Abstract
Background:
Continuous glucose monitoring (CGM) measures glucose levels every 1 to 15 minutes and is widely used in clinical and research contexts. Statistical packages and algorithms reduce the time-consuming and error-prone process of manually calculating CGM metrics and contribute to standardizing CGM metrics defined by international consensus. The aim of this systematic review is to summarize existing data on (1) statistical packages for retrospective CGM data analysis and (2) statistical algorithms for retrospective CGM analysis not available in these statistical packages.
Methods:
A systematic literature search in PubMed and EMBASE was conducted on September 19, 2023. We also searched Google Scholar and Google Search until October 12, 2023 as sources of gray literature and performed reference checks of the included literature. Articles in English and Danish were included. This systematic review is registered with PROSPERO (CRD42022378163).
Results:
A total of 8731 references were screened and 46 references were included. We identified 23 statistical packages for the analysis of CGM data. The statistical packages could calculate many metrics of the 2022 CGM consensus and non-consensus CGM metrics, and 22/23 (96%) statistical packages were freely available. Also, 23 statistical algorithms were identified. The statistical algorithms could be divided into three groups based on content: (1) CGM data reduction (eg, clustering of CGM data), (2) composite CGM outcomes, and (3) other CGM metrics.
Conclusion:
This systematic review provides detailed tabular and textual up-to-date descriptions of the contents of statistical packages and statistical algorithms for retrospective analysis of CGM data.
Keywords
Introduction
Continuous glucose monitoring (CGM) is an established technology in research and clinical practice.1,2 Continuous glucose monitoring provides information on glucose levels collected automatically every 1 to 15 minutes.
Consensus on reporting CGM outcomes is established. 3 However, handling large amounts of CGM data is challenging. The manual entering of summary statistics from the ambulatory glucose profile (AGP) reports from CGM manufacturers into databases before analysis is time-consuming and prone to error, although AGP report summary statistics are often used in clinical studies.4,5 Continuous glucose monitoring manufacturers use different algorithms to compute CGM summary statistics and graphical displays of the glycemic status in AGP reports. 6 Consequently, comparison of AGP reports between CGM manufacturers can be challenging. Also, specific research questions or clinical situations might require different summary statistics not offered by AGP reports from CGM manufacturers, for example, different glycemic variability metrics 7 or different hypoglycemic and hyperglycemic cut-offs. 8
A recent review of 12 statistical packages has been published. 9 However, no systematic review of statistical packages and statistical algorithms for retrospective analysis of CGM data exists. The objective of the present review is to summarize existing data on (1) statistical packages to retrospectively analyze CGM data and (2) statistical algorithms for retrospective CGM data analysis not currently available in these statistical packages. The present review has the potential to contribute to the standardization of CGM reporting 3 or, where appropriate, to contribute to more individualized statistical approaches in CGM analysis useful to researchers and clinicians in need of tools capable of analyzing CGM data retrospectively.
Methods and Materials
A systematic literature search was performed on September 19, 2023 (no lower publication date limit) in PubMed and Embase (Figure 1). We also searched Google Scholar and Google Search until October 12, 2023 as important sources of gray literature and performed reference checks of the included literature. An information specialist assisted in defining the search strings, see Supplementary Material. Important search words include: (“statistics” OR “analysis” OR “algorithm” OR “tools” OR “software”) AND (“continuous glucose monitoring” OR “CGM”). The titles and abstracts were screened for eligibility by reviewer 1 (MTO) and reviewer 2 (CKK) in Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). Disagreements were resolved by discussion or by consulting reviewer 3 (PLK). This systematic review is registered with PROSPERO (CRD42022378163) and follows the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 guideline. 10

PRISMA diagram.
Eligibility Criteria
Inclusion criteria: Statistical packages and/or statistical algorithms for retrospective analysis of CGM data.
Exclusion criteria: Statistical packages and/or statistical algorithms for glucose level predictions or statistical algorithms relying on an artificial pancreas setup. Statistical packages and/or statistical algorithms for denoising (ie, “smoothing”) of CGM traces, sensor drift, interstitial-to-plasma glucose time delay, and calibration of CGM signals.
Data Extraction and Presentation
Results on statistical packages (Tables 1 and 2) and statistical algorithms (Table 3) were tabulated. The corresponding authors were contacted for missing information.
Information on Statistical Packages for Retrospective Analysis of Continuous Glucose Monitoring Data.
