The purpose of this study is to examine whether the blood test Hemoglobin A1c (HbA1c) gives an accurate picture of blood glucose levels in patients with inflammatory arthritis who are treated with sulfasalazine. HbA1c is widely used to diagnose and monitor diabetes, but sulfasalazine can shorten red blood cell lifespan and thereby lower HbA1c values independently of actual glucose levels.
This may lead to underdiagnosis of diabetes in patients who develop diabetes during sulfasalazine treatment, and to undertreatment in patients with known diabetes due to falsely reassuring HbA1c values.
The study aims to answer two main questions:
1. How many patients treated with sulfasalazine have undiagnosed diabetes despite having HbA1c values below the diagnostic threshold? 2. Does HbA1c underestimate actual glucose levels when compared with continuous glucose monitoring (CGM) in patients with sulfasalazine-treated inflammatory arthritis, both in those with known diabetes and those that are not diagnosed with diabetes but have borderline HbA1c values (≥ 38 mmol/mol)?
Age ≥18 years
Treatment with sulfasalazine for at least 2 months prior to inclusion
Inflammatory arthritis diagnosis (Reumatoid Arthritis, Reaktive Arthritis, Axial spa, Psoriatic spondylitis, and Juvenil artrit)
HbA1c ≥38 mmol/mol obtained at least 2 months after sulfasalazine initiation OR a diabetes mellitus diagnosis (Type 1 diabetes mellitus, Type 2 diabetes mellitus, Malnutrition-related diabetes mellitus, Other specified diabetes mellitus (andre specificerede former for diabetes), and Unspecified diabetes mellitus (uspecificeret diabetes))
Systemic treatment or local injections with glucocorticoids within the previous 2 months or planned within the following 4 weeks
Clinical conditions interfering with the interpretation of HbA1c expect for sulfasalazine alterations in red cell lifespan (etc. Dapson treatment)
Allergy towards the adhesive used in the CGM
Considered ineligible for participating (e.g. patients without decision-making capacity, , malignancy, terminal illness, ect.)
Patients will be recruited from the rheumatology outpatient clinic at the Medicial Diagnostic Center, Silkeborg Regional Hospital. Potential participants will be identified electronically using registry data. Scrutiny of their electronical medical records will be performed to confirm eligibility based on the above mentioned inclusion and exclusion criteria.
Cohort
Prospective
Not listed
Prevalence of undiagnosed diabetes mellitus
The primary outcome is the prevalence of previously undiagnosed diabetes mellitus among adults with inflammatory arthritis treated with sulfasalazine who do not have a known diagnosis of diabetes and have a borderline HbA1c value. Undiagnosed diabetes is defined based on fasting plasma glucose measurements obtained during the study, in accordance with established diagnostic criteria. The prevalence is expressed as the proportion of participants meeting the diagnostic criteria for diabetes mellitus.
Agreement between HbA1c and CGM-derived mean glucose in sulfasalazine-treated patients
The secondary outcome is the agreement between HbA1c and average glucose levels measured by blinded CGM in adults with inflammatory arthritis treated with sulfasalazine. Mean glucose derived from CGM over the monitoring period is compared with contemporaneous HbA1c values to evaluate whether HbA1c accurately reflects true glycaemic status in this population. The analysis includes participants with known diabetes mellitus and participants without known diabetes but with borderline HbA1c values.
Feasibility of automated laboratory-based HbA1c alert in sulfasalazine-treated patients
This outcome assesses the feasibility of implementing an automated laboratory-based alert in the laboratory information system (LABKA) to flag potential interpretive limitations of HbA1c in patients treated with sulfasalazine. Feasibility is evaluated by determining whether HbA1c test results can be systematically linked to active sulfasalazine treatment and whether an automated notification can be generated to inform clinicians that HbA1c may underestimate true glycaemic status in this context.
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Klavs Würgler Hansen
Lead sponsor
Central Jutland Regional Hospital
Sponsor institution
