What You Need To Know About Doing Thyroid Blood Tests (2022)

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Originally published on 30th May 2017Last updated on 23rd December 2019

Common questions about thyroid blood tests for those with medical conditions such as a thyroid disorder include:

  • Do I take my thyroid medication as normal before the blood draw?
  • Do you need to fast for thyroid blood work?
  • How often should it be done?
  • Does it need to be in the morning?
  • Can it be done in the afternoon?
  • Is fasting required for a TSH test?
  • What should be tested?

What You Need To Know About Doing Thyroid Blood Tests (1)

Probably the most important thing to be aware of as someone with a thyroid condition, is whether you should take your thyroid medication before or after having any testing done.

When To Take Medication

T4-Only Meds

In regards to T4-only medication such as Levothyroxine and Synthroid, they only have a half-life of around five to nine days, which means that once you’ve become stable on a dose, it takes around a week for half of that dose to clear the body and blood levels to reflect this. This is why, when some people decide to stop taking it, they feel fine for the first week or so.

Therefore, whether you take T4-only medication right before your blood test or blood sample is taken, or haven’t taken it for up to two days beforehand, your TSH levels and Free T3 levels should still be the same, but free T4 may well show a peak two hours after taking T4 medications.

According to Thyroid Manager:

“Serum T4 (Free T4) concentrations peak twoto four hours after an oral dose and remain above normal for approximately six hours in patients receiving daily replacement therapy.” For this reason, thyroid expert Richard Shames, MDhas the following recommendation: “I absolutely recommend that patients have any morning blood tests evaluating the thyroid before taking any thyroid medication. I have always told my patients to do it this way.”

The American Association of Clinical Endocrinologists and The American Thyroid Associated Guidelines also state:

“In monitoring patients with hypothyroidism on L-thyroxine replacement, blood for assessment of serum free T4 should be collected before dosing because the level will be transiently increased by up to 20% after L-thyroxine administration. In one small study of athyreotic patients, serum total T4 levels increased above baseline by 1 hour and peaked at 2.5 hours, while serum free T4 levels peaked at 3.5 hours and remained higher than baseline for 9 hours.” [1]

(Video) What are your thyroid blood tests really saying?

So, if you were to take your T4-only thyroid medication before a thyroid blood draw, your Free T4 levels could come out elevated, leading to your doctor lowering the medication dosage, when you don’t actually need it lowering.

However, in most cases, taking T4-only medication the morning of your test will not be an issue, as most doctors tend to adjust dosages according to TSH only, which shouldn’t be affected (although this is incorrect. It should be adjusted based on the Free T3 and T4 levels too). Butto get a reading of your Free T4 level that is reflective of most of the day (and something your doctor should also be testing, alongside TSH) you will needto hold fire on taking your medication until after the lab test.

T3 Meds

Now, if you’re taking a thyroid medication that contains T3, such as NDT or T3 synthetic Liothyronine, it’s important to be aware that T3 has a half-life of around eighteen hours.

Straight after taking a T3 containing medication, the TSH level begins to fall and then stays suppressed for as long as five hours. Free T3 levels also increases after taking T3 medication and hit a peak after two and a half hours. [2]

This means that if you were to take your T3 containing thyroid medication within five hours of getting your thyroid tests done, your test results may imply that you are overmedicated when you’re not, or even that your levels are within range or optimal, when you’re actually under-medicated. So it can affect your ability to get an accurate result and adjust your dosage accurately.

Therefore, you’re best to hold off taking this medication until after the blood draw. I take my thyroid medication with me so that I can take it straight after the blood test, otherwise I start to feel unwell by midday.

The bottom line is: you’ll get a more accurate result if you take any thyroid medications after the blood test.

Biotin

If you’re also one of the thyroid patients who take the supplement biotin, it is also worth knowing that it can cause falsely elevated thyroid levels on test results, making you look overmedicated or hyperthyroid when you’re not. Therefore, it is advised to not take it for at least 48-hours before a thyroid blood test.

(Video) Thyroid Blood Tests

Should I Fast for a Thyroid Test?

Do I have to fast for TSH blood work? Do thyroid blood tests require fasting?

In terms of fasting, most doctors tell thyroid patients that it’s not necessary to fast before a blood test. However, researchers have found that after eating, our TSH level becomes suppressed. [2]

This means that a high TSH could instead look much lower after eating, and borderline levels no longer borderline. As so many doctors use the TSH level to decide if a patient is adequately treated, or in need of more or less thyroid medication, this could result in patients having their thyroid medication wrongly altered, or even being told that their ‘borderline’ hypothyroidism is now ‘normal’, resulting in some thyroid patients being inadequately treated for their thyroid condition. All because they ate before their test.

Therefore, your TSH level is likely to be at its highest and most reflective of its underlying status, when tested after fasting, in the early morning.

