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Thyroid tests measure how well your thyroid gland is working. The thyroid test detects whether your thyroid gland is overactive or underactive. It also hints at other related conditions. 

Thyroid Tests

Thyroid tests such as TSH measure the amount of thyroid hormone in your blood and diagnose thyroid disease. However, whether to undergo fasting before taking a thyroid test is a huge confusion because studies have shown variations in TSH levels tested with and without fasting. 

Types of thyroid tests: TSH, T4, & T3. 

Following are the various types of thyroid tests: 

Types of thyroid tests

1) TSH Test

The TSH is produced in the pituitary gland in the brain. The pituitary gland produces more TSH when thyroid levels get low in your body – the production of more TSH in the pituitary serves as a signal for the thyroid gland to compensate and release more thyroid hormones. 

Similarly, the pituitary gland makes less TSH when thyroid levels are high. Therefore, the TSH levels can help detect whether your thyroid is working well. 

2) T4 Test 

T4 is the primary form of thyroid hormone that circulates in the blood. It helps measure the blood level of the hormone T4 (thyroxine). 

3) T3 Test 

It measures the other thyroid hormone, T3 (Triiodothyronine). T3 tests are often used to diagnose hyperthyroidism or its severity. 

How many hours of fasting are required for a thyroid test? 


There is no such requirement as fasting before undergoing a TSH test. However, your pathologist will be a better person to guide you. 

You may be asked to fast for at least 8-10 hours when you have to undergo other health tests along with thyroid hormone levels. Also, you can definitely have water when you are fasting.

What is the best time to be tested? 

If you take the test after overnight fasting in the morning, the result may show high TSH levels. It is compared to tests done later in the day without fasting. 

It creates a problem in the detection of subclinical hypothyroidism. It occurs when you have mildly elevated TSH levels and normal Free T4 (Active form of T4) with no symptoms. The condition can be diagnosed and monitored based only on TSH, as T4 and T3 usually remain normal.

If you take the test later in the afternoon without fasting, your TSH levels will be low, and due to this, subclinical hypothyroidism may be missed. Always get tested at the same time, in the same manner, and at the same lab to avoid inconsistency and get accurate results. 

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A word from Grace 

The TSH test is the best way to diagnose and monitor thyroid diseases. However, TSH levels vary based on factors such as your age, thyroid condition, and also on your sleeping cycle or when you last ate.  

Despite normal TSH levels, you may show symptoms in some cases. And sometimes “normal” TSH may also be abnormal. In such cases, look for immediate medical help.

For more information, visit us at Grace Laboratory


1) Can I drink tea before thyroid test?

There are no such rules as not consuming anything before a thyroid test. However, if your health caretaker has asked you to do fasting, you should avoid drinking tea too. 

2) Can I drink water before thyroid test?

Yes, you can have water before undergoing a thyroid test. 

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