Total TriIodothyronine (TT3) test

Your doctor may order this test if you have the following symptoms of hyperthyroidism:

• Irritability
• Sleep problems
• Sweating
• Irregular heartbeat
• Unexplained weight loss
• Extreme tiredness
• More frequent bowel movements than usual
• Menstrual irregularity
• Thinning of hair
• Shortness of breath
• Anxiety and mood swings
• Weakness in the arms and legs
• Hand tremors
• Low tolerance for heat
• Eye irritation or bulging eyes
• High blood sugar
• More urination

You may also have to undergo this test if you are at a high risk of hyperthyroidism. 

The following factors put you at risk of hyperthyroidism:

• If you have any other thyroid problem
• If you have a history of long-term illnesses, such as: 
  • Type 1 diabetes
  • Pernicious anaemia, a condition where your body is unable to make healthy red blood cells due to vitamin B12 deficiency
  • Addison’s disease, a condition where your body does not produce a hormone called cortisol
• If you take a lot of iodine-rich foods or iodine-containing medicines
• If you recently had a delivery
• If you are 60 years or older
• If you have a family history of thyroid problems 

You may have this test if you have symptoms of hypothyroidism (thyroid gland does not make sufficient thyroid hormone) which include:

• Low tolerance to cold
• Hair loss
• Slower heart rate
• Constipation
• Loss of consciousness
• Extreme tiredness
• Weight gain
• Eye swelling
• Shortness of breath
• Menstrual irregularity

Additionally, your healthcare practitioner may perform this test if:

• You are on medications for hypothyroidism
• Your pituitary gland does not function normally (a condition called hypopituitarism)

No prior preparations are needed before this test. Inform your healthcare provider about all the herbs, vitamins, supplements, medicines (including over-the-counter drugs) and illegal drugs that you may be taking.

This is because certain medications can alter the blood TT3 levels and affect the test results. Medications that may increase TT3 level in the blood include:

• Clofibrate
• Amiodarone
• Methadone
• Cytomel
• Birth control pills
• Phenothiazines
• Terbutaline
• Tamoxifen
• Valproic acid
• Thyroxine
• Oestrogens
• Certain herbal medicines

Medications that may decrease TT3 level in the blood include:

• Anabolic steroids
• Antithyroid drugs (e.g., methimazole, propylthiouracil)
• Phenytoin
• Amiodarone
• Androgens
• Lithium
• Propranolol
• Aspirin
• Carbamazepine
• Atenolol
• Corticosteroids
• Theophylline
• Furosemide

You may have high or low levels of TBG protein due to genetic or acquired conditions, which may also alter your TT3 values.

Some conditions that show false high TT3 level include:

• Pregnancy
• Liver disease

A laboratory technician will withdraw a blood sample, most commonly from your arm, to perform this test.

You may feel slight pain when the needle pricks your arm. The site may be sore afterwards for a while. If you notice a persistent bruise or an infection, talk to your doctor at the earliest.

Normal results:

The normal level of TT3 in the blood is 75-195 ng/dL (nanograms per decilitre). If you were asked to get this test done to monitor the efficacy of hyperthyroidism treatment, a normal value would indicate that the medicine is effectively controlling the disease.

Abnormal results:

Increased levels of TT3 are seen in conditions such as:

• Thyroid cancer
• Thyroiditis (inflammation of thyroid gland)
• Hyperthyroidism
• T3 thyrotoxicosis, a condition in which a person’s blood has high levels of T3 but normal levels of T4

Decreased levels of TT3 are seen in conditions such as:

• Anorexia nervosa (an eating disorder)
• Congenital TBG deficiency
• Liver disease
• Starvation
• Acute illness
• Long-term illness
• Hypothyroidism
• Kidney failure
• Thyroidectomy (surgical removal of a part/all of thyroid gland)

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.