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T4
T4 (THYROXINE), TOTAL, SERUM

Test Code T4 
Test T4 (THYROXINE), TOTAL, SERUM 
Methodology Electrochemiluminescence Immunoassay (ECLIA) 
Description Useful for aiding in the diagnosis of hypothyroidism and hyperthyroidism; assessing thyroid function in patients with normal thyroxine-binding globulin levels; monitoring patients on hormone replacement therapy. Synthetic T3 causes decreased total T4.

NOTE: This test, when ordered on Medicare patients, is subject to the National Coverage Determination (NCD) policy "Thyroid Testing". Please verify that the diagnosis code (ICD-9) you have chosen demonstrates medical necessity for the test as documented in the physician's patient record. The CMS web site or the NorDx Limited Coverage Documentation Guide are available to assist you with this verification. A properly executed Advance Beneficiary Notice (ABN) must be submitted with the specimen if medical necessity is not demonstrated by the ICD-9 code chosen.

No sample should be collected on patients receiving therapy with high biotin doses (i.e. biotin therapy for Multiple Sclerosis or oncology patients; skin, hair and nail supplements, or multivitamins containing > 5 mg/day) until at least 12 hours after the last biotin administration. If unsure, or if the clinical picture does not fit the results please contact the laboratory . We have methods to check for biotin interference as well as for any other interferences and for the accuracy of the results.

Biotin interference would falsely increase the result of this assay. 

Specimen Draw blood in either a plain, red-top tube or serum gel tube. Spin down and send 1.0 mL (minimum volume: 0.5 mL) of serum refrigerated. 
Reference Values Adult:
5.3 - 12.3 g/dL

Pediatric:
Ages: 1 - 3 yrs: 6.8 - 13.5 g/dL
Ages: 3 - 10 yrs: 5.5 - 12.8 g/dL 

Analytic Time 1 Day 
Day(s) Test Set Up Monday through Sunday 
CPT Code(s) 84436