Clinics and Departments

Laboratory Services

Lab Dept:

Chemistry

Test Name:

T4 (THYROXINE) TOTAL, SERUM

General Information

Lab Order Codes:

T4

Synonyms:

T4 Total, Thyroxine

CPT Codes:

84436 – Thyroxine; total

Test Includes:

Thyroxine concentration reported in ug/dL.

Logistics

Test Indications:

Thyroxine is a hormone synthesized and secreted by the thyroid gland and plays an important role in regulating metabolism. T4 is secreted into the circulation in response to the pituitary hormone, TSH. T4 measurements provide information on thyroid function.

Lab Testing Sections:

Chemistry (all specimens tested on the St. Paul campus)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

1 – 3 days, test performed Monday – Friday.

Special Instructions:

N/A

Specimen

Specimen Type:

Blood

Container:

Red top (plain, no gel) tube

Draw Volume:

1.5 mL (Minimum: 0.6 mL) blood

Processed Volume:

0.5 mL (Minimum: 0.2 mL) serum

Collection:

Routine venipuncture

Special Processing:

Lab Staff: Centrifuge specimen, remove serum aliquot into a plastic sample cup. Store at refrigerated temperatures.

Patient Preparation:

None

Sample Rejection:

Mislabeled or unlabeled specimen; specimens other than serum; gross hemolysis

Interpretive

Reference Range:

Age:

Range (ug/dL):

0 days:

8.3 – 19.0 ug/dL

1 – 6 days:

10.0 – 20.0 ug/dL

7 – 30 days:

7.5 – 15.4 ug/dL

1 month – 1 year:

5.2 – 15.9 ug/dL

> 1 year:

4.6 – 11.2 ug/dL

Critical Values:

N/A

Limitations:

Heterophile antibodies may interfere with immunoassay testing. The drug phenytoin may interfere with the T4 assay due to competition for TBG binding sites.

Methodology:

Competitive Immunoassay/Chemiluminescence

References:

DPC End User Procedure Manual Disk #0408111 (2005)

Siemens Immulite Total T4 product insert (07/29/2008) PIL2KT4-21

National Committee for Clinical Laboratory Standards (NCCLS) (2002) Clinical Laboratory Technical Procedure Manuals; Approved Guideline-Fourth Edition GP2-A4

Biorad Immunoassay Plus Control Product Insert

Burtis, CA, Ashwood, ER, Bruns, DE, editors (2006) Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th Edition, Philadelphia: W.B. Saunders, 2006.

Jacobs and DeMott Laboratory Test handbook (2001) 5th Edition, Lexi-comp Inc



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