Validation of Hemoglobin A1c in Patients With Inflammatory Arthritis Treated With Sulfasalazine (DIA2SULFA)

February 10, 2026 updated by: Klavs Würgler Hansen

How Can We Prevent the Underdiagnosis of Diabetes and the Undertreatment of Known Diabetes in Patients With Inflammatory Arthritis Treated With Sulfasalazine?

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)?

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Detailed Description

HbA1c is widely used to diagnose diabetes and to monitor long-term glycaemic control. HbA1c reflects average blood glucose levels over approximately two months but can be influenced by factors unrelated to glucose, including changes in red blood cell lifespan. Sulfasalazine, a disease-modifying antirheumatic drug commonly used to treat inflammatory arthritis, is known to cause mild haemolysis in some patients, which can lower HbA1c values independently of actual glucose levels.

This effect may have important clinical consequences. In patients without diabetes at the start of sulfasalazine treatment, HbA1c values may remain below diagnostic thresholds even if diabetes develops over time, potentially delaying diagnosis. In patients with established diabetes, sulfasalazine-associated lowering of HbA1c may give a misleading impression of adequate glycaemic control, which may result in insufficient treatment intensification despite elevated true glucose levels. Together, these mechanisms may contribute to underdiagnosis and undertreatment of diabetes in patients receiving sulfasalazine.

CGM provides direct, sensor-based measurements of interstitial glucose levels and is not affected by red blood cell turnover. CGM therefore offers an opportunity to assess actual glycaemic exposure independently of HbA1c. However, prospective data comparing HbA1c with CGM-derived glucose measures in sulfasalazine-treated patients with inflammatory arthritis are lacking.

This study is a prospective observational investigation conducted in patients with inflammatory arthritis treated with sulfasalazine. Participants include both individuals with known diabetes and individuals without known diabetes who have HbA1c values in the borderline range. Each participant undergoes a single study phase in which blinded CGM is worn for up to 14 days, with blood sampling performed within the same time period. In participants without known diabetes, fasting plasma glucose measurements are used to evaluate the presence of previously unrecognised diabetes.

By comparing HbA1c values with CGM-derived average glucose levels, the study aims to evaluate whether HbA1c accurately reflects glycaemic status in sulfasalazine-treated patients. The results are expected to improve understanding of the limitations of HbA1c in this clinical context and to inform future strategies for diabetes diagnosis and monitoring in patients receiving sulfasalazine, including the potential need for alternative or supplementary glucose assessment methods.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Observational

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
75

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.
  • Name: Katrine B Gørlitz, MD
  • Phone Number: 0045 2421 0787
  • Email: kagoer@rm.dk

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

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.

Description

Inclusion Criteria:

  • 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))
  • Can communicate in Danish
  • Informed consent including permission to upload glucose data and study ID to the Libreview Platform.

Exclusion Criteria:

  • 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.)

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort

Group / Cohort

A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.
Inflammatory arthritis with borderline HbA1c

This cohort includes adults with inflammatory arthritis treated with sulfasalazine who do not have a prior diagnosis of diabetes mellitus and have a borderline HbA1c value (≥38 mmol/mol) measured at least two months after initiation of sulfasalazine.

Participants undergo blinded continuous glucose monitoring for up to 14 days to assess actual glucose levels. At the end of the monitoring period, blood samples are obtained for fasting plasma glucose and HbA1c.

Fasting plasma glucose and HbA1c are used to assess the presence of diabetes mellitus, and thereby whether HbA1c and is suitable for the diagnosis of diabetes in patients treated with sulfasalazine. Comparison of HbA1c with CGM-derived glucose measures allows evaluation of whether HbA1c accurately reflects true glycaemic status in patients treated with sulfasalazine.
Inflammatory arthritis with diabetes

This cohort includes adults with inflammatory arthritis and a known diagnosis of diabetes mellitus who are treated with sulfasalazine.

Participants undergo blinded continuous glucose monitoring for up to 14 days to assess average glucose levels. HbA1c is measured during the same period. Comparison of HbA1c with CGM-derived glucose measures allows evaluation of whether HbA1c accurately reflects glycaemic control in patients with established diabetes receiving sulfasalazine.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Prevalence of undiagnosed diabetes mellitus
Time Frame: Within 14-21 days
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.
Within 14-21 days

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Agreement between HbA1c and CGM-derived mean glucose in sulfasalazine-treated patients
Time Frame: Within 14-21 days
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.
Within 14-21 days

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Feasibility of automated laboratory-based HbA1c alert in sulfasalazine-treated patients
Time Frame: Approximately 9 months
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.
Approximately 9 months

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Klavs Würgler Hansen

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Principal Investigator: Klavs W Hansen, Clinical Professor, Medicial Diagnostic Center, Silkeborg Regional Hospital

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
February 1, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
June 1, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
September 1, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
February 10, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 10, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
February 18, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
February 18, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 10, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
February 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 1-10-72-190-25

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

UNDECIDED

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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