Do’s and Don’ts of Thyroid Lab Testing

Are you curious about thyroid lab testing? Here are the do's and don'ts of getting your labs done. This will help ensure that you get accurate results and can start working on improving your thyroid health!

For measuring Thyroid Level, there are a series of blood tests to know how well your thyroid is working. These tests include T3, T3RU, T4, and TSH. 

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The thyroid is a small gland located in the lower front part of your neck. It is responsible for regulating many bodily processes such as metabolism, energy production, and mood.

The thyroid produces two main hormones: triiodothyronine (T3) and thyroxine (T4). If your thyroid doesn’t produce enough of these hormones, you may experience symptoms such as weight gain, lack of energy, and depression. This condition is called hypothyroidism and when your thyroid produces too many hormones, you may experience weight loss, severe anxiety, tremors, and feeling high. It is called hyperthyroidism.

Thyroid Lab Testing

Usually, a doctor concerned about your thyroid hormone levels will order extensive screening tests, such as T4 or thyroid stimulating hormone (TSH) test. If these results are abnormal, your doctor will order further tests to determine the cause of the problem.

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Do’s and Don’ts of Thyroid Lab Testing

There are various points that you should keep in mind while undertaking Thyroid Tests. These are: 

  1. Before having blood drawn to check your thyroid levels, talk to your doctor about any medications you are taking. Also, tell them if you are pregnant. Certain medications and pregnancy can affect your test results.

Certain medications and pregnancy can affect your test results

  1. You don't need any special preparations for a TSH blood test. If your health care provider has asked for other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.
  2. High TSH levels can mean your thyroid is not making enough thyroid hormone, a condition called hypothyroidism. Low TSH levels can mean your thyroid is producing too much hormone, a condition called hyperthyroidism. A TSH test does not explain why the TSH level is too high or too low. If your test results are abnormal, your doctor will likely order additional tests to determine the cause of your thyroid problem. These tests may include: 
    • T4 thyroid hormone tests optimal range 15-23pmol/L
    • T3 thyroid hormone tests optimal range 5-7 pmol/L
    • Tests to diagnose Graves' disease, an autoimmune disease that causes an overactive thyroid gland 
    • Tests to diagnose Hashimoto's thyroiditis, an autoimmune disease that causes hypothyroidism. 

TSH testing for thyroid


  1. It is recommended that you should take your medication at the same time each day with a glass of water at least 30 minutes before a meal. Avoid taking acid reflux medications and magnesium, calcium, and iron supplements within four hours of taking thyroid medications as they can interfere with the absorption of thyroid medications. 

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  1. Absorption can also be affected by foods such as soybeans, cottonseed, nuts, and dietary fiber. Beverages (other than water) may also impair absorption. It should be noted that coffee can reduce the absorption of T4 in the intestine. Hot water with lemon is an exception however; taking your thyroid medicines with warm lemon water can provide the necessary acidity to aid absorption (and is also great for aiding in liver detoxification).

Foods like nuts affect tests

  1. Getting the best intake of your thyroid medication helps your body get enough thyroid hormone and can improve your results on a laboratory test. In general, if you are only on T4 medication, it is recommended to delay your thyroid medicines until after your lab test. For best results, schedule your thyroid tests early in the morning and bring your thyroid medication to your appointment center for taking it immediately after the lab test.

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  1. To get an accurate reading of your TSH levels on a T3-containing drug you must wait at least 13 hours after taking your T3-containing drug before taking the test. With T3/T4 combination medication, it is recommended to get your thyroid function tests first thing in the morning before taking your medication. Bring your medication with you and take it right after your thyroid tests are complete to ensure that you get accurate lab results.
  2. Certain Supplements may interfere with lab results:
    • Biotin
    • Supplements containing estrogenic compounds,
    • Glucocorticoids, dopamine, dobutamine, and octreotide,
    • Certain no steroidal anti-inflammatory drugs
    • Drug-drug interactions
  3. If after receiving accurate results, you still feel some symptoms then this may involve adjusting dosages, switching to a different medication, or the possibility of something interfering with the absorption of your thyroid medication such as gluten. 

herbal supplements interfere with lab test

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  1. There are certain supplements that can result in a false reading. These include aloe vera, ashwagandha, and vitamin A. 


To conclude getting accurate results is important to ensure no ineffective changes are being made to your current medications and to assess how well your thyroid is functioning. Once you have identified and corrected things that could be affecting your TSH or T4 lab results, you should consider retesting with the appropriate timing of medication and/or supplements to ensure accuracy.



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