Abstract
This cohort study evaluates whether continuous glucose monitoring (CGM) alert settings are differentially associated with glycemic control outcomes among people with type 1 and type 2 diabetes.
Introduction
Continuous glucose monitoring (CGM) is the standard of care for individuals with type 1 diabetes (T1D) and insulin-treated type 2 diabetes (T2D) due to robust evidence of improved glycemic management.1,2,3,4 Although real-time CGMs offer customizable alerts,5,6 their use is inconsistent and their association with glycemic control remains uncertain.7,8 We aimed to examine these associations to inform optimal alert utilization, particularly for primary care clinicians who increasingly prescribe CGMs but may be less familiar with alert settings.
Methods
This retrospective cohort study used the Dexcom G6 CGM report from a large US health care system. It was approved by the institutional review Board at NYU Langone Health (i22-00930) with a waiver of consent granted because the study involved a secondary analysis of existing electronic health record data. A generalized estimating equation model was used for analysis (eMethods in Supplement 1). Statistical analyses were conducted using SPSS Statistics version 31 (IBM Corp) and R version 4.6.1 (R Project for Statistical Computing). Due to multiple hypothesis testing, we corrected P values using false-discovery rate correction. Statistical significance was set at P < .05.
Results
A total of 2387 participants were included; 844 (35.4%) had T1D and 1521 (63.7%) had T2D. The mean (SD) age was 42.7 (21.1) years, and 1227 (51.4%) were women.
Table 1 presents the association between each glycemic alert and glycemic outcomes. Enabling the alert for low glucose levels was associated with lower percentage of time below range (TBR) of 54 to 70 mg/dL (to convert to millimoles per liter, multiply by 0.0555), TBR less than 54 mg/dL, and SD but higher percentage of time above range (TAR) of 180 to 250 mg/dL. Enabling the alert for high glucose levels was associated with lower average glucose level, glucose management indicator (GMI), SD, TAR greater than 250 mg/dL, and TAR of 180 to 250 mg/dL and higher percentage of time in range (TIR) and TBR of 54 to 70 mg/dL.
Table 1. Association Between Each Glycemic Alert and Glycemic Outcomesa.
| Metric, by type of diabetesb | Alert setting, mean (SE)c | Model 1d | Model 2d | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Enabled | Disabled | β (95% CI)e | P value | FDR-corrected P valuef | β (95% CI)e | P value | FDR-corrected P valuef | P for interaction | FDR-corrected P valuef | |
| Low (12 055 alerts [93.6%] on; 819 [6.4%] off) | ||||||||||
| Average glucose level | ||||||||||
| Total | 174.61 (0.81) | 172.35 (1.91) | 2.26 (−1.49 to 6.02) | .24 | .37 | 6.72 (−1.31 to 14.75) | .41 | .56 | .04 | .09 |
| T1D | 174.94 (0.99) | 170.54 (2.16) | 4.40 (0.24 to 8.56) | .04 | .09 | 3.62 (−0.67 to 7.20) | .11 | .21 | NA | NA |
| T2D | 172.38 (1.27) | 187.15 (8.12) | −14.77 (−31.32 to 1.77) | .08 | .16 | −12.59 (−26.53 to 1.35) | .08 | .16 | NA | NA |
| GMI, total | 7.45 (0.02) | 7.39 (0.05) | 0.06 (−0.04 to 0.16) | .25 | .37 | 0.11 (0.001 to 0.22) | .84 | .91 | .06 | .13 |
| SD, total | 55.78 (0.41) | 57.98 (0.78) | −2.20 (−3.68 to −0.72) | .004 | .02 | −1.02 (−2.72 to 0.68) | .003 | .01 | .07 | .14 |
| TAR >250 mg/dL | ||||||||||
| Total | 14.19 (0.29) | 13.85 (0.75) | 0.34 (−1.14 to 0.20) | .65 | .76 | 0.63 (−0.77 to 2.02) | .19 | .31 | .04 | .09 |
| T1D | 15.15 (0.37) | 14.25 (0.75) | 0.91 (−0.49 to 2.30) | .20 | .31 | 0.95 (−0.42 to 2.33) | .18 | .30 | NA | NA |
| T2D | 11.67 (0.49) | 14.71 (1.64) | −3.04 (−6.36 to 0.29) | .07 | .14 | −3.16 (−6.52 to 0.21) | .07 | .14 | NA | NA |
