Report CPT 84439 for a test measuring free thyroxine (free T4) for patients with abnormal thyroid stimulating hormone (TSH).
1. What Is CPT Code 84439?
CPT 84439 covers a test in a patient’s specimen (usually serum) for free T4 (thyroxine).
This often gets ordered by clinicians for the evaluation of patients with abnormal thyroid stimulating hormone (TSH).
Elevated free thyroxine levels can indicate hyperthyroidism (for example, Graves’ disease). Low levels, on the other, can indicate other types of hypothyroidism (for example, Hashimoto’s disease)
The CPT book describes CPT code 84438 as: “Thyroxine; free.”
The 84438 CPT code procedure begins with a lab analyst receiving the patient’s specimen (usually serum) before they start with the technical steps required to mix it with substances for measuring free thyroxine (T4).
Free thyroxine (4) is not bound to proteins in the patient’s blood and is the active form of thyroxine. Thyroxine is one of the thyroid gland’s major hormones, together with triiodothyronine (T3).
Triiodothyronine (T3) controls energy use, metabolism, and many body functions.
This procedure can use methods such as immunoassay to determine the amount of free thyroxine in the patient’s specimen. The immunoassay method uses reagent antigens and lets them react with antibodies.
4. Billing Guidelines
Report CPT 84436 instead of CPT 84438 for a total thyroxine test (both the bound and unbound, or free, T4).
You may want to bill the specimen collection separately if your payer requires that. In that case, you can use CPT 36415 to collect venous blood by venipuncture.