Study note
SurgeryThe thyroid gland

Serum TSH measurement and thyroid function patterns

THE CONTEXT
Serum thyroid-stimulating hormone (TSH) must be interpreted alongside T3 and T4 to identify the thyroid functional state.

Measurement and interpretation

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An immunochemiluminometric assay accurately measures TSH even at very low serum concentrations.
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Interpretation of an abnormal TSH result depends on the accompanying T3 and T4 values.

Patterns of thyroid function

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In the euthyroid state, T3, T4 and TSH are all within their normal ranges.
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Florid thyroid failure produces depressed T3 and T4 levels with gross elevation of TSH.
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Incipient or developing thyroid failure produces low-normal T3 and T4 values with elevated TSH.
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In toxic states, TSH is suppressed.
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