| TAR 180-250 mg/dL, total | 26.60 (0.23) | 24.60 (0.52) | 2.00 (0.94 to 3.06) | <.001 | .005 | 2.36 (1.13 to 3.60) | .03 | .08 | .17 | .29 |
| TIR, total | 56.91 (0.50) | 58.22 (0.97) | −1.31 (−3.23 to 0.62) | .18 | .30 | −1.54 (−3.61 to 0.52) | .65 | .76 | .09 | .17 |
| TBR 54-70 mg/dL, total | 1.65 (0.05) | 2.09 (0.14) | −0.44 (−0.71 to −0.16) | .002 | .008 | −0.37 (−0.73 to −0.10) | .01 | .03 | .97 | .98 |
| TBR <54 mg/dL, total | 0.45 (0.12) | 0.75 (0.07) | −0.30 (−0.51 to −0.08) | .007 | .03 | −0.14 (−0.32 to −0.04) | .03 | .08 | .78 | .87 |
| Low repeat (3845 alerts [29.9%] on; 9029 [70.1%] off) | ||||||||||
| Average glucose level, total | 174.23 (1.32) | 174.51 (0.95) | −0.29 (−3.45 to 2.88) | .86 | .92 | −2.03 (−5.40 to 1.35) | .32 | .46 | .87 | .93 |
| GMI, total | 7.42 (0.03) | 7.45 (0.02) | −0.04 (−0.10 to 0.03) | .25 | .37 | −0.06 (−0.13 to 0.02) | .24 | .37 | .23 | .36 |
| SD, total | 56.33 (0.51) | 55.78 (0.52) | 0.55 (−0.90 to 2.00) | .46 | .61 | −0.71 (−1.93 to 0.51) | .81 | .89 | .16 | .28 |
| TAR >250 mg/dL, total | 13.80 (0.49) | 14.30 (0.32) | −0.50 (−1.58. 0.58) | .36 | .51 | −0.62 (−1.64 to 0.41) | .31 | .45 | .97 | .98 |
| TAR 180-250 mg/dL, total | 27.26 (0.36) | 26.15 (0.25) | 1.11 (0.30 to 1.92) | .007 | .03 | 1.45 (0.41 to 2.49) | .002 | .008 | .99 | .99 |
| TIR, total | 56.65 (0.62) | 57.12 (0.57) | −0.47 (−1.93 to 0.98) | .52 | .66 | −2.05 (−4.41 to 0.30) | .12 | .22 | .49 | .64 |
| TBR 54-70 mg/dL, total | 1.80 (0.07) | 1.64 (0.06) | 0.16 (−0.01 to 0.33) | .07 | .14 | 0.13 (−0.14 to 0.40) | .37 | .52 | .47 | .62 |
| TBR <54 mg/dL, total | 0.59 (0.04) | 0.39 (0.17) | 0.21 (−0.11 to 0.52) | .20 | .31 | 0.05 (−0.11 to 0.21) | .94 | .97 | .30 | .44 |
| High (10 616 alerts [82.5%] on; 2258 [17.5%] off) | ||||||||||
| Average glucose level | ||||||||||
| Total | 172.70 (0.81) | 182.43 (1.42) | −9.72 (−12.53 to −6.91) | <.001 | .005 | −7.07 (−10.11 to −4.03) | <.001 | .005 | .03 | .06 |
| T1D | 173.16 (1.01) | 180.18 (1.61) | −7.02 (−10.10 to −3.93) | <.001 | .005 | −7.55 (−10.48 to −4.61) | <.001 | .005 | NA | NA |
| T2D | 170.40 (1.22) | 185.43 (3.18) | −15.04 (−21.53 to −8.55) | <.001 | .005 | −15.04 (−21.34 to −8.73) | <.001 | .005 | NA | NA |
| GMI | ||||||||||
| Total | 7.40 (0.02) | 7.64 (0.04) | −0.24 (−0.31 to −0.17) | <.001 | .005 | −0.15 (−0.23 to −0.07) | <.001 | .005 | .01 | .03 |
| T1D | 7.43 (0.03) | 7.58 (0.04) | −0.15 (−0.24 to −0.07) | <.001 | .005 | −0.16 (−0.24 to −0.08) | <.001 | .005 | NA | NA |
| T2D | 7.33 (0.03) | 7.71 (0.07) | −0.38 (−0.53 to −0.23) | <.001 | .005 | −0.40 (−0.54 to −0.25) | <.001 | .005 | NA | NA |
| SD, total | 55.33 (0.42) | 59.01 (0.54) | −3.69 (−4.76 to −2.62) | <.001 | .005 | −3.17 (−4.40 to −1.95) | <.001 | .005 | .12 | .22 |
| TAR >250 mg/dL | ||||||||||
| Total | 13.53 (0.29) | 17.18 (0.62) | −3.65 (−4.85 to −2.44) | <.001 | .005 | −2.28 (−3.46 to 1.11) | <.001 | .005 | .04 | .09 |
| T1D | 14.47 (0.40) | 16.82 (0.65) | −2.35 (−3.55 to −1.15) | <.001 | .005 | −2.19 (−3.33 to −1.04) | <.001 | .005 | NA | NA |
| T2D | 11.04 (0.48) | 14.73 (2.29) | −3.69 (−8.39 to 1.02) | .12 | .22 | −4.13 (−8.26 to −0.002) | .05 | .11 | NA | NA |
| TAR 180-250 mg/dL, total | 26.20 (0.24) | 27.69 (0.36) | −1.49 (−2.29 to −0.70) | <.001 | .005 | −1.29 (−2.23 to −0.34) | <.001 | .005 | .07 | .14 |
| TIR | ||||||||||
| Total | 58.14 (0.44) | 53.30 (0.71) | 4.84 (3.40 to 6.28) | <.001 | .005 | 3.83 (2.03 to 5.63) | <.001 | .005 | .01 | .03 |
| T1D | 56.66 (6.40) | 53.47 (0.83) | 3.19 (1.54 to 4.84) | <.001 | .005 | 3.20 (1.66 to 4.74) | <.001 | .005 | NA | NA |
| T2D | 61.69 (7.56) | 56.10 (3.65) | 5.59 (−1.77 to 12.96) | .14 | .25 | 6.04 (−0.76 to 12.84) | .08 | .16 | NA | NA |
| TBR 54-70 mg/dL | ||||||||||
| Total | 1.72 (0.05) | 1.51 (0.07) | 0.21 (0.05 to 0.37) | .01 | .03 | 0.37 (0.13 to 0.61) | .04 | .09 | .01 | .03 |
