T4 Free (FT4)

What this laboratory test evaluates

DetailsT4 Free (FT4) Test – This test measures the amount of unbound thyroxine (T4) in your blood, which is available to your body's cells. It's a key test for diagnosing thyroid conditions like hyperthyroidism (where FT4 levels are high) and hypothyroidism (where FT4 levels are low), including both congenital and acquired forms. The FT4 test is crucial for assessing thyroid function, monitoring thyroid health, and evaluating the effectiveness of treatments.

What patients is this test right for?This test is often used alongside a thyroid-stimulating hormone (TSH) test to diagnose thyroid issues. It's particularly useful for:

• Following up on abnormal TSH results
• Assessing thyroid function in patients with pituitary abnormalities
• Monitoring patients after treatment for Graves' disease
• Adjusting thyroid hormone doses more quickly than TSH tests allow

Why choose this test?The FT4 test is preferred over the total T4 test because it's less influenced by proteins that bind thyroid hormones, making it a more accurate reflection of the thyroid hormones your body can use.

What type of sample is required for this test?1 mL serum. Phlebotomy is required.

Test Resources • https://www.questdiagnostics.com/healthcare-professionals/clinical-education-center/faq/faq294 http://education.questdiagnostics.com/faq/FAQ61

Additional test information

This test measures the amount of unbound thyroxine (T4) in the blood It's a key test for diagnosing thyroid conditions like hyperthyroidism (where FT4 levels are high) and hypothyroidism (where FT4 levels are low).

Collection and processing

• Sample type: Serum
• Fasting: No
• Estimated laboratory processing: Results should be available in 2 – 5 business days after the sample is collected

How Sunridge uses laboratory information

Sunridge considers the medical question, symptoms, history, medications, prior results, and whether the finding could change care before recommending testing. A laboratory result is not interpreted in isolation and does not establish a diagnosis by itself.

Before requesting this test

Availability, collection requirements, eligibility, and processing estimates can change. Sunridge reviews each request and, when appropriate, creates the order through Fullscript. Follow the current instructions supplied with the approved order.