Table 1 provides an overview of the statistical packages with (A) authors of the statistical packages and publication year, (B) a summary of the statistical package content and previous package versions, (C) graphical user interphase (yes/no), (D) the data structure required when uploading CGM data for package analysis, (E) possibility of exporting/downloading results from the package analysis (yes/no), (F) open-source code (yes/no), and (G) publicly available (yes/no).
Abbreviations: AGATA, automated glucose dATa analysis; AUC, area under curve; CGDA, continuous glucose data analysis; CGM-GUIDE, continuous glucose monitoring graphical user interface with diabetes evaluation; CGMTSA, continuous glucose monitoring time series data analysis; CONGA, continuous overall net glycemic action; CV, coefficient of variation; EF, excursion frequency; GMI, glucose management indicator; GRADE, glycemic risk assessment diabetes equation; GVAP, glycemic variability analyzer program; iglu, interpreting blood GLUcose; KAMOGAWA, Kyoto Auto MAGE Of Glucose cAlculator With isCGM Application; MAD, median absolute deviation; MAGE, mean amplitude of glycemic excursions; MODD, mean of daily differences; NA, not available; SD, standard deviation; sGVP: standardized glycemic variability percentage; TAR, time above range; TBR, time below range; TIR, time in range.
Consensus Metrics, 3 Additional Metrics, Imputation Options, and Multiple Group Comparison Options for Statistical Packages for Retrospective Analysis of Continuous Glucose Monitoring Data.
Abbreviations: AGATA, Automated Glucose dATa Analysis; CGDA, continuous glucose data analysis; CGM-GUIDE, continuous glucose monitoring graphical user interface with diabetes evaluation; CGMTSA, continuous glucose monitoring time series data analysis; GVAP, glycemic variability analyzer program; iglu, interpreting blood GLUcose; KAMOGAWA, Kyoto Auto MAGE Of Glucose cAlculator With isCGM Application; NA, not available.
Times in different ranges are not directly provided. For the GVAP package, 22 percentages above and below a customizable target range are computed. For the CGMStatsAnalyser 68 and CGM Shiny packages, TBR < 3.9 mmol/L or < 70 mg/dL is the sum of TBR level 1 and TBR level 2, and TAR > 10.0 mmol/L or > 180 mg/dL is the sum of TAR level 1 and TAR level 2.
Several subtypes of AUC calculations are possible in the CGDA package, 67 for example, AUC average per day. The packages CGM-GUIDE, 32 GVAP, 22 CGMStatsAnalyser, 68 and AGATA 16 have customizable lower and upper glycemic limits for AUC calculation.
Sum of the absolute difference in glucose levels from successive CGM measurements over a given interval of time.
The GVAP 22 package counts excursions (n) above a customizable glycemic amplitude. The packages cgmanalysis 17 and CGDA 67 count excursions (n) in customizable ranges of glucose levels with customizable thresholds for the number of minutes an excursion has to persist to be counted.
GLU package 60 gives a measure of fasting glucose levels without the knowledge of mealtimes. Calculation is based on the mean of the lowest glucose levels in 30 consecutive minutes during the night time.
The packages Easy GV, 33 iglu, 15 rGV, 61 and AGATA 16 provide computation of the relative contribution of hypoglycemia, euglycemia, and hyperglycemia to the GRADE score.
Interquartile ranges are not directly provided but can be calculated from subtracting the first quartile from the second quartile.
Separates MAGE into MAGE for upward and downward glucose excursions.
Includes glucose rise to peak (ie, difference in glucose levels before meal till glucose peak during the meal), time to peak (ie, difference in time before meal till glucose peak during meal), and % baseline recovery one hour after glucose level peak.
Mean of sensor glucose levels in- and outside range with default settings of 1 SD of mean sensor glucose as inside range.
Several subtypes of within and between days SD calculations are offered in Rodbard 28 and SD of within-day mean index and mean of within-day SD index in AGATA. 16
Combination of CGM traces from different days and/or different subjects and combines them in one plot with median and percentiles displayed as a single day as known from the AGP report. 6 AGATA package 16 also plots CGM traces over multiple days with superimposed aggregated glucose values to facilitate the identification of meaningful hyperglycemic and hypoglycemic events.
Plot the mean and standard error or standard deviation of multiscale entropy by groups.
Frequency of glucose transitions per day as they move between critical glycemic zones.
Statistical Algorithms for Retrospective Analysis of Continuous Glucose Monitoring Data Not Included in Any Statistical Packages.