| T1D | 2.18 (0.10) | 1.82 (0.10) | 0.36 (0.12 to 0.61) | .003 | .01 | 0.37 (0.12 to 0.62) | .004 | .02 | NA | NA |
| T2D | 0.89 (0.05) | 0.92 (0.11) | −0.02 (−0.23 to 0.19) | .84 | .91 | 0.10 (−0.20 to 0.35) | .59 | .72 | NA | NA |
| TBR <54 mg/dL, total | 0.47 (0.12) | 0.51 (0.05) | −0.04 (−0.27 to 0.19) | .71 | .82 | −0.05 (−0.27 to 0.17) | .94 | .97 | .49 | .64 |
| High repeat (277 alerts [21.6%] on; 10 096 [78.4%] off) | ||||||||||
| Average glucose level, total | 170.61 (1.70) | 175.23 (0.93) | −4.63 (−8.69 to −0.57) | .03 | .08 | −5.39 (−9.17 to −1.62) | .004 | .02 | .81 | .89 |
| GMI, total | 7.34 (0.03) | 7.47 (0.02) | −0.14 (−0.20 to −0.07) | <.001 | .005 | −0.16 (−0.24 to −0.09) | .003 | .01 | .22 | .34 |
| SD, total | 55.88 (0.61) | 55.93 (0.50) | −0.05 (−1.72 to 1.62) | .95 | .97 | −1.95 (−3.44 to −0.48) | .12 | .22 | .20 | .31 |
| TAR >250 mg/dL, total | 12.59 (0.47) | 14.55 (0.31) | −1.96 (−2.95 to −0.97) | <.001 | .005 | −2.45 (−3.44 to −1.46) | <.001 | .005 | .95 | .97 |
| TAR 180-250 mg/dL, total | 26.35 (0.42) | 26.49 (0.24) | −0.15 (−1.03 to 0.74) | .75 | .85 | −0.10 (−1.19 to 1.00) | .75 | .85 | .61 | .73 |
| TIR, total | 58.04 (0.69) | 56.82 (0.53) | 1.21 (−0.35 to 2.78) | .13 | .23 | 0.33 (−2.20 to 2.85) | .41 | .56 | .63 | .74 |
| TBR 54-70 mg/dL | ||||||||||
| Total | 2.14 (0.09) | 1.57 (0.05) | 0.56 (0.38 to 0.76) | <.001 | .005 | 0.57 (0.30 to 0.84) | <.001 | .005 | .02 | .06 |
| T1D | 2.56 (0.11) | 1.98 (0.11) | 0.59 (0.31 to 0.86) | <.001 | .005 | 0.59 (0.32 to 0.86) | <.001 | .005 | NA | NA |
| T2D | 1.29 (0.34) | 0.85 (0.05) | 0.44 (−0.22 to 1.09) | .19 | .31 | 0.64 (−0.12 to 1.40) | .10 | .19 | NA | NA |
| TBR <54 mg/dL, total | 0.70 (0.05) | 0.37 (0.15) | 0.33 (0.04 to 0.62) | .03 | .08 | 0.07 (−0.11 to 0.24) | .69 | .80 | .39 | .54 |
| Fall rate (4263 alerts [33.1%] on; 8611 [66.9%] off) | ||||||||||
| Average glucose level, total | 173.10 (1.09) | 175.02 (0.90) | −1.92 (−4.31 to 0.47) | .12 | .22 | −4.64 (−8.03 to −1.24) | .54 | .67 | .05 | .11 |
| GMI, total | 7.41 (0.03) | 7.46 (0.02) | −0.06 (−0.12 to 0.01) | .06 | .13 | −0.08 (−0.16 to 0.01) | .50 | .64 | .20 | .31 |
| SD | ||||||||||
| Total | 55.81 (0.46) | 55.97 (0.47) | −0.17 (−1.17 to 0.84) | .75 | .85 | −1.06 (−2.35 to 0.23) | .95 | .97 | .01 | .03 |
| T1D | 55.59 (0.58) | 60.04 (0.68) | −1.45 (−2.85 to −0.05) | .04 | .09 | −0.93 (−2.23 to 0.38) | .16 | .28 | NA | NA |
| T2D | 52.31 (1.31) | 47.68 (1.33) | 4.63 (0.10 to 9.17) | .05 | .11 | 4.35 (0.11 to 8.59) | .05 | .11 | NA | NA |
| TAR >250 mg/dL, total | 13.69 (0.44) | 14.38 (0.32) | −0.70 (−1.63 to 0.23) | .14 | .25 | −0.97 (−2.09 to 0.16) | .79 | .88 | .09 | .17 |
| TAR 180-250 mg/dL, total | 26.45 (0.35) | 26.47 (0.26) | −0.02 (−0.81 to 0.78) | .97 | .98 | 0.13 (−1.06 to 1.31) | .44 | .59 | .30 | .44 |
| TIR, total | 57.36 (0.57) | 56.90 (0.57) | 0.45 (−0.86 to 1.77) | .50 | .64 | 1.86 (−1.00 to 4.73) | .58 | .71 | .19 | .31 |
| TBR 54-70 mg/dL, total | 1.72 (0.10) | 1.66 (0.05) | 0.05 (−0.15 to 0.25) | .60 | .72 | 0.07 (−0.42 to 0.29) | .79 | .88 | .34 | .49 |
| TBR <54 mg/dL, total | 0.58 (0.03) | 0.40 (0.17) | 0.18 (−0.13 to 0.49) | .25 | .37 | −0.12 (−0.13 to 0.10) | .93 | .97 | .60 | .72 |
| Rise rate (3032 alerts [23.6%] on; 9842 [76.4%] off) | ||||||||||
| Average glucose level | ||||||||||
| Total | 170.80 (1.25) | 175.32 (0.83) | −4.52 (−7.03 to −2.01) | <.001 | .005 | −7.66 (−11.34 to −4.00) | .01 | .03 | .04 | .09 |
| T1D | 169.36 (1.51) | 175.81 (1.11) | −6.45 (−9.64 to −3.27) | <.001 | .005 | −6.00 (−9.75 to −2.18) | .002 | .008 | NA | NA |
| T2D | 172.21 (2.53) | 173.79 (1.28) | −1.59 (−6.66 to 3.48) | .54 | .67 | −1.33 (−6.32 to 3.66) | .60 | .72 | NA | NA |
