Goettemoeller Travis, McShane Adam J, Rao Pratibha
Internal Medicine Residency Program, Cleveland Clinic Foundation, Cleveland, OH, USA.
Department of Laboratory Medicine, Cleveland Clinic Foundation, Cleveland, OH, USA.
Clin Biochem. 2022 Mar;101:16-18. doi: 10.1016/j.clinbiochem.2021.11.015. Epub 2021 Nov 27.
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.
用于测量总甲状腺素和游离甲状腺素（T4和FT4）以及总三碘甲状腺原氨酸和游离三碘甲状腺原氨酸（T3和FT3）的免疫测定法，可能会因内源性自身抗体的干扰而得出不准确的结果。
一名74岁女性，因甲状腺功能减退接受左甲状腺素替代治疗，其促甲状腺激素（TSH）、FT4和FT3升高。由于担心甲状腺功能亢进，停用了左甲状腺素并开始进一步检查。垂体磁共振成像（MRI）显示有一个微腺瘤，但α亚基正常。因怀疑为分泌TSH的垂体腺瘤，她接受了奥曲肽治疗，但其TSH、FT4或FT3水平并未改善。她被转诊至我们的诊所，怀疑FT4和FT3的实验室值不准确。
通过平衡透析液相色谱串联质谱（LC-MS/MS）法检测发现FT4和FT3水平较低。后续检测包括嗜异性抗体阻断管处理、聚乙二醇（PEG）沉淀以及抗T3/T4自身抗体水平检测。检测结果显示甲状腺激素自身抗体（THAA）是免疫测定干扰的原因。
当甲状腺激素升高而TSH未被抑制时，应考虑采用另一种不易受自身抗体干扰的方法，如平衡透析LC-MS/MS进行确证检测。
