Can Acute Infections or Antibiotics Falsely Affect TSH Levels?
Yes, both acute infections and certain antibiotics can significantly alter TSH levels, potentially leading to misleading thyroid function test results that may not reflect true thyroid status. This is particularly important to recognize when evaluating thyroid function during illness.
Effects of Acute Infections on TSH Levels
Acute illnesses can cause transient elevations in TSH levels that do not necessarily indicate underlying hypothyroidism 1. In one study of elderly hospitalized women, 4.2% of patients had transient TSH elevations due to acute non-thyroidal illness 1.
COVID-19 infection specifically can disrupt the hypothalamus-pituitary-thyroid axis through multiple mechanisms, including virus-related hypophysitis affecting central TSH regulation, subacute thyroiditis, or low T3 syndrome (non-thyroid illness syndrome) 2.
Subacute thyroiditis, an inflammatory condition of the thyroid that can occur following viral infections, may cause fluctuations in thyroid hormone and TSH levels during different phases of the illness 3.
Effects of Antibiotics on TSH Levels
Rifamycins (including rifampin and rifabutin) can affect thyroid function tests by increasing the metabolism of thyroid hormones, potentially requiring increased doses of levothyroxine in patients on thyroid replacement therapy 4.
When patients take rifamycins, monitoring of serum TSH is recommended as they may require increased doses of levothyroxine to maintain euthyroid status 4.
Mechanisms of Interference
During serious non-thyroidal illness, the most common pattern of alterations in thyroid function tests includes decreased serum T3 concentration, normal or low total serum T4 level, and normal free T4 concentration 5.
Certain drugs can confound thyroid test interpretation. Dopamine and high-dose glucocorticoids can suppress TSH secretion from the pituitary and potentially cause central hypothyroidism 5.
TSH levels can vary by as much as 50% of mean values on a day-to-day basis, with up to 40% variation in values obtained from serial TSH measurements performed at the same time of day 4.
Clinical Implications and Recommendations
TSH results obtained during acute illness should be interpreted cautiously, as they may not reflect true thyroid status 1.
For genuine assessment of thyroid status, both TSH and FT4 levels should be determined together, especially in patients with acute illness 6.
Patients who present with primary adrenal insufficiency can have TSH levels that are usually in the range of 4–10 IU/L due to the lack of the inhibitory effect of cortisol on TSH production 4.
In patients with severe COVID-19 infection, routine thyroid function tests are encouraged to detect potential thyrotoxicosis, and thyroid function should be reassessed after recovery to identify potential hypothyroidism 2.
Special Considerations
Interpretation of TSH results in screening tests differs in certain population groups including children under 14, pregnant women, the elderly, and patients with non-thyroidal illnesses 6.
In pregnant women with hyperemesis gravidarum, biochemical hyperthyroidism (undetectable TSH level, elevated FTI) may be present but is rarely associated with clinical hyperthyroidism and usually requires no treatment 4.
Iodine status can affect thyroid function tests. In iodine-deficient individuals who suddenly increase iodine intake, there may be transient changes in thyroid function tests including TSH 4.