| GMI, total | 7.36 (0.03) | 7.47 (0.02) | −0.11 (−0.18 to −0.05) | <.001 | .005 | −0.15 (0.22 to −0.07) | .003 | .01 | .28 | .42 |
| SD, total | 55.01 (0.53) | 56.15 (0.44) | −1.15 (−2.19 to −0.10) | .03 | .08 | −1.70 (−3.02 to −0.38) | .12 | .22 | .15 | .26 |
| TAR >250 mg/dL | ||||||||||
| Total | 12.94 (0.49) | 14.49 (0.30) | −1.55 (−2.54 to −0.56) | .002 | .008 | −2.61 (−3.93 to −1.29) | .02 | .06 | .03 | .08 |
| T1D | 12.61 (0.68) | 15.86 (0.43) | −3.24 (−4.82 to −1.66) | <.001 | .005 | −2.33 (−3.53 to −1.13) | <.001 | .005 | NA | NA |
| T2D | 13.04 (1.46) | 11.65 (0.55) | 1.39 (−1.86 to 4.64) | .40 | .55 | 1.11 (−1.86 to 4.07) | .47 | .62 | NA | NA |
| TAR 180-250 mg/dL, total | 25.98 (0.42) | 26.60 (0.25) | −0.62 (−1.52 to 0.30) | .19 | .31 | −0.33 (−1.26 to 1.93) | .17 | .29 | .06 | .13 |
| TIR, total | 58.39 (0.66) | 56.64 (0.53) | 1.75 (0.37 to 3.12) | .01 | .03 | 2.83 (0.38 to 5.27) | .04 | .09 | .30 | .44 |
| TBR 54-70 mg/dL, total | 2.03 (0.09) | 1.57 (0.06) | 0.45 (0.25 to 0.66) | <.001 | .005 | 0.46 (0.18 to 0.75) | <.001 | .005 | .36 | .51 |
| TBR <54 mg/dL, total | 0.66 (0.04) | 0.40 (0.14) | 0.26 (−0.01 to 0.53) | .06 | .13 | 0.12 (−0.02 to 0.25) | .02 | .06 | .90 | .95 |
| Urgent low (9246 alerts [73.9%] on; 1374 [26.1%] off) | ||||||||||
| Average glucose level, total | 174.95 (0.75) | 169.48 (1.58) | 5.47 (2.35 to 8.60) | <.001 | .005 | 5.20 (1.90 to 8.49) | .01 | .03 | .91 | .96 |
| GMI, total | 7.46 (0.02) | 7.33 (0.04) | 0.13 (0.05 to 0.22) | .001 | .005 | 0.11 (0.02 to 0.20) | .04 | .09 | .90 | .95 |
| SD, total | 56.24 (0.35) | 57.22 (0.72) | −0.98 (−2.38 to 0.42) | 0.17 | .29 | - 0.01 (−1.38 to 1.35) | .52 | .66 | .53 | .67 |
| TAR >250 mg/dL, total | 14.28 (0.30) | 13.19 (0.62) | 1.09 (−0.14 to 2.32) | .08 | .16 | 1.36 (−0.21 to 2.51) | .17 | .29 | .47 | .62 |
| TAR 180-250 mg/dL, total | 26.79 (0.22) | 24.39 (0.44) | 2.39 (1.49 to 3.29) | <.001 | .005 | 2.00 (0.96 to 3.05) | <.001 | .005 | .44 | .59 |
| TIR, total | 56.80 (0.42) | 59.25 (0.86) | −2.45 (−4.16 to −0.75) | .005 | .02 | −2.29 (−4.03 to −0.54) | .02 | .06 | .93 | .97 |
| TBR 54-70 mg/dL, total | 1.61 (0.05) | 2.27 (0.11) | −0.66 (−0.87 to −0.45) | <.001 | .005 | −0.57 (−0.84 to −0.29) | <.001 | .005 | .45 | .60 |
| TBR <54 mg/dL, total | 0.57 (0.03) | 0.71 (0.05) | −0.14 (−0.25 to −0.04) | .008 | .03 | −0.03 (−0.27 to 0.22) | .54 | .67 | .82 | .90 |
| Urgent low (9246 alerts [73.9%] on; 1374 [26.1%] off) | ||||||||||
| Average glucose level, total | 175.20 (0.76) | 169.19 (1.57) | 6.01 (2.89 to 9.14) | <.001 | .005 | 5.71 (2.34 to 9.09) | .01 | .03 | .59 | .72 |
| GMI, total | 7.47 (0.02) | 7.32 (0.04) | 0.14 (0.06 to 0.22) | <.001 | .005 | 0.12 (0.02 to 0.21) | .01 | .03 | .85 | .92 |
| SD, total | 56.37 (0.36) | 57.40 (0.75) | −1.03 (−2.50 to 0.45) | .17 | .29 | 0.74 (−1.57 to 1.31) | .51 | .651 | .62 | .74 |
| TAR >250 mg/dL, total | 14.38 (0.31) | 13.04 (0.61) | 1.34 (0.12 to 2.56) | .03 | .08 | 1.54 (0.33 to 2.75) | .05 | .11 | .70 | .81 |
| TAR 180-250 mg/dL, total | 26.91 (0.23) | 24.41 (0.45) | 2.50 (1.57 to 3.44) | <.001 | .005 | 2.09 (1.05 to 3.13) | <.001 | .005 | .99 | .99 |
| TIR, total | 56.54 (0.42) | 59.35 (0.87) | −2.81 (−4.55 to −1.08) | .002 | .008 | −2.66 (−4.50 to −0.83) | .02 | .06 | .75 | .85 |
| TBR 54-70 mg/dL, total | 1.62 (0.04) | 2.28 (0.11) | −0.66 (0.87 to −0.45) | <.001 | .005 | −0.53 (−0.80 to −0.25) | <.001 | .005 | .78 | .87 |
| TBR <54 mg/dL, total | 0.50 (0.08) | 0.75 (0.05) | −0.25 (−0.41 to −0.08) | .003 | .01 | −0.18 (−0.31 to −0.05) | .01 | .03 | .38 | .53 |
Abbreviations: FDR, false discovery rate; GMI, glucose management indicator; NA, not applicable; T1D, type 1 diabetes; T2D, type 2 diabetes; TAR, percentage of time above range; TBR, percentage of time below range; TIR, percentage of time in range.
