Interference against a newly labeled substance with ruthenium sulfonate complexes showing discrepant thyroid function...

Area of Science:

• Clinical Chemistry
• Immunology
• Endocrinology

Background:

• Thyroid function tests are crucial for diagnosing and managing thyroid disorders.
• Electrochemiluminescence immunoassays (Elecsys) are widely used for measuring thyroid hormones and antibodies.
• Recent assay improvements may introduce novel sources of analytical interference.

Observation:

• Two patients presented with falsely elevated serum levels of free thyroxine (FT4), free triiodothyronine (FT3), and thyrotropin receptor antibodies (TRAb).
• These abnormalities were detected using updated Elecsys assay kits employing a ruthenium (Ru) sulfonate chemiluminescent agent.
• Patients denied biotin or supplement use, ruling out common interference sources.

Findings:

• Heterophilic blocking tube tests and further investigations revealed the presence of serum antibodies.
• These antibodies specifically interfered with the Ru sulfonate-based assay, causing pseudo-elevations.
• The interference affected FT4, FT3, and TRAb measurements simultaneously, leading to discrepant results.

Implications:

• This is the first report of antibodies to Ru sulfonate complexes causing falsely elevated thyroid function tests and TRAb.
• Clinicians should consider alternative assay methods when encountering unexpected thyroid test results.
• Careful interpretation of thyroid function tests, even with updated kits, is essential to avoid misdiagnosis and incorrect treatment.