Single best test for diagnosis of hypothyroidism is estimation of

Ans. c (TSH). (Ref. Harrison, Principles of Medicine, 15th ed. 2066)# A normal TSH level excludes primary (but not secondary) hypothyroidsm.# If TSH is elevated, a free T4 level is needed to confirm presen ce of clinical hypothyroidism, but free T4 is inferior to TSH when used as screening test, as it will not detect subclinical or mild hypothyroidsm.# Circulating free T3 levels are normal in about 25% patients, reflecting adaptive response to hypothyroidism. T3 levels are therefore not indicated.# For congenital hypothyroidism even TSH/T4 levels in heel-prick blood specimens are used for neonatal screening.# Note: Iodine deficiency remains the most common cause of hypothyroidsm.