Clinics and Departments

Laboratory Services

Lab Dept:

Chemistry

Test Name:

FREE TRIIODOTHYRONINE (FT3)

General Information

Lab Order Codes:

FT3

Synonyms:

Free T3; FT3

CPT Codes:

84481 – Triiodothyronine T3; free

Test Includes:

Free triiodothyronine concentration reported in pg/mL.

Logistics

Test Indications:

Free Triiodothyronine (T3) is a second or third level test of thyroid function. It provides further confirmation of hyperthyroidism, supplementing the tetraiodothyronine (T4), sensitive thyrotropin (sTSH), and total T3 assays. Monitoring thyroid hormone replacement.

Lab Testing Sections:

Chemistry - Sendouts

Referred to:

Mayo Medical Laboratories (MML Test: 9404/FRT3)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

1 - 3 days

Special Instructions:

N/A

Specimen

Specimen Type:

Blood

Container:

Red top tube

Draw Volume:

1.8 mL (Minimum: 1.5 mL) blood

Processed Volume:

0.6 mL (Minimum: 0.5 mL) serum

Note: Submission of the minimum volume does not allow for repeat analysis and may results in QNS (quantity not sufficient) test results.

Collection:

Routine venipuncture

Special Processing:

Lab Staff: Centrifuge specimen, remove serum into a screw-capped round bottom plastic vial. Store and ship at refrigerated temperatures. Forward promptly.

Patient Preparation:

None

Sample Rejection:

Gross hemolysis; warm specimens; mislabeled or unlabeled specimen

Interpretive

Reference Range:

Age

Range

<1 year:

Reference values have not been established for patients that are less than 12 months of age.

≥1 year:

2.0 – 3.5 pg/mL

Critical Values:

N/A

Limitations:

FT3 is not a sensitive test for hypothyroidism.

Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating anti-animal antibodies present. These anti-bodies may interfere with the assay reagents to produce unreliable results.

Methodology:

Immunoenzymatic Assay

References:

Mayo Medical Laboratories April 2011



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