Hemoglobin A1c Accurately Predicts Continuous Glucose Monitoring-Derived Average Glucose in Youth and Young Adults With Cystic Fibrosis

Diabetes Care. 2018 Jul;41(7):1406-1413. doi: 10.2337/dc17-2419. Epub 2018 Apr 19.

Abstract

Objective: In cystic fibrosis (CF), hemoglobin A1c (HbA1c) is thought to underestimate glycemia. However, few studies have directly assessed the relationship between HbA1c and average glucose in CF. We determined the relationships among glycemic markers-HbA1c, fructosamine (FA), glycated albumin (%GA), and 1,5-anhydroglucitol (1,5-AG)-and continuous glucose monitoring (CGM) in CF, hypothesizing that alternate markers would better predict average sensor glucose (ASG) than HbA1c.

Research design and methods: CF participants and a group of healthy control subjects (HCs), ages 6-25 years, wore CGM for up to 7 days. Pearson correlations assessed the relationships between CGM variables and HbA1c, FA, %GA, and 1,5-AG. The regression line between HbA1c and ASG was compared in CF versus HC. Linear regressions determined whether alternate markers predicted ASG after adjustment for HbA1c.

Results: CF (n = 93) and HC (n = 29) groups wore CGM for 5.2 ± 1 days. CF participants were 14 ± 3 years of age and 47% were male, with a BMI z score -0.1 ± 0.8 and no different from HCs in age, sex, or BMI. Mean HbA1c in CF was 5.7 ± 0.8% (39 ± 9 mmol/mol) vs. HC 5.1 ± 0.2% (32 ± 2 mmol/mol) (P < 0.0001). All glycemic markers correlated with ASG (P ≤ 0.01): HbA1c (r = 0.86), FA (r = 0.69), %GA (r = 0.83), and 1,5-AG (r = -0.26). The regression line between ASG and HbA1c did not differ in CF versus HC (P = 0.44). After adjustment for HbA1c, %GA continued to predict ASG (P = 0.0009) in CF.

Conclusions: HbA1c does not underestimate ASG in CF as previously assumed. No alternate glycemic marker correlated more strongly with ASG than HbA1c. %GA shows strong correlation with ASG and added to the prediction of ASG beyond HbA1c. However, we are not advocating use of HbA1c for diabetes screening in CF based on these results. Further study will determine whether glycemic measures other than ASG differ among different types of diabetes for a given HbA1c.

Trial registration: ClinicalTrials.gov NCT02211235.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Biomarkers / analysis
  • Biomarkers / blood*
  • Blood Glucose / metabolism*
  • Blood Glucose Self-Monitoring / instrumentation
  • Blood Glucose Self-Monitoring / methods
  • Case-Control Studies
  • Child
  • Cystic Fibrosis / blood*
  • Cystic Fibrosis / complications
  • Cystic Fibrosis / diagnosis
  • Diabetes Mellitus / blood
  • Diabetes Mellitus / diagnosis*
  • Female
  • Fructosamine / blood
  • Glycated Hemoglobin / analysis*
  • Glycated Serum Albumin
  • Glycation End Products, Advanced
  • Humans
  • Male
  • Mass Screening* / instrumentation
  • Mass Screening* / methods
  • Predictive Value of Tests
  • Reproducibility of Results
  • Serum Albumin / analysis
  • Young Adult

Substances

  • Biomarkers
  • Blood Glucose
  • Glycated Hemoglobin A
  • Glycation End Products, Advanced
  • Serum Albumin
  • Fructosamine
  • Glycated Serum Albumin

Associated data

  • ClinicalTrials.gov/NCT02211235