SI conversion factor: To convert glucose to millimoles per liter, multiply by 0.0555.
The total sample comprised 2387 participants, including 1521 (63.7%) with T1D and 844 (35.4%) with T2D, with a total of 12 877 continuous glucose monitor (CGM) reports. The median (IQR) number of reports per person was 3 (2-6). Because a single participant could contribute multiple CGM reports, the descriptive statistics for CGM alert on and off status were summarized at the CGM report level. In contrast, the associations of CGM alert on and off status with glycemic metrics were analyzed at the participant level using generalized estimating equations (GEE) to account for repeated CGM reports from the same participant. The dates of the data used in this analysis were from September 2020 to April 2022. The analyses in this manuscript were reported on February 26, 2026 (original analyses), and July 16, 2026 (revised analyses).
The rows with data for total include results for T1D and T2D combined.
Mean (SE) values were estimated from the GEE models. The reported means are estimated marginal means (least-squares means) derived from the fitted GEE models, and the SEs are the corresponding robust SEs estimated by the model, which was calculated using robust variance estimators. Results from model 1 are reported, as the results for model 2 were similar.
Model 1 was not adjusted; model 2 was adjusted for covariates, including age, sex, type of diabetes, and the interaction between alert setting and type of diabetes. When a significant interaction between alert setting and type of diabetes was identified in the overall sample, indicating that the associations between each alert setting and each glucose outcome differed by participants with T1D and T2D, subgroup analysis by diabetes type was conducted. After adjusting the covariates, the conclusions still hold. The clustering strategy used in the GEE analyses: GEE models were used to account for the correlation among repeated measurements within participants. Individual participants (patient ID) were treated as the clustering unit, with repeated observations across time points. An unstructured working correlation matrix was used.
The β coefficient represents the mean difference between an alert on and alert off in the outcome associated with each predictor variable with/without controlling covariates.
Due to multiple hypothesis testing, P values were corrected using FDR correction.
Table 2 presents the association between the threshold level for the low and high alerts and glucose outcomes. Lower low alert thresholds (50-100 mg/dL) were associated with lower average glucose level, GMI, SD, TAR of 180 to 250 mg/dL, and TAR greater than 250 mg/dL but with higher TIR and TBR of 54 to 70 mg/dL. Lower high alert thresholds (100-400 mg/dL) were associated with lower average glucose level, GMI, SD, TAR greater than 250 mg/dL, and TAR of 180 to 250 mg/dL but with higher TIR and lower TBR of 54 to 70 mg/dL.
Table 2. Association Between the Threshold of Each Alert With Each Outcomea.
| Metric, by type of diabetesb | Model 1c | Model 2c | ||||||
|---|---|---|---|---|---|---|---|---|
| β (95% CI)d | P value | FDR-corrected P valuee | β (95% CI)d | P value | FDR-corrected P valuee | P for interaction | FDR-corrected P valuee | |
| Low (50-100 mg/dL) | ||||||||
| Average glucose level, total | 0.89 (0.53 to 1.26) | <.001 | .003 | 0.92 (0.59 to 1.25) | <.001 | .003 | .95 | .97 |
| GMI, total | 0.03 (0.02 to 0.03) | <.001 | .003 | 0.03 (0.02 to 0.03) | <.001 | .003 | .13 | .25 |
| SD, total | 0.15 (0.06 to 0.24) | .001 | .003 | 0.10 (0.01 to 0.19) | .03 | .078 | .07 | .16 |
| TAR >250 mg/dL, total | 0.26 (0.09 to 0.43) | .003 | .009 | 0.22 (0.03 to 0.15) | <.001 | .003 | .48 | .67 |
| TAR 180-250 mg/dL, total | 0.24 (0.20 to 0.28) | <.001 | .003 | 0.33 (0.17 to 0.50) | <.001 | .003 | .61 | .78 |
| TIR, total | −0.51 (−0.60 to −0.42) | <.001 | .003 | -.52 (−0.61 to −0.43) | <.001 | .003 | .77 | .88 |
| TBR 54-70 mg/dL | ||||||||
