⚠️ Do not check TFTs in ITU unless there is strong suspicion of thyroid disease. Abnormal results are often due to Non-Thyroidal Illness Syndrome (NTIS) and should be repeated after 6–8 weeks when the patient has recovered.

📖 About

Non-Thyroidal Illness Syndrome (NTIS), also called Euthyroid Sick Syndrome, describes abnormal TFTs in acutely ill patients without intrinsic thyroid disease.
Typically: low T3, sometimes low T4, and variable TSH levels — but patient is clinically euthyroid.
Occurs in ~60–70% of ICU patients; strongly associated with sepsis, trauma, and major organ failure.

🧬 Pathophysiology

Decreased T4→T3 conversion: due to reduced deiodinase activity in illness.
Increased reverse T3 (rT3): preferential shunting of T4 to inactive rT3.
HPA axis changes: pituitary suppression alters TSH pulsatility → TSH may be low/normal.
Inflammatory cytokines: IL-6, TNF-α, glucocorticoids, hypoxia all impair thyroid hormone metabolism.

🔑 Causes

Severe systemic illness: sepsis, trauma, MI, burns, CKD, liver cirrhosis.
Starvation & protein-energy malnutrition.
Endocrine/metabolic stress: DKA, adrenal insufficiency.
Medications: amiodarone, corticosteroids, dopamine, iodine contrast, chemotherapy.

🩺 Clinical Features

Patients are usually clinically euthyroid — the symptoms reflect the underlying illness, not thyroid dysfunction.
Discovered incidentally on blood tests in hospital or ICU settings.
Recovery phase: transient rise in TSH may be seen (can mimic subclinical hypothyroidism).

🔎 Investigations

T3: ↓ (hallmark feature).
T4: ↓ or normal.
TSH: variable — low, normal, or mildly ↑; recovery phase often shows TSH rebound.
Reverse T3: ↑ (distinguishes NTIS from true hypothyroidism).
Cortisol: check if adrenal insufficiency suspected.
Repeat TFTs: always after recovery (6–8 weeks) before labelling thyroid disease.

⚕️ Management

👀 Observation: NTIS usually resolves spontaneously once illness improves.
🚫 Avoid thyroxine: do not treat unless clear hypothyroidism (low T4 + low/undetectable TSH with symptoms).
🩺 Treat underlying cause: sepsis, trauma, organ failure, malnutrition.
⚡ Correct metabolic derangements: electrolytes, glucose, adrenal insufficiency if present.
🔁 Repeat TFTs after 6–8 weeks — ensures resolution and rules out primary thyroid disease.

💡 Teaching Pearls:
– Classic finding = low T3, normal/low T4, normal TSH → not hypothyroidism.
– Always think of NTIS if abnormal TFTs in an ICU patient with no thyroid history.
– rT3 rises (unique feature; not raised in primary hypothyroidism).
– A rebound rise in TSH during recovery is normal and should not be misdiagnosed as new hypothyroidism.

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Sick Euthyroid Syndrome