What are the effects of illness on thyroid function?

From the Guidelines

Illness can significantly impact thyroid function, and it is crucial to continue taking thyroid medication as prescribed, even during periods of illness, to maintain proper thyroid hormone levels and prevent complications. The effects of illness on thyroid function can be complex, with both hyperthyroidism and hypothyroidism potentially occurring due to various factors such as metabolic stress, inflammation, and changes in medication absorption [ 1 ].

Key Considerations

• Thyroid hormone requirements may increase during illness due to metabolic stress, making it essential to maintain proper levels for recovery [ 1 ].
• Severe illness can temporarily affect thyroid function tests, leading to "sick euthyroid syndrome" or "non-thyroidal illness syndrome," which typically resolves as the patient recovers [ 1 ].
• Monitoring for signs of thyroid imbalance, such as unusual fatigue, heart palpitations, and significant temperature sensitivity, is crucial during illness [ 1 ].

Management Recommendations

• For patients on levothyroxine, maintain the regular dosage schedule, and if a dose is vomited within an hour of taking the medication, retake the dose once the stomach settles [ 1 ].
• If unable to take oral medication for more than a day due to severe illness, contact a healthcare provider for alternative administration methods [ 1 ].
• Stay hydrated and follow up with a doctor after recovery to ensure thyroid levels remain appropriate [ 1 ].

Thyroid Function Tests

• Thyroid function tests should be performed when clinically stable or soon after glycemic control has been established in patients with diabetes [ 1 ].
• Consider testing individuals with type 1 diabetes for antithyroid peroxidase and antithyroglobulin antibodies soon after diagnosis [ 1 ].

By prioritizing thyroid health during illness and following these management recommendations, patients can minimize the risk of complications and ensure optimal recovery [ 1 ].

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Effects of Illness on Thyroid Function

• Illness can affect thyroid function, with changes in thyroid hormone levels occurring in response to severe non-thyroidal illness 2, 3, 4, 5.
• In critically ill patients, thyroid stimulating hormone (TSH), free thyroxine (FT4), and free 3,5,3-triiodo-L-thyronine (FT3) levels may decrease 2.
• The TSH and T4 levels often return to low normal levels, although with continued severe illness they may remain low 2.
• Dopamine, dobutamine, or corticosteroid therapy may also reduce TSH levels 2.

Thyroid Hormone Changes in Critically Ill Patients

• The nonthyroidal illness syndrome, also known as the low T3 syndrome or euthyroid sick syndrome, is characterized by abnormal thyroid function tests encountered in patients with acute or chronic systemic illnesses 5.
• Laboratory parameters of this syndrome include low serum levels of triiodothyronine (T3) and high levels of reverse T3, with normal or low levels of thyroxine (T4) and normal or low levels of thyroid-stimulating hormone (TSH) 5.
• This condition may affect 60 to 70% of critically ill patients 5.

Treatment and Outcome

• There are no clinical data that have shown a consistent reduction in mortality with thyroid hormone treatment in the critically ill patient 2.
• Data on the beneficial effect of thyroid hormone treatment on outcome in critically ill patients are so far controversial 5.
• Early recognition and treatment of a hypothyroid state superimposed on critical illness may contribute to recovery from hypotension or the need for mechanical ventilation 6.

Diagnosis and Monitoring

• Abnormal thyroid function tests are commonly found in the critically ill patient and do not require treatment, unless clinical signs of thyroid disease are present 2, 3.
• Thyroid testing should be readily available for any acutely ill patient with any clinical features that suggest thyroid dysfunction, and for groups at increased risk of thyroid dysfunction 3.
• Diagnosis of thyroid dysfunction should be based on the T4-TSH relation rather than either value alone 3.