| Total | −0.04 (−0.05 to −0.03) | <.001 | .003 | -.06 (−0.07 to −0.05) | <.001 | .003 | <.001 | .003 |
| T1D | −0.06 (−0.07 to −0.04) | <.001 | .003 | -.06 (−0.07 to −0.04) | <.001 | .003 | NA | NA |
| T2D | −0.03 (−0.05 to −0.01) | <.001 | .003 | -.03 (−0.05 to −0.01) | <.002 | .003 | NA | NA |
| TBR <54 mg/dL, total | −0.01 (−0.02 to 0.01) | .41 | .62 | -.01 (−0.02 to 0.01) | .001 | .003 | .19 | .35 |
| Low repeat (0-240 min) | ||||||||
| Average glucose level, total | −0.06 (−0.13 to 0.004) | .07 | .16 | −0.08 (−0.16 to 0.007) | .08 | .18 | .92 | .97 |
| GMI, total | −0.002 (−0.004 to −0.001) | .002 | .006 | −0.002 (−0.004 to −0.001) | .04 | .10 | .71 | .84 |
| SD, total | 0.001 (−0.03 to −0.03) | .99 | .99 | 0.02 (−0.05 to −0.01) | .53 | .71 | .44 | .65 |
| TAR >250 mg/dL, total | −0.03 (−0.05 to −0.01) | .01 | .03 | −0.02 (−0.05 to −0.01) | .09 | .19 | .71 | .84 |
| TAR 180-250 mg/dL, total | 0.01 (−0.02 to 0.03) | .61 | .78 | 0.01 (−0.01 to 0.04) | .31 | .50 | .73 | .86 |
| TIR, total | 0.01 (−0.02 to 0.05) | .44 | .65 | −0.02 (−0.07 to 0.04) | .76 | .87 | .64 | .80 |
| TBR 54-70 mg/dL, total | 0.01 (.001 to .01) | .02 | .05 | 0.004 (-.002 to .01) | .12 | .24 | .51 | .69 |
| TBR <54 mg/dL | ||||||||
| Total | 0.004 (−0.002 to 0.01) | .16 | .30 | 0.003 (−0.001 to 0.006) | .46 | .66 | .04 | .10 |
| T1D | 0.003 (0.001 to 0.006) | .09 | .19 | 0.003 (−0.001 to 0.006) | .10 | .21 | NA | NA |
| T2D | −0.002 (−0.004 to −0.001) | .01 | .03 | −0.001 (−0.002 to 0.001) | .12 | .24 | NA | NA |
| High (100-400 mg/dL) | ||||||||
| Average glucose level, total | 0.21 (0.18 to 0.24) | <.001 | .003 | 0.22 (0.19 to 0.25) | <.001 | .003 | .20 | .36 |
| GMI, total | 0.01 (0.005 to 0.006) | <.001 | .003 | 0.05 (0.005 to 0.006) | <.001 | .003 | .07 | .16 |
| SD, total | 0.07 (0.056 to 0.073) | <.001 | .003 | 0.07 (0.05 to 0.08) | <.001 | .003 | .85 | .94 |
| TAR >250 mg/dL, total | 0.06 (0.05 to 0.08) | <.001 | .003 | 0.06 (0.03 to 0.09) | <.001 | .003 | .95 | .97 |
| TAR 180-250 mg/dL, total | 0.04 (0.03 to 0.05) | <.001 | .003 | 0.04 (0.01 to 0.05) | <.001 | .003 | .21 | .37 |
| TIR, total | −0.10 (−0.11 to −0.09) | <.001 | .003 | −0.10 (−0.12 to −0.09) | <.001 | .003 | .67 | .81 |
| TBR 54-70 mg/dL | ||||||||
| Total | −0.008 (−0.01 to −0.007) | <.001 | .003 | −0.008 (−0.01 to −0.007) | <.001 | .003 | <.001 | .003 |
| T1D | −0.009 (−0.1 to −0.007) | <.001 | .003 | −0.009 (−0.01 to −0.007) | <.001 | .003 | NA | NA |
| T2D | −0.005 (−0.007 to −0.002) | <.001 | .003 | −0.004 (−0.006 to −0.001) | .001 | .003 | NA | NA |
| TBR <54 mg/dL, total | −0.001 (−0.004 to 0.001) | .25 | .43 | −0.004 (−0.007 to −0.001) | <.001 | .003 | .16 | .30 |
| High repeat (0-240 min) | ||||||||
| Average glucose level, total | −0.02 (−0.06 to 0.02) | .27 | .45 | −0.02 (−0.06 to 0.02) | .33 | .52 | .98 | .99 |
| GMI, total | −0.001 (−0.002 to −0.0001) | .06 | .14 | −0.001 (−0.002 to −0.0001) | .22 | .38 | .50 | .69 |
| SD, total | 0.007 (−0.009 to 0.02) | .41 | .62 | −0.003 (−0.02 to 0.11) | .96 | .98 | .62 | .79 |
| TAR >250 mg/dL, total | −0.01 (−0.02 to 0.002) | .10 | .21 | −0.01 (−0.03 to 0.004) | .20 | .36 | .89 | .96 |
| TAR 180-250 mg/dL, total | 0.01 (−0.004 to 0.01) | .31 | .50 | 0.006 (−0.007 to 0.02) | .17 | .32 | .76 | .87 |
| TIR, total | 0.001 (−0.02 to 0.02) | .95 | .97 | 0.01 (−0.04 to 0.01) | .43 | .64 | .66 | .81 |
| TBR 54-70 mg/dL | ||||||||
| Total | 0.003 (0.001 to 0.005) | .01 | .03 | 0.003 (0.001 to 0.006) | .09 | .19 | .02 | .05 |
| T1D | 0.004 (0.002 to 0.007) | .01 | .03 | 0.003 (0.001 to 0.006) | .02 | .05 | NA | NA |
| T2D | 0.001 (−0.002 to 0.001) | .58 | .76 | 0.001 (−0.001 to 0.002) | .48 | .67 | NA | NA |
| TBR <54 mg/dL, total | 0.002 (0.001 to 0.005) | 0.11 | .23 | 0.001 (−0.001 to 0.003) | .75 | .87 | .21 | .37 |
| Fall rate (2-3 mg/dL/min) | ||||||||
| Average glucose level, total | 8.77 (3.24 to 14.29) | .002 | .006 | 7.80 (0.46 to 15.13) | .03 | .08 | .92 | .97 |
| GMI, total | 0.17 (.04 to 0.31) | .01 | .03 | 0.11 (.05 to 0.28) | .08 | .18 | .72 | .85 |
