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Interference in free thyroxine immunoassay

Sujoy Ghosh1, Michael Howlett, David Boag

  • 1The Ayr Hospital, Dalmellington Road, Ayr KA6 6DX, United Kingdom. drsujoyghosh@rediffmail.com

European Journal of Internal Medicine
|April 9, 2008
PubMed

Insights

False free thyroxine (T4) results due to heterophile antibody interference caused clinical confusion in two patients. Repeat testing at another lab confirmed normal thyroid function, highlighting assay interference issues.

Area of Science:

  • Clinical Chemistry
  • Endocrinology
  • Immunology

Background:

  • Thyroid function tests are crucial for diagnosing thyroid disorders.
  • Free thyroxine (T4) and thyroid-stimulating hormone (TSH) are key biomarkers.
  • Non-specific symptoms like tiredness can prompt thyroid testing.

Observation:

  • Two patients presented with tiredness, leading to thyroid function tests.
  • Initial tests showed high free T4 with normal TSH.
  • Results were consistent within the same laboratory and assay.

Findings:

  • Discrepancies between clinical presentation and lab results prompted further investigation.
  • Repeat testing at a different laboratory using a different assay revealed normal free T4 and TSH.
  • Heterophile antibodies were identified as the cause of interference in the initial free T4 assay.

Implications:

  • Assay interference by heterophile antibodies can lead to misdiagnosis and clinical confusion.
  • The importance of considering antibody interference in discordant thyroid function test results.
  • Validation of results through alternative testing methods is critical for accurate patient care.

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