 1.5 mmol/L/15 min (27 mg/dL/15 min) and contributes to TRC+. The number of 15 minute periods marked with blue (n = 4 + 3 = 7) contributes to TRC− and indicates periods with a glucose rate of change < −1.5 mmol/L/15min. Of the 96 periods in 24 hours, only 93 periods in this example are available for rate of glucose calculation. TRC+ is (5/93) × 100 = 5.4%, TRC− is (7/93) × 100 = 7.5% and TRC is (12/93) × 100 = 12.9%.

Figure 2.

The cumulative distribution function (CDF) of pooled values of glucose rate of change (1 278 629 values) during 90 days from 159 persons with type 1 diabetes (black stepwise curve). The vertical dotted lines indicate a glucose rate of change of –1.5 mmol/L/15min and +1.5 mmol/L/15min (27 mg/dL/15min). The red curve is a t-location scale distribution and the blue curve is a normal distribution.

Figure 3.

A density histogram of rate glucose changes in intervals of 0.25 mmol/L/15min (4.5 mg/dL/15min). The blue curve is a normal distribution, SD 0.82 mmol/L/15min (15 mg/dL/15min) and the red curve is t-location scale distribution, SD 0.546 mmol/L/15min, (10 mg/dL/15min).

Figure 4.

Time with rapid glucose decrease with negative sign (TRC−) plotted against time with rapid glucose increase (TRC+). The line of identity is shown.

Figure 5.

Histogram of 15-minute intervals in a row with glucose rate of change > 1.5 mmol/L/15min (27 mg/dL/15 min).

Figure 6.

Time with rapid glucose rate of change (TRC) plotted against within day glucose coefficient of variation (CVw) and mean amplitude of glucose excursions (MAGE).