| SD, total | 5.01 (2.36 to 7.65) | <.001 | .003 | 3.95 (0.38 to 7.51) | .02 | .05 | .87 | .95 |
| TAR >250 mg/dL, total | 3.26 (1.12 to 5.40) | .003 | .009 | 2.10 (−0.39 to 4.41) | .05 | .12 | .91 | .97 |
| TAR 180-250 mg/dL, total | 0.07 (−1.96 to 2.11) | .95 | .97 | −1.71 (−4.14 to 0.72) | .59 | .77 | .05 | .12 |
| TIR, total | −3.13 (−6.31 to 0.06) | .05 | .12 | −0.51(−4.50 to 3.49) | .17 | .32 | .27 | .45 |
| TBR 54-70 mg/dL, total | 0.15 (−0.20 to 0.49) | .41 | .62 | 0.28 (−0.23 to 0.79) | .21 | .37 | .61 | .78 |
| TBR <54 mg/dL, total | 0.06 (−0.06 to 0.18) | .32 | .51 | 0.11 (−0.07 to 0.28) | .26 | .44 | .43 | .64 |
| Rise rate (2-3 mg/dL/min) | ||||||||
| Average glucose level, total | 19.50 (11.30 to 27.70) | <.001 | .003 | 17.52 (7.23 to 27.80) | <.001 | .003 | .80 | .90 |
| GMI, total | 0.47 (0.29 to 0.66) | <.001 | .003 | 0.46 (0.23 to 0.69) | <.001 | .003 | .93 | .97 |
| SD, total | 6.02 (2.30 to 9.73) | .002 | .006 | 6.93 (2.76 to 11.10) | .001 | .003 | .70 | .84 |
| TAR >250 mg/dL, total | 4.21 (1.60 to 6.82) | .002 | .006 | 4.22 (0.39 to 8.05) | <.001 | .003 | .69 | .83 |
| TAR 180-250 mg/dL, total | 4.98 (2.25 to 7.70) | <.001 | .003 | 4.86 (1.58 to 8.15) | <.001 | .003 | .63 | .80 |
| TIR, total | −8.48 (−12.66 to −4.31) | <.001 | .003 | −8.66 (−13.94 to −3.39) | <.001 | .003 | .58 | .76 |
| TBR 54-70 mg/dL, total | −0.48 (−1.04 to 0.08) | .10 | .21 | −0.39 (−1.13 to 0.34) | .10 | .21 | .49 | .68 |
| TBR <54 mg/dL, total | −0.10 (−0.26 to 0.06) | .21 | .37 | −0.007 (−0.20 to 0.18) | .34 | .54 | .39 | .60 |
| Urgent low (31-55 mg/dL)f | ||||||||
| Average glucose level, total | 6.89 (6.83 to 6.96) | <.001 | .003 | NA | NA | NA | NA | NA |
| GMI, total | −0.01 (−0.012 to −0.009) | <.001 | .003 | NA | NA | NA | NA | NA |
| SD, total | 2.19 (2.16 to 2.23) | <.001 | .003 | NA | NA | NA | NA | NA |
| TAR >250 mg/dL, total | 0.20 (0.17 to 0.22) | <.001 | .003 | NA | NA | NA | NA | NA |
| TAR 180-250 mg/dL, total | −0.50 (−0.52 to −0.48) | <.001 | .003 | NA | NA | NA | NA | NA |
| TIR, total | 0.36 (0.32 to 0.40) | <.001 | .003 | NA | NA | NA | NA | NA |
| TBR 54-70 mg/dL, total | −0.034 (−0.038 to −0.03) | <.001 | .003 | NA | NA | NA | NA | NA |
| TBR <54 mg/dL, total | −0.01 (−0.02 to −0.003) | .01 | .03 | NA | NA | NA | NA | NA |
| Urgent low soon repeat (15-30 min) | ||||||||
| Average glucose level, total | −0.02 (−0.29 to 0.24) | .86 | .94 | −0.02 (−0.32 to 0.29) | .46 | .66 | .35 | .55 |
| GMI, total | −0.001 (−0.007 to 0.006) | .78 | .89 | −0.002 (−0.01 to 0.006) | .46 | .66 | .80 | .90 |
| SD, total | −0.05 (−0.17 to 0.08) | .47 | .67 | −0.02 (−0.14 to 0.10) | .65 | .81 | .85 | .94 |
| TAR >250 mg/dL, total | −0.002 (−0.11 to 0.10) | .97 | .98 | −0.006 (−0.12,0.11) | .50 | .69 | .57 | .76 |
| TAR 180-250 mg/dL, total | −0.07 (−0.15 to 0.02) | .13 | .25 | −0.10 (−0.21 to 0.10) | .07 | .16 | .88 | .96 |
| TIR, total | 0.08 (−0.75 to 0.23) | .32 | .51 | 0.10 (−0.07 to 0.28) | .13 | .25 | .67 | .81 |
| TBR 54-70 mg/dL, total | −0.004 (−0.02 to 0.01) | .64 | .80 | 0.002 (−0.02 to 0.03) | .92 | .97 | .85 | .94 |
| TBR <54 mg/dL, total | −0.006 (−0.02 to 0.004) | .27 | .45 | 0.002 (−0.008 to 0.01) | .52 | .70 | .93 | .97 |
Abbreviations: FDR, false discovery rate; GMI, glucose management indicator; NA, not applicable; T1D, type 1 diabetes; T2D, type 2 diabetes; TAR, percentage of time above range; TBR, percentage of time below range; TIR, percentage of time in range.
SI conversion factor: To convert glucose to millimoles per liter, multiply by 0.0555.
The dates of the data used in this analysis were from September 2020 to April 2022. The analyses in this manuscript were reported on February 26, 2026 (original analyses) and July 16, 2026 (revised analyses). All urgent low repeat threshold sets are at 30 minutes, and urgent low soon threshold sets are at 55 mg/dL; therefore, it is not applicable to examine their association with glucose outcomes.
The rows with data for total include results for T1D and T2D combined.