Timing Matters

Another thing to keep in mind is the time at which your blood is drawn for thyroid testing.

Each time you have your thyroid tests done, you should aim for it to always be done at the same time, and under the same circumstances (i.e. fasting), so they’re as accurate and comparable as possible.

Given that you shouldn’t take your medication until after the draw, as early as possible in the morning and before 9am is preferable. This is because thyroid hormone levels have a circadian rhythm with a peak at night, so Dr. Geracioti suggests that blood tests for hypothyroidism be done before 9am in order to not miss subclinical hypothyroidism and have as accurate results as possible. [4]

Does Being Ill Affect The Test?

Being unwell could affect test results temporarily.Sometimes, infections or a bout of an inflammatory condition can alter results until the illness resolves, so if you receive an unexpected result when unwell, it is probably wise to retest after you’ve recovered to rule it out.

Also, as diarrhoea can interfere with the absorption of your thyroid medication, this could affect your thyroid hormone levels and any testing.

Does Menstruation Affect Testing?

Generally, being on your period when having a thyroid test conducted isn’t known to cause any issues or affect results, but if you’re feeling particularly unwell from your period then you may wish to have blood drawn when you feel better. Especially if you already lose a lot of blood with menstruation. Heavy periods can be a symptom of hypothyroidism.

How Often?

In terms of how often you should be having your thyroid tests conducted, once every six to twelvemonths is standard if your levels are optimal and you feel well. Every two months is more common if you’re still adjusting dosage and having symptoms.

(Video) Thyroid Blood Testing: Everything You Need To Know

Many patients need their dosage altering as the weather gets colder, and again when it warms up, to reflect an increase or decrease in demand for thyroid hormone, due to external temperatures.

When first starting thyroid medication for hypothyroidism, most doctors recommend testing thyroid levels again about four to six weeks after the start of the treatment, to determine if the dose of medication is correct, but waiting eight weeks can allow the medication to finish building in the body and supply a more accurate reading.

When your thyroid gland isn’t working properly, thus leading to hypothyroidism, it’s incredibly important to correct the low levels of thyroid hormone with frequent and thorough testing.

What Should Be Tested?

A full thyroid panel (also known as a thyroid function test) is required to obtain the most comprehensive and accurate look at how you’re doing, as TSH alone and even TSH and Free T4 test without the other components of the thyroid panel, don’t give the full picture.

Free T3 and Thyroid Antibodies TpoAB and TgAB are important to monitor too. Many thyroid patients find that whilst their TSH is OK, their Free T3 and Free T4 are not optimal and so they still feel unwell. If your doctor won’t order the full thyroid panel, do know that it is relatively inexpensive and simple to order these tests yourself. UK thyroid patients can order them fromhereand a worldwide link can be seenhere.

TSH serves as an average read out over the previous four to six weeks of your thyroid levels but doesn’t give the most comprehensive view.

Do you follow these tips when you have blood drawn?

What You Need To Know About Doing Thyroid Blood Tests (2)See also:

The bookBe Your Own Thyroid Advocate: When You’re Sick and Tired of Being Sick and Tired,which builds on this article in detail and explains how to thrive with thyroid disease.

You can click on the hyperlinks in the above article to learn more and see references to information given, as well as the below links.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5167556/

References:

(Video) Thyroid function tests (TFTs) and labs explained in under 7 minutes (ish)

[1] https://in.bgu.ac.il/en/fohs/communityhealth/Family/Documents/HYPOTHYROIDISM%20Guidelines%20ATA%20AACE%202012.pdf

[2] https://www.thyroidmanager.org/chapter/adult-hypothyroidism/#toc-9-8-1-pharmacology-of-thyroid-hormone-replacement-preparations1

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4171896/

[4] http://www.schizophrenia.com/sznews/archives/004348.html#

Like this article? Follow Rachel on Facebook | Instagram | Twitter | Pinterest​ for more great thyroid content.

What You Need To Know About Doing Thyroid Blood Tests (3)

Rachel Hill

Rachel Hill is the highly ranked and multi-award winning thyroid patient advocate, writer, speaker and author behind The Invisible Hypothyroidism. Her thyroid advocacy work includes writing articles, authoring books, producing her Thyroid Family email newsletters and speaking on podcasts, as well as being a founding board member for theAmerican College of Thyroidology. She is well-recognised as a crucial and influential contributor to the thyroid community and has a large social media presence. Her books include “Be Your Own Thyroid Advocate” and “You, Me and Hypothyroidism”.

(Video) Don't make these mistakes before getting Thyroid Blood Test - Dr. Tanvi Mayur Patel

FAQs

How do I prepare for a thyroid blood test? ›

No test preparation is needed. However, certain medications, multivitamins and supplements can interfere with thyroid testing, so tell your healthcare practitioner about any prescribed or over-the-counter drugs and/or supplements that you are taking.

