Antibody interference in a two-site immunometric assay for thyrotrophin

Area of Science:

• Clinical Chemistry
• Endocrinology
• Immunoassay Technology

Background:

• Thyroid function testing is crucial for diagnosing thyroid disorders.
• Immunoassays, particularly two-site immunoenzymometric assays, are widely used for measuring thyrotropin (TSH).
• Assay interference can lead to inaccurate diagnostic results, impacting patient care.

Purpose of the Study:

• To investigate the cause of erroneously high thyrotropin values in a specific two-site immunoenzymometric assay.
• To identify methods for correcting or removing the observed assay interference.

Main Methods:

• Analysis of 1585 consecutive serum samples using a two-site immunoenzymometric assay for thyrotropin.
• Testing the effect of adding various animal sera (mouse, newborn calf, horse, sheep, rabbit) on assay results.
• Evaluating the role of horseradish peroxidase as a label in the interference.
• Assessing the efficacy of adding mouse serum and anti-immunoglobulin M (anti-IgM) to eliminate interference.

Main Results:

• Fourteen out of 1585 samples showed erroneously high thyrotropin values.
• Adding mouse or newborn calf serum did not correct the interference initially.
• Increased concentrations of mouse serum, but not other animal sera, reduced the interference in follow-up samples.
• The interference was specific to assay systems using horseradish peroxidase, not radioiodine (125I).
• Successful removal of interference was achieved by adding mouse serum and anti-IgM to the assay reagents.

Conclusions:

• A specific interference, leading to falsely elevated thyrotropin levels, can occur in certain immunoenzymometric assays.
• This interference is linked to the use of horseradish peroxidase as a label and potentially to immunoglobulin interactions.
• The addition of mouse serum and anti-immunoglobulin M provides a reliable method to eliminate this interference in thyrotropin testing.