From the Guidelines
Several factors, including acute illness and certain medications, can falsely elevate thyroid-stimulating hormone (TSH) levels. According to the U.S. Preventive Services Task Force recommendation statement published in the Annals of Internal Medicine in 2015 1, TSH secretion is highly variable and sensitive to several common factors. Some of these factors include:
- Acute illness
- Certain medications
- Laboratory issues such as heterophilic antibodies or rheumatoid factor
- Assay interference from biotin supplementation
- Certain medical conditions like adrenal insufficiency or TSH-secreting pituitary tumors
- Pregnancy, particularly the first trimester
- Time of day, with TSH typically higher in early morning It is essential to consider these factors when interpreting TSH results, as false-positive results can lead to overdiagnosis and overtreatment 1. When encountering unexpectedly high TSH results that don't match clinical presentation, consider repeating the test, using a different assay method, or testing for other thyroid parameters like free T4 to confirm the finding before initiating or adjusting treatment.
From the Research
Factors that Falsely Elevate TSH
- Macro-TSH interference: This occurs when TSH is complexed with anti-TSH antibodies, leading to falsely elevated TSH levels 2, 3.
- Heterophilic antibodies: These antibodies can interfere with TSH assays, resulting in false positive results 4.
- Anti-ruthenium interference: This type of interference can occur when substances against ruthenium are present, reducing the excitation of ruthenium and resulting in erroneous TSH levels 5.
- Thyroid hormone autoantibodies (THAb): These autoantibodies can also interfere with TSH testing, leading to inaccurate results 2.
Laboratory Interference
- Chemiluminescence immunoassay (CLIA) interference: This technique can be affected by various factors, including macro-TSH and heterophilic antibodies 2, 4.
- Elecsys assay interference: This assay can be affected by anti-ruthenium interference, leading to falsely elevated TSH levels 5.
- Polyethylene glycol (PEG) precipitation test: This test can be used to detect macro-TSH interference, which can falsely elevate TSH levels 3.