Table 3 provides information on the statistical algorithms with (A) authors of the statistical algorithm and publication year, (B) summary of content, (C) core statistical methods used to develop the algorithm, (D) testing of the algorithm in (n) subjects and on (n) CGM days, and (E) CGM type(s) used to illustrate the algorithm.
Abbreviations: AUC, area under curve; CGM, continuous glucose monitoring; CGP, comprehensive glucose pentagon; CONGA, continuous overall net glycemic action; CPGV, consensus perceived glycemic variability; CV, control variability; GCI, glycemic deviation index; HBGI, high blood glucose index; LBGI, low blood glucose index; MAGE, mean amplitude of glycemic excursions; MODD, mean of daily differences; NA, not available; T1DM, type 1 diabetes mellitus; T2DM, type 2 diabetes mellitus; TAR, time above range; TBR, time below range; TIR, time in range.
Results
Statistical Packages
We identified 23 statistical packages (Table 1) and have tabulated the computable CGM metrics (Table 2). The packages can compute the metrics listed in Table 2 regardless of glucose reporting frequency specific for the CGM device, often every 1, 5, or 15 minutes. In total, 14 (61%) of the packages had a graphical user interface, input formats were .csv, .txt, .mat, .xls, or .xlsx and glucose level units were in mmol/L and mg/dL (manual conversions are possible between formats and units). Furthermore, 20 (87%) of the statistical packages could export/download results, 16 (70%) were open source, 22 (96%) were publicly available, 11 (48%) could impute missing CGM data, and five (24%) could perform multiple group comparisons.
Statistical Algorithms Not Included in Statistical Packages
We identified 23 statistical algorithms not included in any statistical packages but still relevant for retrospective analysis of CGM data (Table 3). The statistical algorithms are grouped by: (1) CGM data reduction (eg, clustering of CGM data), (2) composite CGM outcomes, and (3) other CGM metrics.
In total, 19 (83%) of the statistical algorithms were illustrated with use of CGM data in the original articles. The remaining four (17%) of the statistical algorithms by Kovatchev et al, 11 Rodbard, 12 Rodbard, 13 and Vigersky 14 are conceptual and independent of specific CGM types and/or patient characteristics and not illustrated with use of CGM data.
Discussion
Statistical Packages
Usability and compatibility
This systematic review identified 23 statistical packages for the retrospective analysis of CGM data (Table 1). The packages iglu, 15 AGATA, 16 and cgmanalysis 17 could calculate the most CGM metrics (n = 47, n = 37, and n = 31, respectively) and also the most of the 2022 CGM consensus metrics (n = 16, n = 16, and n = 15, respectively) (Table 2) which makes these packages highly usable. The iglu 15 and AGATA 16 packages were the only ones to calculate glycemia risk index (GRI). 18 None of the statistical packages could estimate the scanning frequency (for flash glucose monitoring) nor the several secondary endpoints (binary outcomes) or composite endpoints of the 2022 CGM consensus. 3
GlyCulator 3.0 19 and Tidepool Platform 20 provide a graphical user interface and video tutorial on how to use them and may be preferable for basic researchers not skilled in, for example, RStudio. Tidepool also has the advantage that patients can share access to glucose data with their health care professionals or relatives (including data from insulin pumps, blood glucose meters, and ketone monitors) and can therefore be used for telemedicine. The packages AGATA, 16 MAGECAA, 21 and GVAP 22 require MATLAB to run, which might limit the usability of those solutions. The additional statistical packages (Table 1) run in RStudio, in Excel, or as interactive web Shiny apps.
Imputation of missing data
When working with CGM data, censored and missing data frequently occur. 23 At least, 70% of data availability over 14 days is recommended.3,24 Recently, a greater awareness of missing data in research has emerged.25-27 Currently, no consensus exists on how to manage missing CGM data. 23 In the present review, 11 (48%) of the statistical packages could impute missing data (Table 2), including the previous mentioned packages iglu, 15 AGATA, 16 and cgmanalysis. 17
Glycemic variability
A strong focus on assessing glycemic variability more precisely with CGM than is possible by POC (point-of-care) glucose data are reflected in the first statistical packages released by Rodbard, 28 Baghurst, 29 Fritzsche et al, 30 Hill et al, 31 and Rawlings et al 32 (Table 1). Interestingly, the top 3 cited packages according to Google per year, Rodbard 28 (average of 17.3 citations yearly), EasyGV 33 (average of 34.0 citations yearly), and Hall et al 34 (average of 37.6 citations yearly), all focus on calculating glycemic variability.
