FREE THYROXINE- FT4
Pre-test preparation or requirements
• Sample can be drawn at any time. But preferred early morning fasting.
• Sample should taken in plain vial.
0.6- 1.2 ng/dl
Significance of test
Serum T3, T4 & TSH measurements form the three components of Thyroid screening panel, useful in diagnosing various disorders of Thyroid gland function.
Primary hypothyroidism is accompanied by depressed serum T3 and T4 values and elevated serum TSH level.
Primary hyperthyroidism is accompanied by elevated serum T3 and T4 levels along with depressed TSH values.
Normal T4 levels are accompanied by increased T3 in patients with T3 thyrotoxicosis.
Slightly elevated T3 levels may be found in pregnancy and estrogen therapy, while depressed levels may be encountered in severe illness, renal failure and during therapy with drugs like propranolol and propyl thiouracil.
Although elevated TSH levels are nearly always indicative of primary hyporthyroidism, and may be seen in secondary thyrotoxicosis.