Model 1 was not adjusted; model 2 was adjusted for covariates, including age, sex, type of diabetes, and the interaction between alert setting and type of diabetes. When a significant interaction between alert setting and type of diabetes was identified in the overall sample, indicating that the associations between each alert setting and each glucose outcome differed by participants with T1D and T2D, subgroup analysis by diabetes type was conducted. Model 2 was only adjusted for age and sex when conducting subgroups analysis by T1D and T2D. After adjusting the covariates, the conclusions still hold. Generalized estimating equation models were used to account for the correlation among repeated measurements within participants. Individual participants were treated as the clustering unit, with repeated observations across time points. An unstructured working correlation matrix was used.
The β coefficients represent the estimated increase or decrease in the outcome associated with a 1-unit increase in the alert threshold.
Due to multiple hypothesis testing, P values were corrected using FDR correction.
After adjusting covariates, the model cannot compute because after excluding missing data, the range for the variable of urgent low was 55 to 55 mg/dL.
After adjusting for age, sex, and type of diabetes, conclusions remained unchanged. We also found significant association between high alert on and TIR and TBR of 54 to 70 mg/dL in patients with T1D but not T2D.
Discussion
In this cohort study conducted in our large health system, most patients enabled their CGM alert, particularly the high and low alerts, which were associated with better glycemic outcomes. More aggressive (ie, lower) high glucose thresholds were consistently associated with more favorable glycemic profiles, including lower average glucose levels, GMI, SD, and TAR, and higher TIR. In contrast, low and urgent-low threshold settings showed mixed associations, primarily affecting hypoglycemia metrics. The association between high alert on and TIR and TBR of 54 to 70 mg/dL was found among patients with T1D but not T2D.
Consistent with prior literature from Europe,8 the low alert was the most commonly used feature. Users who enabled low, urgent low soon, and urgent low soon repeat alerts had a lower TBR compared with users who disabled each of these alerts, meeting the goals of these alerts. However, they had increased rates of TAR of 180 to 250 mg/dL, though reassuringly not TAR greater than 250 mg/dL. One possible explanation is overcorrection, resulting in rebound hyperglycemia. Alternatively, concern about hypoglycemia may lead some individuals to maintain higher glucose levels. However, these hypotheses remain speculative because behavioral factors were not assessed in this study. Future studies should examine behavioral factors and detailed glucose patterns. In contrast, enabling the high alert was associated with lower average glucose, GMI, and SD, and higher TIR. However, it was also associated with greater TBR of 54 to 70 mg/dL, signaling potential overtreatment of hyperglycemia and underlying fear of hyperglycemia. Additionally, the high alert on was associated with TIR and TBR of 54 to 70 mg/dL in patients with T1D but not T2D, which may reflect differences in diabetes management, glycemic patterns, or responsiveness to CGM high alerts between T1D and T2D.
This study has several limitations. As an observational analysis, causality cannot be inferred, and the associations may reflect residual confounding or reverse causation, as patients using CGM alerts may be more engaged in diabetes self-management, receive more education, or have greater clinician involvement. Treatment information, including use of automated insulin delivery systems, was unavailable and may have confounded the results. We focused on the Dexcom G6, which accounted for 98.7% of CGM devices, although the findings are likely applicable to other CGMs with alert features. This is, to our knowledge, the first study to examine the association between CGM alert settings and glucose outcomes using empirical data from a large academic medical center. Our findings suggest that individualized alert thresholds may be associated with glycemic outcomes and patient safety, supporting further evaluation of individualized CGM alert settings.
eMethods
Data Sharing Statement
References
- 1.American Diabetes Association Professional Practice Committee for Diabetes . 7. Diabetes technology: standards of care in diabetes—2026. Diabetes Care. 2026;49(suppl 1):S150-S165. doi: 10.2337/dc26-S007 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Wilson A, Morrison D, Sainsbury C, Jones G. Narrative review: continuous glucose monitoring (CGM) in older adults with diabetes. Diabetes Ther. 2025;16(6):1139-1154. doi: 10.1007/s13300-025-01720-z [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Uhl S, Choure A, Rouse B, Loblack A, Reaven P. Effectiveness of continuous glucose monitoring on metrics of glycemic control in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. J Clin Endocrinol Metab. 2024;109(4):1119-1131. doi: 10.1210/clinem/dgad652 [DOI] [PubMed] [Google Scholar]
- 4.Jancev M, Vissers TACM, Visseren FLJ, et al. Continuous glucose monitoring in adults with type 2 diabetes: a systematic review and meta-analysis. Diabetologia. 2024;67(5):798-810. doi: 10.1007/s00125-024-06107-6 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Alfadli SF, Alotaibi YS, Aqdi MJ, et al. Effectiveness of continuous glucose monitoring systems on glycemic control in adults with type 1 diabetes: a systematic review and meta-analysis. Metabol Open. 2025;27:100382. doi: 10.1016/j.metop.2025.100382 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Kim JY, Kim S, Kim JH. Comparison of real-time and intermittently-scanned continuous glucose monitoring for glycemic control in type 1 diabetes mellitus: nationwide cohort study. Diabetes Metab J. 2025;49(3):436-447. doi: 10.4093/dmj.2024.0160 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Lin YK, Groat D, Chan O, et al. Alarm settings of continuous glucose monitoring systems and associations to glucose outcomes in type 1 diabetes. J Endocr Soc. 2019;4(1):bvz005. doi: 10.1210/jendso/bvz005 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Welsh JB, Gao P, Derdzinski M, et al. Accuracy, utilization, and effectiveness comparisons of different continuous glucose monitoring systems. Diabetes Technol Ther. 2019;21(3):128-132. doi: 10.1089/dia.2018.0374 [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eMethods
Data Sharing Statement
