T4 Free (FT4)
Quest Diagnostics
Sample type: Serum
Requires fasting: No
Phlebotomy required
Details
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).
- Free T4
Estimated days for results: Results should be available in 2 - 5 business days after the sample is collected
Details
T4 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
3–5 business days
<1 Month Not established
1-23 Months 0.9-1.4 ng/dL
2-12 Years 0.9-1.4 ng/dL
13-20 Years 0.8-1.4 ng/dL
>20 Years 0.8-1.8 ng/dL
1-23 Months 0.9-1.4 ng/dL
2-12 Years 0.9-1.4 ng/dL
13-20 Years 0.8-1.4 ng/dL
>20 Years 0.8-1.8 ng/dL
Blood Draw Options with Fullscript
Fullscript offers several convenient phlebotomy options to complete your lab testing:
Quest Diagnostics Patient Service Centers (PSC)
- Location: Visit a nearby Quest Diagnostics Patient Service Center.
- Cost: $10 sample collection fee (paid during lab order checkout).
- Scheduling: Schedule your appointment here. Appointments are recommended to reduce wait times. Walk-ins are accepted, but may experience delays. Aim to arrive 10 minutes before your appointment.
- Collection Instructions:
- Bring a valid ID.
- Bring your digital or printed requisition form, available in the Labs tab of your Fullscript account.
- Check-in: Scan the QR code from your confirmation email or follow kiosk instructions.
- More Info: Quest Diagnostics blood draw guide
Getlabs Mobile Phlebotomy
- Location: Sample collection at your home or office.
- Cost: $85 sample collection fee (paid during lab order checkout).
- Availability: Available in most locations – enter your ZIP code during checkout to confirm.
- Scheduling: Schedule your appointment here through your Fullscript account.
- Collection Instructions:
- Have your digital or printed requisition form and valid ID ready.
- Your phlebotomist will contact you by phone to coordinate arrival.
- More Info: Getlabs blood draw guide
Specimen
- Preferred Specimen(s): 1 mL serum
- Alternative: NA
- Minimum Volume: 0.3 mL
- Collection Instructions: NA
Storage and shipping instructions
- Transport Container: Serum separator tube (SST)
- Transport Temperature: Room Temperature
- Specimen Stability:
- Room temperature: 7 days
- Refrigerated: 7 days
- Frozen: 28 days
- Reject Criteria: NA
State restrictions:
Patient can't order this test if they are located in Hawaii, Puerto Rico, New Jersey, New York, or Rhode Island