What should I avoid before a thyroid test? ›

The thyroid “takes up” iodine from the blood to make thyroid hormones, which is why this is called an uptake test. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.

Can you eat before a blood test for thyroid? ›

Most doctors will suggest you do not fast before your thyroid function test. Research shows that fasting, especially early in the morning, may impact TSH levels. A fasting test typically results in higher TSH levels versus one done in the afternoon.

What is the best time of day to have a thyroid test? ›

[1] A large laboratory data-based study by Ehrenkranz et al. showed that there is a significant circadian variation in the TSH levels with peak levels occurring between midnight and 8 am and nadir levels between 10 am–3 pm and 9–11pm.

How many hours of fasting is required for thyroid test? ›

Usually,no special precautions including fasting need to be followed before taking a thyroid test. However, your pathologist can guide you better. For example, if you have to undergo some other health tests along with thyroid hormone levels, you may be asked to fast for 8-10 hours.

What medications can affect your thyroid? ›

Which drugs can cause thyroid dysfunction and should this be treated?
  • Amiodarone. Amiodarone can cause transient alterations of thyroid function tests, as well as overt hypothyroidism or hyperthyroidism. ...
  • Lithium. ...
  • Interferons (IFN) ...
  • Tyrosine Kinase Inhibitors (TKIs) ...
  • Alemtuzumab. ...
  • Iodine-containing medications and agents.

What are early warning signs of thyroid problems? ›

7 Early Warning Signs of Thyroid Issues
  • Fatigue.
  • Weight gain.
  • Weight loss.
  • Slowed heart rate.
  • Increased heart rate.
  • Sensitivity to heat.
  • Sensitivity to cold.
11 Jan 2021

Can caffeine affect thyroid test? ›

Caffeine in coffee and other caffeinated beverages can affect the absorption of the thyroid drug levothyroxine by making the drug pass through your gut too quickly. This can cause your T4 hormone levels to drop or fluctuate.

Can I drink water before thyroid test? ›

Can I drink water before Thyroid Test? "Yes, you can have water before a Thyroid Test."

What are the symptoms of an underactive thyroid in females? ›

Symptoms of an underactive thyroid
  • tiredness.
  • being sensitive to cold.
  • weight gain.
  • constipation.
  • depression.
  • slow movements and thoughts.
  • muscle aches and weakness.
  • muscle cramps.

Can stress affect TSH levels? ›

"Stress increases production of the hormone cortisol, which is produced by the adrenal glands. Cortisol can inhibit secretion of TSH (thyroid stimulating hormone) from the pituitary gland, leading to partial suppression of thyroxine, the main hormone produced by the thyroid gland," Dr.

How long does a thyroid blood test take? ›

What happens during a thyroid function test? A thyroid function test is a simple blood test. The blood sample is then sent to the laboratory for analysis and the results are sent back to the doctor who asked for the tests. The results usually take 1-3 days to come back.

How did I get hypothyroidism? ›

The most common cause of hypothyroidism is an autoimmune disorder known as Hashimoto's thyroiditis. Autoimmune disorders occur when your immune system produces antibodies that attack your own tissues. Sometimes this process involves your thyroid gland.

How can I improve my thyroid function? ›

Thyroid Superfoods
  1. Roasted seaweed. Seaweed, such as kelp, nori, and wakame, are naturally rich in iodine--a trace element needed for normal thyroid function. ...
  2. Salted nuts. Brazil nuts, macadamia nuts, and hazelnuts are excellent sources of selenium, which helps support healthy thyroid function. ...
  3. Baked fish. ...
  4. Dairy. ...
  5. Fresh eggs.
11 Jan 2018

Why do you have to drink a full glass of water with levothyroxine? ›

Take the tablets with a full glass of water as they may get stuck in your throat or cause choking or gagging. If you are giving levothyroxine to an infant, child, or adult who cannot swallow the tablet, crush and mix it in 1 to 2 teaspoons (5 to 10 mL) of water.

What is normal TSH level for age? ›

AgeFree T4* (ng/dL)TSH (mU/L)
1 to 5 years0.8 to 1.80.7 to 6.6
6 to 10 years1.0 to 2.10.8 to 6.0
11 to 18 years0.8 to 1.90.6 to 5.8
>18 years0.9 to 2.50.4 to 4.2
4 more rows

What makes thyroid levels fluctuate? ›

For people with thyroid disease, certain things can cause fluctuations in thyroid hormone levels. These may include disease progression, medication changes, other herbs and supplements, and the change of seasons.

Does low TSH cause weight gain? ›

According to Kitahara, if someone has low thyroid function, their TSH is high, and the thyroid hormones known as T3 and T4 are low—and weight gain often occurs. If someone has an overactive thyroid, or hyperthyroidism, TSH is usually low, the T3 and T4 are high, and weight loss occurs.

