Free T4 (Thyroxine) Test

A free thyroxine test is performed in the following conditions:

• Abnormal findings of thyroid function tests
• Hypopituitarism (less production of hormones by the pituitary gland)
• Presence of lump or nodule in the thyroid gland
• Enlarged thyroid gland
• Problems and complications in pregnancy

Common symptoms of hyperthyroidism (overactive thyroid) are 

• Anxiety
• Weight loss
• Increased heart rate
• Weakness
• Diarrhoea
• Difficulty in sleeping
• Tremors
• Puffiness around the eyes
• Sensitivity to light
• Irregularities in the menstrual cycle in females (Read more: Irregular period causes)

Common symptoms of hypothyroidism (underactive thyroid) include:

• Sudden weight gain
• Constipation
• Dryness of the skin
• Fatigue
• Hair loss
• Intolerance to cold
• Puffiness in the skin
• Irregularities in the menstrual cycle in females

No specific preparation is usually needed for thyroxine test. It can be done at any time during the day, and no fasting is required before undergoing this test. However, some medicines can alter the results of this test; so, make sure to inform your doctor if you are on any medications. He/she can advise you to stop certain medications that can alter test results.

If you are on any thyroid medication, it is best to take the test before taking them. Also, the test should be avoided in case the person is suffering from an acute illness.

For this test, a sample of blood will be collected from a vein of your arm using a needle. The needle injection site will first be cleaned with alcohol. A blood sample will then be withdrawn in a tube and the injection site will be pressed firmly with a cotton or gauze pad to stop bleeding. The collected sample will be sent to a lab for examination.

The whole process is painless and noninvasive, but a few patients experience slight redness in the area of needle insertion. The redness can be minimised by placing an ice pack over the affected area. If you notice persistent discomfort, check in with your doctor at the earliest.

Results of a thyroxin test can vary depending upon the method used and the age, gender, and past health history of the patient. 

Normal results: The normal range of free thyroxine is 10-26 picomoles per litre (pmol/L).

Abnormal results: Higher than normal T4 level could be due to these conditions:

• Thyroiditis (inflammation of thyroid gland)
• Graves disease (an autoimmune disorder)
• Toxic goitre
• Toxic thyroid nodules
• Increased intake of thyroid hormone medicines
• Consuming foods that contain iodine (it is rare and occurs in cases of thyroid problems)
• Certain tumours of the testes or ovaries (rare)

If T4 level appears to be lower than normal, it could be due to these conditions:

• Hypothyroidism
• Malnutrition or fasting (lack of sufficient food)
• Certain medicines
• Severe acute illness

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.