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.