Misleading FT4 and FT3 Due to Immunoassay Interference From Autoantibodies

Immunoassays used to measure total and free thyroxine (T4 and FT4) and total and free triiodothyronine (T3 and FT3) can provide inaccurate results due to interference from endogenous autoantibodies. A 74-year-old female treated for hypothyroidism with levothyroxine replacement had elevated thyroid s...

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Bibliographic Details
Published in:Clinical biochemistry 2022-03, Vol.101, p.16-18
Main Authors: Goettemoeller, Travis, McShane, Adam J., Rao, Pratibha
Format: Article
Language:English
Subjects:
Aged
Autoantibodies - immunology
Diagnostic Errors
Female
Humans
Immunoassay
Pituitary Neoplasms - diagnosis
Thyroid
Thyroid Function Tests
Thyroid hormone autoantibodies
Thyroid hormone interference
Thyroid Hormone Resistance Syndrome - diagnosis
Thyrotropin - blood
Thyroxine
Thyroxine - blood
Thyroxine - immunology
Triiodothyronine
Triiodothyronine - blood
Triiodothyronine - immunology
TSH
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Summary:Immunoassays used to measure total and free thyroxine (T4 and FT4) and total and free triiodothyronine (T3 and FT3) can provide inaccurate results due to interference from endogenous autoantibodies. A 74-year-old female treated for hypothyroidism with levothyroxine replacement had elevated thyroid stimulating hormone (TSH), FT4, and FT3. Due to concern for hyperthyroidism, levothyroxine was discontinued and further workup was initiated. A pituitary MRI revealed a microadenoma but the alpha-subunit was normal. She was given octreotide for suspected TSH secreting pituitary adenoma without improvement in her TSH, FT4, or FT3 levels. She was referred to our clinic, where inaccurate lab values for FT4 and FT3 were suspected. Testing via equilibrium dialysis liquid chromatography tandem mass spectrometry (LC-MS/MS) method revealed lower levels of FT4 and FT3. Subsequent testing included heterophile blocking tube treatment, polyethylene glycol (PEG) precipitation, and anti-T3/T4 autoantibody levels. The tests revealed thyroid hormone autoantibodies (THAAs) as the cause of immunoassay interference. When thyroid hormones are elevated and TSH is not suppressed, confirmatory testing with another method such as equilibrium dialysis LC-MS/MS, which is not susceptible to interference from autoantibodies, should be considered.
ISSN:0009-9120
1873-2933
DOI:10.1016/j.clinbiochem.2021.11.015