What Can Affect Your Thyroid Test Results?

It is important that we are proactive in taking thyroid hormone tests to check how well our thyroid glands are doing. The thyroid gland is located at the lower part of your neck. As adults, our thyroid glands create hormones to regulate the metabolism for every cell in our body so it is critical to make sure there isn’t a dysfunction occurring, also known as thyroid disease. Thyroid-stimulating hormone (TSH) levels in your blood reveal how much thyroxine hormones your pituitary gland is asking your thyroid gland to produce. Abnormally high TSH levels can mean you have hypothyroidism – an underactive thyroid. Abnormally low TSH levels can mean the opposite, where your body is producing too much of the thyroid hormone.

Thyroid blood tests are generally very precise but there are instances that an individual’s test results may be affected by certain factors such as fasting, time and location of the blood draw, pregnancy, medications, and serious illness. With that in mind, it is a good idea to be aware of these factors when trying to obtain the most accurate results for you.



Fasting – the act of abstaining from eating or drinking for a period of time, is considered one of the factors that may alter your test results. Many doctors tell patients that fasting is not necessary before the blood test. However, research has shown our TSH levels can decline as much as 26% if we consume foods or drinks before a test. Since many doctors rely on TSH levels to determine a patient is being properly treated with the right dosage, this may result in incorrectly altering their hormone medication. Therefore, it is recommended to test after fasting earlier in the morning to get more accurate results when your TSH levels are in-between fluctuating, as we will discuss next.


Timing & Location

When and where you take your test also matters. Thyroid levels generally lower during the day and rise at night. Ideally, the best time to take the test is during earlier morning hours when the levels are neither too low or high. However, the slight variations should not make a huge difference in your overall test results. It is suggested to keep it uniform by taking your blood draw around the same time for every test to allow comparable results. Also, the results may vary from lab to lab and test to test even if performed at the same laboratory. Each laboratory follows a different set of “normal range” numbers based on different types of equipment, units of measurement, etc. which can change daily depending on quality control. It is a good rule of thumb to compare your result to the normal range numbers of the laboratory associated.



Pregnancy is another factor in influencing the outcome of your blood test due to the increased metabolic requirements. There are changes in the way the thyroid functions during pregnancy, typically increasing about 10% in size. Human chorionic gonadotropin (hCG) and estrogen are two pregnancy-related hormones that may increase the thyroid hormone levels in your blood, causing an inaccurate read. Thyroid hormones play a significant role, especially during the first trimester of pregnancy for the baby’s brain and nervous system development. The baby depends on its mother’s thyroid hormone supply transferred through the placenta during the first three months of pregnancy before the baby’s thyroid starts functioning on its own. It is also highly recommended that newborns are screened for thyroid disorders or as directed by your care provider. According to the American Thyroid Association, doctors should use trimester-specific ranges to determine more accurate TSH levels for pregnant patients.



A person can develop hyperthyroidism from taking certain medications such as Lithium, Iodine/other kelp supplements, Amiodarone, immunomodulating drugs, and tyrosine kinase inhibitors. Particular drugs like iron sulfate, calcium carbonate and proton pump inhibitors can also get in the way of how the body absorbs thyroid hormone replacement. Other medications may affect the laboratory results without affecting the actual functioning of the thyroid including certain anti-convulsants, nonsteroidal anti-inflammatories, blood thinners, and Lasix. Last but not least, avoid taking biotin at least 48 hours prior to your blood draw to prevent incorrect measurements.



Being seriously ill may affect the thyroid functionality causing TSH levels to drop lower than normal. Being sick can cause stress on your endocrine system and adrenal glands which rely on thyroid hormone to function. Low hormone production in addition to body stress as your body simultaneously battles viruses causes fatigue. It is recommended to refrain from taking thyroid blood tests if a patient is extremely sick unless there is strong belief for thyroid disease.


It is important we are dedicated to do what we can to obtain true thyroid blood test results by notifying your doctor of any present factors discussed above before going through with the measurements. Optimal thyroid function is crucial to maintaining a healthy lifestyle. If your results do not seem correct, you can always retake the test as a reasonable next step. Take the initiative to schedule your routine thyroid tests with your doctor or order a thyroid test online with National Discount Labs. We offer a vast variety of blood test packages as well as individual tests at affordable prices to fit your needs for your ease and convenience. Cheers to a being a healthier you.