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All CollectionsLab Test InstructionsZRT Laboratory
Free Thyroxine (fT4)
Free Thyroxine (fT4)
Updated over a year ago

Test Details

Lab Company: ZRT
​ Sample Type: Blood Spot
​ Collection Location: At Home

The Free Thyroxine (fT4) test is a single-marker test designed to measure a patient's levels of free thyroxine to help diagnose thyroid imbalance.

Key Details

  • Collection can be done on any day of the month.

  • If you are currently using hormones, supplements, or vitamins, you may need to time your test properly.

  • Avoid anti-aging/anti-wrinkle face creams for 3 days prior to collection.

  • Collect your sample within an hour of waking.

  • Ship samples back to the lab in the provided, prepaid envelope as soon as possible.

Preparation & Timing

  • Collection can be done on any day of the month.

  • Collect your sample within an hour of waking.

  • If you are taking topical, oral, sublingual, or troche hormones,

    • Avoid applying topical hormones with your bare hands for at least two days prior to collection (use latex gloves, an applicator, or a hormone-loaded syringe).

    • Take/apply any night dosage at least 12 hours before your planned morning collection.

    • Avoid using hormones on the face, lips, and neck.

    • Change sheets, pillowcases, and hand towels the night before collection.

    • Avoid touching any surfaces which may be contaminated with hormones.

  • If you are taking hormone patches, vaginal rings, hormone pellets, or hormone injectables, test halfway between doses.

    • For example, 3 days after a once-a-week patch.

  • Avoid taking 7-Keto DHEA for at least 3 days prior to collecting.

  • If you are taking steroids, talk to your healthcare practitioner about proper timing.

  • Avoid anti-aging/anti-wrinkle face creams for 3 days prior to collection.

Collection Instructions

  1. Wash your hands with soap and water.

  2. Dry with a clean towel.

  3. Lay out all materials from the test kit.

  4. Write your name, date, and time of collection on the collection card.

  5. Fold the collection card cover away from the filter paper (which has circles for blood collection). Do NOT touch the filter paper.

  6. Tape the card to a low surface (such as the table) with the filter paper facing out.

  7. Open the sterile gauze and alcohol pad.

  8. Wash and dry your hands again.

  9. Use the alcohol pad to wipe the fingertip you will use for collection.

    1. It is best to use the ring or middle finger on your non-dominant hand.

  10. Remove the lancet’s cap and press the tip against the inside tip of your finger.

  11. Press the tip firmly against your finger until it activates (it should click).

  12. Wipe away the first drop of blood with the sterile gauze.

  13. Position your finger above the collection card.

  14. Gently milk blood from your finger (lightly stroke your finger down to the tip).

    1. Do NOT over-squeeze your finger.

  15. Touch the tip of the drop to the filter paper.

    1. Do NOT touch the paper with your finger.

  16. Place one drop per circle.

    1. Each drop should fill at least ¾ of the circle.

    2. Each drop should saturate the filter paper to the other side.

  17. Collect blood until all circles are filled.
    ​

    1. If blood stops flowing before you are finished, firmly wipe the finger with the gauze to get the blood flowing again.

    2. You can use the second lancet and another finger, if necessary.

  18. Bandage your finger.

  19. Leave the card open to dry for at least 4 hours.

    1. Keep the card in a cool, dry location away from sunlight.

  20. Once the card is dry, fold the cover over the blood spots.

  21. Place the card and completed test requisition form in the test kit.

  22. Place the test kit inside the provided envelope.

  23. Place the prepaid label on the envelope and mail via the carrier indicated on the label.

Requisition & Payment

  • Your kit has been prepaid. You DO NOT need to pay anything extra.

  • Instructions on how to fill out your requisition can be found HERE.

    • Since you pre-paid for your tests, you do not need to fill in the payment information on any of these forms.

Shipping

  • To prepare your sample for shipping,

    1. Place the collection card and completed test requisition form in the test kit.

    2. Place the test kit inside the provided envelope.

    3. Place the prepaid label on the envelope and mail via the carrier indicated on the label.

  • Most samples will be shipped via USPS or UPS. Please check your label to determine the carrier.

  • Ship samples as soon as possible after collection.

Results

  • Results should be released to your provider 3-5 business days after samples are received at the lab. We cannot guarantee processing time.

  • Your provider will notify you when your results are in and schedule a follow-up appointment for you to review them together.

More Resources

Questions?

For general questions, email Rupa Health at support@rupahealth.com. For test-specific questions, contact ZRT by calling 503-466-2445.

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