Order Code: 34429
ABN Requirement: No
Synonyms: Free T3; Unbound T3; FT3
Specimen: Serum
Volume: 1 mL
Minimum Volume: 0.5 mL
Container: Gel-barrier tube (SST, Tiger Top)
Collection:
- Collect and label sample according to standard protocols.
- Gently invert tube 5 times immediately after draw. DO NOT SHAKE.
- Allow blood to clot 30 minutes.
- Centrifuge for 10 minutes.
Special Instructions: Samples should not be taken from patients receiving therapy with high biotin doses (>5 mg/day) until at least 8 hours following the last dose.
Transport: Store serum at 2°C to 8°C after collection and ship the same day per packaging instructions provided with the Cleveland HeartLab shipping box.
Stability:
Ambient (15-25°C): 7 days
Refrigerated (2-8°C): 7 days
Frozen (-20°C): 28 days
Causes of Rejection: Samples which are heat-inactivated; samples stabilized with azide; specimens other than serum; improper labeling; samples not stored properly; samples older than stability limits
Methodology: Immunoassay
Turn Around Time: 1 to 3 days
Reference Range:
| Age | pg/mL |
| <1 Month | Not established |
| 1-23 Months | 3.3-5.2 |
| 2-12 Years | 3.3-4.8 |
| 13-20 Years | 3.0-4.7 |
| >20 Years | 2.3-4.2 |
Clinical Significance: “The T3, Free (FT3) test measures serum triiodothyronine (T3) not bound to thyroid hormone-binding proteins (thyroid hormone-binding globulin [TBG], transthyretin, albumin). It is used, primarily in concert with measurement of thyroid-stimulating hormone (TSH, test code 899) and free T4 (FT4, test code 866), in the diagnosis and management of hyperthyroidism and to clarify thyroid hormone status in the presence of a possible thyroid hormone-binding protein abnormality.
The FT3 (or total T3) test is usually ordered following an abnormally low TSH result and/or a clinical picture suggestive of hyperthyroidism, particularly if the free T4 test (FT4, test code 899) result is not elevated. Up to 10% of patients with proven hyperthyroidism (due to Graves disease or an autonomously secreting thyroid nodule) may have an elevated FT3 but normal FT4 (T3 toxicosis), particularly early in the course of disease or as an early sign of relapse after treatment [1]. In contrast, there is limited utility for FT3 testing for suspected hypothyroidism as FT3 levels may not drop until well after both TSH and FT4 rise [2].
References
1. Carle A, et al. Eur J Endocrinol. 2013;169:537-545.
2. Garber JR, et al. Endocrine Pract. 2012;18:988-1028.
The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.