Glycemic variability was conceptually introduced many years before CGM as evidenced by the mean amplitude of glycemic excursions (MAGE) in 1970, 35 the mean of daily differences (MODD) in 1972, 36 and the J-index in 1995. 37 Today, the most popular metric for reporting glycemic variability is the coefficient of variation (CV). It has been recommended that CV is less than or equal to 36% for patients with type 1 diabetes. 3 Several other metrics of glycemic variability are also validated and are implemented in statistical packages (Table 2). Nearly, all glycemic variability metrics are highly correlated with standard deviation (SD) of glucose distribution.38-40 Recent reviews have been published on the clinical implications of glycemic variability in diabetes.41-47
Graphical display options
Continuous glucose monitoring summary statistics do not, in general, consider that CGM data are time series data. 48 For example, consider CGM glucose data ordered in time from 3.0 to 3.5 to 4.0 mmol/L (54-63-72 mg/dL) and from 4.0 to 3.5 to 3.0 mmol/L (72-63-54 mg/dL). These glucose sequences are clinically very different situations regarding hypoglycemia but yield identical summary statistics, for example, mean glucose level and CV. The example demonstrates the need for clinical judgment and visual interpretation of CGM data.49-52 The statistical packages iglu 15 and AGATA 16 provide the most graphical display options (Table 2) alongside summary statistics.
Standardization vs customization
The AGP4,53 is the basis for the first consensus on CGM metrics and visualization released in 2012 by the International Diabetes Center. 38 The AGP report has three major components: (1) glucose statistics and time in different glucose ranges, (2) a single 24-hour “modal” day that combines all daily CGM glucose data, referred to as AGP, and (3) daily glucose profiles. 6 Commercial tools for retrospective analysis and visualization of CGM data are based on AGP principles (eg, Glooko, 54 Dexcom Clarity, 55 Eversense Data Management System, 56 Medtronic Carelink, 57 and Abbot LibreView 58 ). These commercial solutions compute only a subset of CGM metrics, often time in different glucose ranges, CV, mean glucose levels, and glucose management indicator (GMI). While simple, standardized overviews of CGM data are often useful in clinical practice, researchers often need different metrics and graphical display options of CGM data to answer specific research questions and/or to align with the 2022 CGM consensus. 3 Standardization must be done in a manner that permits diversity of clinical situations and fosters research innovations. 59
Both the statistical packages (Tables 1 and 2) and the statistical algorithms (Table 3) can complement the standardized AGP report and generate information not currently provided in the AGP report, for example, possible changes in glycemic target ranges more suitable for the patients prone to hypoglycemia, elderly patients or during pregnancy. Customizable thresholds for time in different ranges are possible to compute by the packages: EasyGV, 33 CGM-GUIDE, 32 GVAP, 22 Tidepool 20 cgmanalysis, 17 GLU, 60 iglu, 15 rGV, 61 and GlyCulator 3.0. 19
It has been proposed 62 that the AGP report should also include (1) hypoglycemic and hyperglycemic events (which is possible by the packages iglu 15 and AGATA 16 ), (2) details on postprandial excursions (which is possible by packages GLU 60 and iglu 15 ), (3) account for the skewed distribution of CGM data (which is possible by several of the statistical packages (Table 2) by blood glucose risk index [BGRI], 11 low blood glucose index [LBGI],63,64 and high blood glucose index [HBGI] 64 ), and (4) provide methods to compare CGM metrics between groups or individuals, which is possible by the statistical packages16,65-68 (Table 1).
Statistical Algorithms
This systematic review identified 23 statistical algorithms (Table 3) for the retrospective analysis of CGM data but not included in any of the 23 statistical packages (Tables 1 and 2).
CGM data reduction
The purpose of most of the reviewed algorithms is to cluster data. Subgroups or “clusters” of patients with diabetes might foster precision medicine initiatives aiming to characterize homogeneous subgroups based on the individuals’ characteristics.69-71 In time, this could lead to the development of targeted interventions for disease prevention.72,73 Recently, data-driven analytical methods have identified distinctive subgroups of individuals with type 2 diabetes or prediabetes and their associations with diabetes complications.74-76 A barrier to implementing some of the statistical algorithms in daily clinical practice is that the clustering algorithms reviewed here77-82 might require initial training on data in similar setups used by their developers. Therefore, the algorithms are probably primarily useful in research.
