Specimen

3 mL (1.5 mL min.) Serum from 1 SST. Ship refrigerated or frozen.

Usage

Assays detecting unbound or free form of thyroid hormones are highly sensitive to detect thyroid dysfunction. They reflect the active form of the hormone, unaffected by non-thyroidal factors. Use of TSH alone as a screening test may be misleading, hence simultaneous measurement of free T3 & T4 are important. TSH should not be used as an isolated laboratory test to assess thyroid function specially in patients with suspected or known pituitary disease.