Can I drink coffee before a fasting blood test for thyroid? ›

Before Your Blood Test

— If you are having a lipid test, do not drink alcohol 48 hours before the test. You may drink normal amounts of water before your test. Do not drink any other liquids. This includes coffee, decaffeinated coffee, tea or juice.

What can mimic hypothyroidism? ›

  • Angioedema.
  • Bronchitis.
  • Bulimia Nervosa.
  • Chronic Obstructive Pulmonary Disease.
  • Congestive Heart Failure.
  • Depression.
  • Menopause.
  • Preeclampsia.

Can I drink water before thyroid test? ›

Can I drink water before Thyroid Test? "Yes, you can have water before a Thyroid Test."

What medications affect thyroid tests? ›

Which drugs can cause thyroid dysfunction and should this be treated?
  • Amiodarone. Amiodarone can cause transient alterations of thyroid function tests, as well as overt hypothyroidism or hyperthyroidism. ...
  • Lithium. ...
  • Interferons (IFN) ...
  • Tyrosine Kinase Inhibitors (TKIs) ...
  • Alemtuzumab. ...
  • Iodine-containing medications and agents.

How long do thyroid blood tests take? ›

What happens during a thyroid function test? A thyroid function test is a simple blood test. The blood sample is then sent to the laboratory for analysis and the results are sent back to the doctor who asked for the tests. The results usually take 1-3 days to come back.

Can I drink coffee before a fasting blood test for thyroid? ›

Before Your Blood Test

— If you are having a lipid test, do not drink alcohol 48 hours before the test. You may drink normal amounts of water before your test. Do not drink any other liquids. This includes coffee, decaffeinated coffee, tea or juice.

What are early warning signs of thyroid problems? ›

7 Early Warning Signs of Thyroid Issues
  • Fatigue.
  • Weight gain.
  • Weight loss.
  • Slowed heart rate.
  • Increased heart rate.
  • Sensitivity to heat.
  • Sensitivity to cold.
11 Jan 2021

Can caffeine affect thyroid test? ›

Caffeine in coffee and other caffeinated beverages can affect the absorption of the thyroid drug levothyroxine by making the drug pass through your gut too quickly. This can cause your T4 hormone levels to drop or fluctuate.

What is normal TSH level for age? ›

AgeFree T4* (ng/dL)TSH (mU/L)
1 to 5 years0.8 to 1.80.7 to 6.6
6 to 10 years1.0 to 2.10.8 to 6.0
11 to 18 years0.8 to 1.90.6 to 5.8
>18 years0.9 to 2.50.4 to 4.2
4 more rows

What vitamin helps thyroid function? ›

Vitamin A. Vitamin A regulates thyroid hormone metabolism and inhibits thyroid-stimulating hormone (TSH). Researchers in a 2017 review highlight the critical role vitamin A plays in thyroid function. For example, deficiency in vitamin A can worsen thyroid disorders that have happened due to iodine deficiency.

Does thyroid affect BP? ›

When the thyroid gland doesn't produce enough thyroid hormone (hypothyroidism) or produces too much thyroid hormone (hyperthyroidism), high blood pressure can result.

What time of day is TSH lowest? ›

[2,3] Circulating TSH shows a normal circadian rhythm with a peak between 11 pm-5 am and a nadir between 5 pm-8 pm.

What are the symptoms of an underactive thyroid in females? ›

Symptoms of an underactive thyroid
  • tiredness.
  • being sensitive to cold.
  • weight gain.
  • constipation.
  • depression.
  • slow movements and thoughts.
  • muscle aches and weakness.
  • muscle cramps.

How much water should you drink before a blood test? ›

Ideally, start drinking more fluids the day before your blood draw, and continue to drink water before you have your blood drawn. Excessive amounts aren't necessary; most sources ecommend that an adult drink 64 ounces of water per day for good health, which is more than adequate for having your blood drawn.

What is a good TSH level for a woman? ›

What is a normal TSH level in a woman? An optimal TSH level in a woman is 0.4-2.5 mIU/L. For pregnant women, that upper limit is stricter than if you are not pregnant. A dangerously high level of TSH is above 5.0 mIU/L.

Videos

1. Thyroid Blood Tests | Thyroid Series | Dr.Ravi Sankar | Endocrinologist | Hi9
(Hi9 Web TV)
2. Thyroid testing: How to get 100% accurate results (how and when to test your thyroid)
(Dr. Westin Childs)
3. Blood tests are all that's needed to detect thyroid disease
(KRIS 6 News)
4. Thyroid function test - Hypo and hyperthyroidism || symptoms & diagnosis
(egpat)
5. What Do Thyroid Lab Tests Really Tell You?
(Datis Kharrazian)
6. QUICK AND SIMPLE HOME THYROID TEST | ARE THEY WORTH IT?
(Chronically Wonderful)

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