Tri-iodothyronine (T3)

Test ID: 

704327

CPT code:

704327

Synonyms:

Triiodothyronine (T3)

T3, Total

Clinical Use:

Thyroid function which is particularly useful in the diagnosis of T3 thyrotoxicosis, in which T3 is increased and T4 is within normal limits. T3 toxicosis is occasionally found in Graves’ disease. It occurs with a single toxic nodule, multinodular thyrotoxicosis, and following treatment with T3 (Cytomel®). It is increased in and occasionally helpful for confirmation of diagnosis of conventional hyperthyroidism, in which commonly both T3 and T4 levels are increased. T3 is needed in patients with clinical evidence for hyperthyroidism, in whom the usual thyroid profile is normal or borderline.
Reported to be normal to slightly increased with familial dysalbuminemic hyperthyroxinemia.
Recommended for patients with supraventricular tachycardia, for patients with fatigue and weight loss not otherwise explained, or for those with proximal myopathy and in whom T4 levels are not elevated.

Test Information:

Increased T3 often occurs in hyperthyroidism, but in approximately 5% of cases only T3 is elevated, “T3 toxicosis.” Do not confuse T3 with T3 uptake; these are two different tests. The latter is done very commonly as part of the usual thyroid profile. Less than 1% of T3 is unbound.

Specimen Type:

Serum

Requested Volume: 

0.8 mL

Minimum Volume: 

0.3 mL

Container Type: 

Red-top tube or gel-barrier tube

Collection:

If a red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions:

Room temperature

Stability Requirements:

Expected Turnaround Time:

1 to 2 Days

Rejection Criteria

Citrate plasma specimen; improper labeling