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Euthyroid Sick Syndrome (Non-Thyroidal Illness)

Altered thyroid hormone pattern (low T3, normal/low TSH) in critically ill patients without primary thyroid disease.

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Endokrinoloji department. Book Appointment →

What is Euthyroid Sick Syndrome (Non-Thyroidal Illness)?

Euthyroid sick syndrome (also called non-thyroidal illness syndrome, NTIS) is the altered thyroid hormone pattern observed in patients with severe acute or chronic illness without underlying thyroid disease.

Common settings include sepsis, major surgery, myocardial infarction, chronic kidney disease, fasting, and malignancy. Reduced peripheral 5'-deiodinase activity decreases T3 and increases reverse T3 (rT3), while suppressed TRH and dopamine reduce TSH.

It is considered an adaptive metabolic response rather than true thyroid failure. Free T4 stays normal early; in prolonged severe illness, free T4 may also fall, indicating poor prognosis.

Symptoms

Often asymptomatic — laboratory finding in critically ill patient
Low total and free T3
Reverse T3 (rT3) elevated
Normal or low TSH
Normal free T4 early; low in severe prolonged illness
Symptoms reflect underlying illness, not thyroid dysfunction

Risk Factors

Sepsis and severe systemic infection
Major surgery and trauma
Acute myocardial infarction
Chronic kidney disease and dialysis
Caloric restriction or starvation
Advanced malignancy
ICU stay and critical illness

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Persistent abnormal thyroid tests during illness
  • New thyroid abnormality without prior thyroid disease
  • Differentiating from central hypothyroidism
  • Persistently abnormal results after recovery (re-test at 6-8 weeks)
  • Suspicion of true thyroid disease (goiter, eye signs)
  • Worsening symptoms despite illness improvement

Treatment Methods

01
Treat the underlying critical illness
02
Routine T4/T3 replacement is NOT recommended
03
Avoid thyroid hormone in absence of true hypothyroidism
04
Recheck thyroid function 6-8 weeks after recovery
05
Endocrinology consult if persistent abnormality
06
Monitor TSH, free T4 and T3 trends
07
Investigate central hypothyroidism if free T4 low

Which Department to Visit?

You can visit our Endokrinoloji department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

Learn About Endokrinoloji Department

Let us help you

You can make an appointment with our specialists or contact us for your concerns.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.