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Free
T3 levels are useful in the differential diagnosis of
hyperthyroidism and non-thyroidal illness; TSH levels may be
suppressed in both conditions with normal or raised free T4.
Free T3 is not helpful and may be misleading in diagnosis of
hypothyroidsim. Free T3 may also be misleading in monitoring
T3 replacement because of wide variations that depend on the
interval between dose and sampling.
Patients on anti-thyroid treatment may require free T3 levels
to identify persistent drug treatment thyrotoxicosis due to
isolated T3 excess. |