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The effects of nonthyroid disease and drugs on thyroid function tests
1Nuclear Medicine Service, Veterans Administration Medical Center, San Francisco, California.
The Medical Clinics of North America
|January 1, 1991
Summary
Serious nonthyroid illness and starvation alter thyroid function tests, often mimicking thyroid disease. Most sick patients remain euthyroid, but certain drugs like dopamine can cause central hypothyroidism.
Area of Science:
- Endocrinology
- Internal Medicine
- Thyroidology
Background:
- Systemic illness and caloric deprivation significantly impact thyroid hormone levels.
- Understanding these effects is crucial for accurate thyroid function assessment in non-thyroidal illness.
Purpose of the Study:
- To elucidate the pathophysiological basis of thyroid hormone alterations in non-thyroidal illness.
- To review common and uncommon patterns of thyroid function test abnormalities.
- To discuss the influence of certain medications on thyroid hormone economy.
Main Methods:
- Review of existing literature on thyroid hormone regulation and metabolism in illness.
- Discussion of common thyroid function test patterns (e.g., decreased T3, variable T4).
- Analysis of drug effects on thyroid hormone indices and TSH secretion.
Main Results:
- The most common pattern involves decreased serum T3, normal or low total T4, and normal free T4.
- A less frequent pattern shows elevated total and free T4 with normal T3, seen in acutely ill patients.
- Dopamine and high-dose glucocorticoids can suppress TSH, leading to central hypothyroidism.
Conclusions:
- Most patients with serious nonthyroid illness are euthyroid despite altered thyroid function tests.
- Accurate assessment requires considering the effects of illness severity, nutritional status, and medications.
- Advanced assays for TSH and free T4 improve diagnostic accuracy in these complex cases.