Thyroxine, Free
(FT4)

Sample type:-

• Serum (preferred)

• Plasma (lithium heparin)

Uses:-

1. measure the amount of free T4 in your blood. Free T4 is the thyroxine that is not attached to a protein in the blood.

2. used to monitor people who are being treated for thyroid problems.

3. FT4 assays are prone to inaccurate readings in pregnant women. The studies have shown that FT4 index measurement is more reliable than free T4 immunoassays in pregnant women.

Precautions:-

• Medications or supplements that contain biotin (vitamin B7) can affect the results so the patient should stop taking any medicines or supplements at least 72 hours before sample collection.

Interfering factors:-

1. medicines, such as phenobarbital, can affect your free T4 levels. Severe chronic illnesses, such as chronic renal failure and cirrhosis of the liver, can also affect the test.

2. Pregnancy and some diseases, including kidney and liver disease, can also affect the results of this test.

3. Medications or supplements that contain biotin (vitamin B7) can affect the results.

Pre- analytical errors:-

1. Citrate plasma specimen

2. Unlabeled or mislabeled specimen

3. The patient takes supplements that contain biotin and comes to laboratory to do the test.

The Corrective action:-

1. Reject the sample and require another one and make sure that it drawn on a red top tube or green top tube.

2. Reject the sample and another sample will requested and make sure that all data of the patient is correct.

3. Tell the patient to avoid taking biotin at least 72 hours before sample collection.

Post analytical errors:-

1. Write wrong name on the report.

2. Send wrong results to the patient.

The Corrective action:-

1. Make sure that the name and all data are right

2. Communicate to the patient and apologize for this mistake and sent the right report to him.

Reference range :-

Adults :0.58–1.64 ng/dL.

Pregnant women:

First trimester: 0.73–1.13 ng/dL

Second trimester: 0.54–1.18 ng/dL