The relationship between glycated haemoglobin levels and the risk of giant cell arteritis - a case-control study

Chetan Mukhtyar; Holly Myers; Colin Jones; Ketan Dhatariya

doi:10.1093/rap/rkaa018

The relationship between glycated haemoglobin levels and the risk of giant cell arteritis - a case-control study

Rheumatol Adv Pract. 2020 May 28;4(2):rkaa018. doi: 10.1093/rap/rkaa018. eCollection 2020.

Authors

Chetan Mukhtyar^{1

2}, Holly Myers^{1

2}, Colin Jones³, Ketan Dhatariya^{2

4}

Affiliations

¹ Department of Rheumatology, Norfolk and Norwich University Hospital NHS Foundation Trust.
² Norwich Medical School, University of East Anglia.
³ Department of Ophthalmology, Norfolk and Norwich University Hospital NHS Foundation Trust.
⁴ Elsie Bertram Diabetes Centre, Norfolk and Norwich University Hospital NHS Foundation Trust, Norwich, UK.

Abstract

Objectives: The EULAR core dataset for observational studies in GCA does not include glycated haemoglobin (HbA_1c). A multivariable score to stratify the pre-test probability of GCA also does not include HbA_1c. There have been contradictory reports about diabetes mellitus being a risk factor for GCA. We report the first study analysing the relationship of pre-diagnosis HbA_1c with the risk of GCA.

Methods: This was a single-centre retrospective case-control study conducted in Norfolk, UK. All GCA cases were diagnosed with imaging or biopsy. Each case was assigned two age- and sex-matched controls. The primary outcome measure was the glycaemic status (HbA_1c categorized into euglycaemia, pre-diabetes or diabetes mellitus) at diagnosis between cases and controls. The HbA_1c was compared between two groups using the Mann-Whitney U test. The glycaemic categorization was compared using the χ² test.

Results: One hundred and twelve cases and 224 controls were included. The median (interquartile range) of HbA_1c of cases and controls was 40 (37, 43) and 41 (39, 47) mmol/mol (P < 0.001), respectively. Ten of 112 cases and 52 of 224 controls had diabetes mellitus. The χ² test demonstrated a significant interaction between glycaemic state and GCA (P = 0.006). Individuals with diabetes mellitus had an odds ratio (95% CI) of 0.32 (0.13, 0.74) (P = 0.008) of having GCA compared with euglycaemic individuals.

Conclusion: HbA_1c in the diabetic range reduces the probability of GCA. HbA_1c should be considered in any multivariable score to calculate the risk of GCA, and in future development of diagnostic and classification criteria. There is a need for an epidemiological study looking at the possibility of a protective nature of diabetes mellitus against GCA or whether it is only a mimic.

Keywords: case–control study; diabetes mellitus; giant cell arteritis; glycated haemoglobin; risk stratification.