Thyroxine, Free (FT4)

Code

5965

Principle

Free T4 regulate normal growth and development by maintaining body temperature and stimulating calorigenesis. In addition, free T4  affect all aspects of carbohydrate metabolism as well as certain areas of lipid and vitamin metabolism. Clearly elevated free T4 levels support the clinical findings of a diagnosis of hyperthyroidism while clearly low free T4 levels coupled with appropriate clinical findings, can establish a diagnosis of hypothyroidism.

Preanalytical

1 mL Serum Refrigerated

Turn Around Time

1 day

Methodology

Chemiluminescent immunoassay (CLIA)

Limitations

Non-thyrometabolic disorders may cause abnormal free T4 levels, Anticonvulsant drug therapy (particularly phenytoin) may result in decreased free T4 levels and patients on heparin therapy may have elevated free T4 levels.