Thyroxine, Total
(T4)

Sample type:-

Serum

Uses:-

1. A total T4 test is conducted to evaluate thyroid gland function; diagnose hypothyroidism or hyperthyroidism; to screen for hypothyroidism in newborns.

2. Monitoring treatment of hyperthyroidism with thiouracil and other anti-thyroid drugs.

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 12 hours before sample collection.

• This test cannot be used in patients receiving treatment with lipid-lowering agents containing dextrothyroxine (D-T4) unless therapy is discontinued for 4 to 6 weeks to allow the physiological state to become reestablished prior to testing.

Interfering factors:-

1. synthetic triiodothyronine (T3)will cause a low total thyroxine (T4)

2. Various drugs can interfere with the test result.

3. Increased total thyroxine (T4) is seen in pregnancy and patients who are on estrogen medication.

Pre-analytical errors:-

1. Hemolysis 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 another one is obtained.

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 12 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:

6.09–12.23 μg/dL