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What is the Best Time to Have Your Thyroid Levels Tested?

Holtorf Medical Group

Most thyroid-related tests are considered quite accurate. However, there are factors that can influence results which may cause tests to present false or inaccurate data. This is a problem as even minor changes in thyroid levels can cause you to experience major bodily dysfunction. Therefore, it is critical that thyroid testing be as accurate as possible to avoid incorrect diagnosis and dosage.

Being aware of the various factors that can influence your test results and actively taking action to limit such factors can help you acquire proper diagnosis and treatment.

What Influences Thyroid Tests?

It is known that multiple factors influence thyroid test results. Unfortunately, there is not a consensus on the degree to which these factors affect results. However, there is agreement among many medical professionals that patient status and habits do cause significant fluctuations and impact the outcome of thyroid tests.

The following areas can significantly influence thyroid test results and should be considered when scheduling or preparing to have lab work done:

  • The timing of your thyroid medication

  • Whether you are fasting or have consumed food prior to testing

  • If you had certain thyroid-influencing foods such as coffee and alcohol

  • The time of day that the test is done

  • How test results are interpreted by the lab or doctor

Getting the Most Accurate Results

There are two primary factors that cause significant fluctuations in your test results; food and medication.

Fluctuations from Food

Even though common medical guidelines suggest that fasting is not a necessary element of accurate thyroid testing, many studies have shown that fasting in the morning causes TSH levels to increase as much as 26 percent.

Such a significant shift means that you may appear to have subclinical hypothyroidism in the morning while your levels stabilize later in the day once the TSH spike has subsided. This significant factor must be accounted for when one undergoes thyroid testing.

It is common for those administering thyroid tests to indicate whether the patient was fasting or not to account for the difference in TSH levels. However, because thyroid function is unique to the individual there is still a risk of false data and inaccurate diagnosis due to food consumption prior to lab work.

How Medication Muddles Results

Thyroid treatments and medications are intended to stabilize thyroid hormone levels, which can take weeks or months to reach equilibrium.

In general, the timing of your thyroid medication does not significantly influence test results. However, there are situations and certain types of medication that can cause lab results to be skewed dramatically.

T4 Medications: The most common, but not the most optimal, treatment for hypothyroidism is natural or synthetic T4-only thyroid medication. These treatments have a half-life of roughly five to nine days, meaning that it takes about that long for the dosage to reach equilibrium in your system. After this period, the dose will remain consistent as long as you continue to take your medication regularly.

T4 medications have a slower more consistent release time, which is why it is recommended that thyroid levels be tested four to six weeks after treatment has commenced or after your dose has been altered.

Even though T4 takes a relatively long time to stabilize if you take your medication two to four hours prior to testing you may experience a temporary peak that can alter your test results. Furthermore, serum levels can remain elevated for six hours after taking daily replacement medication. For this reason, accuracy may be improved if you have your testing done before taking your daily medication.

Medications Containing T3: In contrast to T4 medication, T3 treatments have a shorter half-life of 18 to 72 hours, meaning that levels fluctuate much quicker than T4. Whereas T4 medications can take days to weeks to significantly impact thyroid levels, T3 formulations can alter blood serum levels in less than a day.

Common T3 containing medications such as Armour, Nature-Throid, WP Thyroid, compounded T4/T3, and Cytomel can cause test results to fluctuate significantly if taken at the wrong time. The best way to improve testing accuracy is to only take combination T4 and T3 medications or T3-only formulations after testing has concluded.

Various studies have shown that those with hypothyroidism who took combination thyroid medications for longer than a single day presented falsely suppressed TSH levels. In response to taking T4 medications, the body’s TSH levels immediately sink and then begin to normalize after roughly five hours. Levels will continue to change until reaching its half-life of approximately 18 hours, where levels will stabilize. If testing must be done after T3 medication is taken, it is best to wait at least 18 hours to allow levels to normalize.

Getting the Tests Your Thyroid Needs

Accurate testing is critical to getting optimal thyroid treatment. Maintenance testing is generally done every six months if you have reached a stable dosage. However, for those who have not yet reached an optimal dose, they can expect to do blood tests about every 30-60 days.

Additional testing may also be required during colder seasons as cold weather can impact thyroid function resulting in a need for increased dosage.

It may seem overwhelming to balance the proper timing of testing in addition to the many tests administered to acquire an accurate assessment of your thyroid. Fortunately, the Holtorf Medical Group can help you better understand the testing process and provide you with everything you need to ensure an accurate and comprehensive diagnosis.

Be sure to follow the medication timing practices applicable to your thyroid treatment to ensure that testing is accurate. By fasting, waiting for the appropriate amount of time after medicating, and testing at regular intervals, you can improve the accuracy of your thyroid lab work.

To learn even more about thyroid function and proper thyroid support, read our Thyroid 101 e-book!


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Holtorf Medical GroupThe Holtorf Medical Group specializes in optimizing quality of life and being medical detectives to uncover the underlying cause of symptoms, rather than just prescribing medications to cover-up the symptoms. We are experts in natural, prescription bioidentical hormone replacement and optimization, complex endocrine dysfunction, fibromyalgia, chronic fatigue syndrome and Lyme disease. We’ve dedicated our practice to providing you the best in evidenced-based, integrative medicine that’s not only safe and effective, but provides measurable results.


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