[Use of rheumatoid factor IgM analysis. A questionnaire study among the users]

Area of Science:

• Clinical Chemistry
• Immunology
• Rheumatology

Background:

• Rheumatoid factor (RF-IgM) is an antibody associated with autoimmune diseases, particularly rheumatoid arthritis.
• Understanding the utilization patterns and clinical indications for RF-IgM testing is crucial for appropriate diagnostic strategies.

Purpose of the Study:

• To investigate the demographic and clinical characteristics of patients undergoing RF-IgM analysis.
• To compare the ordering patterns and clinical indications with the laboratory results of RF-IgM tests.
• To assess the impact of different cut-off values on the interpretation of RF-IgM results.

Main Methods:

• A retrospective analysis of all RF-IgM tests performed over a one-month period.
• Physician questionnaires to gather data on clinical symptoms, other laboratory results, and testing history.
• Analysis of positive ELISA results based on a standard cut-off of 6 IU/ml.

Main Results:

• 467 RF-IgM analyses were registered in a population of approximately 300,000.
• 21% of analyses yielded a positive RF-IgM result (cut-off: 6 IU/ml).
• Only 31% of patients presented with clinical symptoms suggestive of rheumatoid arthritis.
• 67% of tests were ordered by general practitioners, indicating significant use in case-finding.
• Altering the cut-off to 15 or 20 IU/ml drastically reduced positive results to 14 or 12, respectively.

Conclusions:

• The RF-IgM assay is often employed for broad case-finding, potentially leading to overuse.
• More specific utilization of RF-IgM testing could help reduce its frequency.
• Clinicians receiving RF-IgM results must be aware of the significant impact of the laboratory's chosen cut-off value on test interpretation.