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Interpretation

Thyroid Function Pattern Interpretation

Interpret TSH and free T4 combinations: primary, secondary, and subclinical thyroid disease.

7 min read Thyroid Function
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Educational Interpretation Only

Educational Interpretation Only: This content is for educational purposes and explains common laboratory result patterns. It does not constitute medical advice or diagnosis. Always interpret laboratory results in the context of the patient's clinical condition and consult with a qualified healthcare professional.

Thyroid Function Pattern Interpretation

TSH is the most sensitive first-line test; free T4 (and occasionally free T3) interprets the pattern.

Patterns

  • Low TSH + high free T4: primary hyperthyroidism (Graves disease, toxic nodule, thyroiditis release phase).
  • Low TSH + normal free T4: subclinical hyperthyroidism — confirm with free T3 and consideration of T3 thyrotoxicosis.
  • High TSH + low free T4: primary hypothyroidism (autoimmune Hashimoto thyroiditis is the most common cause).
  • High TSH + normal free T4: subclinical hypothyroidism.
  • Low/normal TSH + low free T4: secondary (central) hypothyroidism — pituitary pathology; obtain a pituitary profile.

Caveats

  • Pregnancy: physiologic changes raise total T4 and lower TSH in trimester 1; use trimesterspecific (or total T4) references.
  • Medications: amiodarone, lithium, and biotin interfere with thyroid assays; biotin causes falsely low TSH on many platforms.
  • Non-thyroidal illness: critical illness can suppress TSH and lower T3/T4 (low T3 syndrome) without intrinsic disease.

Key checks

TSH, free T4, free T3, and — in the right setting — TPO and thyroglobulin antibodies for autoimmune disease.

Clinical Context

Thyroid patterns are inferred from the TSH-to-free-T4 relationship. Recognizing primary, central, and non-thyroidal patterns prevents misdiagnosis in critical illness and pregnancy.

Related Analytes

  • TSH
  • Free T4
  • Free T3
  • TPO Antibody