Composite CGM outcomes
Several composite CGM metrics have been proposed (Table 3). There are clinical advantages to composite metrics. 83 Composite metrics giving weight to hypoglycemia and hyperglycemia 84 might be an advantage since some of the widely used CGM metrics, for example, CV, time in range (TIR), and mean glucose level, are more correlated with hyperglycemia due to the skewed glucose level distribution.84-88 Algorithms accounting for skewed glucose distributions have been developed, for example, BGRI, 11 LBGI,63,64 HBGI, 64 index of glycemic control (IGC), 40 and glycemic risk assessment diabetes equation (GRADE). 89 However, these metrics are often neglected, possibly due to the difficulty of computing them 61 and/or interpreting them. 84 Today, several statistical packages offer easy calculations of these metrics (Table 2). The statistical algorithms by Thomas et al 90 and Vigersky 14 include HbA1c as one component in the composite metric and are not exclusively CGM-based. Reviews on CGM-based composite metrics have been published.88,91 Recently, the composite metric GRI 18 has been included in the 2022 CGM consensus. 3
Other CGM metrics
The additional CGM metrics identified (Table 3) all focus on glycemic variability. Interestingly, the metrics developed by Marling et al92,93 are based on clinicians’ perceived risk regarding glycemic variability from CGM glucose traces and not based on more traditional analytical data approaches as cluster analyses or constructing composite metrics from already established glycemic metrics as reviewed above. More established CGM metrics also taking advantage of such perceived risks include the GRADE score, 94 the Q-score, 95 the IGC, 40 and the GRI, 18 all based on a clinical perception of the risk of adverse outcomes associated with a glucose profile. 89 In relation to the GRADE score, the perceived risk differs from health care professionals and patients. 94 These metrics are developed to capture what clinicians perceive and treat as dangerous glucose levels and might supplement more traditional ways of interpreting CGM data.
A gold standard metric or algorithm
Recent work has been performed to identify gold standard metrics and algorithms to optimize the use of CGM data by the discriminant ratio. 96 The discriminant ratio is a way to compare different metrics to determine the ability of each metric to discriminate between different people with diabetes. Mean absolute glucose (MAG), LBGI, and TIR have the highest discriminant ratio in the tested metrics. 96 However, more research is needed to establish correlations between these metrics and short-term and long-term diabetes complications. Therefore, clinicians and researchers continue to balance between not having too many CGM metrics that they become confusing 97 and still having enough metrics to match the sophistication of CGM technology.
Conclusion
This systematic review identified 23 statistical packages (Table 1) for retrospective analysis of CGM data with textual and tabular (Table 2) overviews of computable CGM metrics, plots, and graphs in the statistical packages and whether imputation of missing CGM data is possible. An additional 23 statistical algorithms were identified (Table 3) that are relevant for retrospective analysis of CGM data not included in the statistical packages. The statistical packages and algorithms supplement CGM manufacturers’ CGM reports with additional CGM metrics, plots, and graphs according to specific research questions or clinical situations.
Future Perspectives
Statistical methods to handle censored CGM data are needed. Options for group comparisons and graphical user phase solutions for non-programmers should be expanded since only five (22%) and 14 (61%) of the statistical packages have these options, respectively.
Supplemental Material
sj-docx-1-dst-10.1177_19322968231221803 – Supplemental material for Statistical Packages and Algorithms for the Analysis of Continuous Glucose Monitoring Data: A Systematic Review
Supplemental material, sj-docx-1-dst-10.1177_19322968231221803 for Statistical Packages and Algorithms for the Analysis of Continuous Glucose Monitoring Data: A Systematic Review by Mikkel Thor Olsen, Carina Kirstine Klarskov, Arnold Matovu Dungu, Katrine Bagge Hansen, Ulrik Pedersen-Bjergaard and Peter Lommer Kristensen in Journal of Diabetes Science and Technology
Footnotes
Acknowledgements
The authors are grateful for the advice on the search strings by information specialist Jette Melby at Copenhagen University Hospital—North Zealand, Denmark.
Abbreviations
AGP, ambulatory glucose profile; BGRI, blood glucose risk index; CGM, continuous glucose monitoring; GMI, glucose management indicator; GRADE, glycemic risk assessment diabetes equation; GRI, glycemia risk index; HbA1c, hemoglobin a1c; HBGI, high blood glucose index; IGC, index of glycemic control; LBGI, low blood glucose index; MAG, mean absolute glucose; SD, standard deviation; TIR, time in range.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The Novo Nordisk Foundation (grant no. NNF20SA0062872).
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References
Supplementary Material
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