Should you take thyroid medication before the blood test?

It depends on the specific thyroid test being performed and the instructions provided by your doctor or the laboratory. Some thyroid tests, such as thyroid-stimulating hormone (TSH) or free thyroxine (fT4) tests, may require you to stop taking thyroid medication for a certain period before the blood test to ensure accurate results.

For example, if you are taking thyroid hormone replacement therapy, such as levothyroxine (Synthroid, Levothroid), you may be advised to withhold the medication for 24 to 48 hours before a TSH test. This is because thyroid medication can suppress TSH levels, and taking it too close to the test may result in falsely low TSH results.

On the other hand, some other thyroid tests, such as total T4 or total T3 tests, may not be affected by thyroid medication, and you may be able to take your medication as usual before the test.

To ensure accurate and reliable results, it is essential to follow the specific instructions provided by your doctor or the laboratory regarding whether and when to take your thyroid medication before the blood test. If you have any questions or concerns about the timing of your medication, consult your healthcare provider for personalized guidance.