Free Thyroxine (T4) test: Things you need to know before getting tested

Quick Bites

  • Thyroxine is a hormone released by the thyroid gland and free thyroxine or free T4 is a part of it
  • Normal levels of free T4 are important for sustaining a pregnancy
  • A free T4 test can provide information about male and female infertility issues



If you are suffering from problems like fertility issues, trouble getting pregnant, fatigue, or any thyroid-related diseases, your doctor may have ordered a free thyroxine (T4) test. If you are wondering what this test does? Let’s first start with the basics of thyroxine, how it affects your body, and how you can prepare yourself before you take the test.

In this article


What is thyroxine hormone?

Thyroxine is one of the main hormones released by the thyroid gland into the bloodstream [1]. The other hormone released from the thyroid gland is T3. T3 is known as triiodothyronine and T4 is known as thyroxine. The hormones released by a thyroid gland (T3 and T4 hormone) play crucial roles in regulating the functions of the body like metabolism, brain development, heart function, maintenance of the bones, and the functions of the reproductive system. Thyroxine (T4 hormone) comes in two forms bound T4 and free T4. [2] The thyroid gland malfunction can cause an imbalance in the production of T3 and T4 hormone causing various reproductive health issues. Some of the fertility issues caused by thyroid gland malfunction are pregnancy loss, ovulatory disorders, irregular periods, and preterm birth.

Read more: Importance of Hysterosalpingography Test (HSG) in Infertility

What is a free thyroxine (T4) test?

As we know, T4 secreted by the thyroid hormone is of two types,

  • Free T4 - It enters the body tissues.
  • Bound T4 - It binds to the protein, making it impossible to enter the body tissue.

A free thyroxine blood test measures the level of free T4 in the blood. The test identifies any problem with thyroid gland functioning. This test is more accurate than the total T4 test (a test used to check levels of both free and bound T4 levels). Free thyroxine test usually performed along with a TSH test to identify thyroid disorder. Thyroid disorder is the second most common endocrine disease to affect women of reproductive age.

A free thyroxine (T4) test is a simple blood test. This test usually takes less than five minutes. The doctor will collect the blood sample from the vein of your arm, with the help of a small needle.

There are no preparations required before the test. You may check-up with your doctor to see if you need to stop eating and drinking a few hours before the test.

Read more:Estradiol (E2) Hormone Test and its effect on fertility

When is a free thyroxine (T4) test recommended?

Abnormal thyroid functions can cause problems with menstruation in females and can cause fertility issues. If you are facing trouble conceiving, your doctor may recommend some tests, and a free thyroxine test could be one of them.

A Free T4 test along with or after other tests like the TSH test -

  • Help find out if you have thyroid conditions like hyperthyroidism and hypothyroidism and their cause
  • To find out what type of thyroid disorder you have like Hashimoto's disease, Graves' disease, goiter, and thyroid nodules
  • To identify the reason for delayed pregnancy
  • To monitor the T4 and TSH levels in people having thyroid cancer.
  • To monitor the effect of thyroid treatment in people undergoing treatment.
  • Help evaluate how the pituitary gland is working [3]
Read more:Importance of Testosterone Hormone Test in Fertility

Normal free thyroxine (T4) Levels in men and women

The levels of free thyroxine (T4) vary according to age, gender, health history, the method used for the test, and other things. The normal levels of free T4 are measured in nanograms per deciliter (ng/dL) or picomoles per liter (pmol/L). Reference ranges for free T4 are given below [4].

In Women

  • In Adult Females: 0.9 to 2.3 ng/dL (12 to 30 pmol/L)
  • In first trimester of pregnancy: 0.8–1.53 ng/dL (12.1 - 19.6 pmol/L)
  • In second trimester of pregnancy: 0.7–1.20 ng/dL (9.6 - 17.0 pmol/L)
  • In third trimester of pregnancy: 0.7–1.20 ng/dL (8.4 - 15.6 pmol/L)

In Male

  • In Adult Male: 0.9 to 2.3 ng/dL (12 to 30 pmol/L)

Your test results may not mean you have any problem with your health. Ask your doctor what your test results mean for you.

Read more:Luteinizing Hormone Test and Its Importance in Fertility

What do the results of a free thyroxine (T4) test reveal?

The results of the free T4 test can indicate various underlying health conditions. High levels of free thyroxine hormone in the blood is a sign of an overactive thyroid, whereas low levels of free T4 hormone a sign of an underactive thyroid gland and its function.[5]

Higher free thyroxine levels may indicate -

  • Hyperthyroidism: The higher level of free T4 hormone indicates hyperthyroidism. Hyperthyroidism is also called overactive thyroid disease in which the thyroid gland releases high levels (more than needed) of hormones [6]
  • Thyroiditis or toxic multinodular goiter
  • The high protein level in the blood
  • High iodine level in the body
  • Too much thyroid replacement medication
  • Trophoblastic disease, a group of rare pregnancy-related tumors in females
  • Increased risk of early miscarriage and premature birth

Lower free thyroxine levels may indicate -

  • Hypothyroidism: The lower level of free T4 level indicates hypothyroidism. Hypothyroidism is also called underactive thyroid disease in which the thyroid gland doesn’t release hormones in enough quantities [7]
  • Dietary issues, such as fasting, malnutrition, or an iodine deficiency in the body
  • Medications that affect protein levels of the body
  • Long term illness
  • Problem-related to the pituitary gland
Read more:Progesterone Test and Its Importance in Female Fertility

How is the low level of free T4 affects your chances of pregnancy

As stated earlier low levels of thyroxine hormones indicate hypothyroidism (underactive thyroid). If you are suffering from hypothyroidism, you may find it difficult to conceive. Hypothyroidism can cause irregular menstrual cycle, problems with ovulation, and luteal phase defects (which can lead to problems with embryo implantation) [8]. Low levels of free T4 can cause either no egg to release during ovulation or an irregular egg release causing a delay in getting pregnant. If you are a male with low levels of free T4 hormone, you may suffer from low semen quality as the low levels may affect sperm motility and sperm volume.

Not only this, but hypothyroidism can also interfere with infertility treatment like IVF and IUI. If not kept under control, it can drastically reduce your chances of pregnancy naturally or with fertility treatments.

The safest and most effective treatment for hypothyroidism is simply taking a thyroid hormone pill (levothyroxine) once a day, preferably in the morning hours. This medication is a pure synthetic form of T4 hormone, made in a laboratory, and is an exact replacement for the T4 that the human thyroid gland normally secretes.

Read more:Prolactin Levels and Its Impact on Your Fertility

Natural remedies for managing free thyroxine (T4) levels at home?

The high or low levels of free thyroxine can be managed with the help of proper medications. However, you can also manage them by following a specific lifestyle depending upon your low or high free t4 levels.

Natural remedies for managing low free T4 levels:

  • It has been seen in many studies that regular acupuncture can balance thyroid hormone levels. Hence you can introduce acupuncture in our routine for managing your low T4 levels.
  • Selenium is known to balance the levels of T4 levels. You can include selenium-rich foods like whole-wheat bread, beef, chicken, brown eggs, brown rice, sunflower seeds, mushroom, oatmeal, spinach, banana, etc.
  • You can also follow a sugar-free diet. A sugar-free diet will also help with balancing your T4 levels. Instead of going sugar-free, you may also switch to sugar supplements however, sugar supplements may cause other side effects to your body.

Natural remedies for managing high free T4 levels:

  • Many studies have found that consumption of a dietary fiber called glucomannan can lower the levels of thyroid hormones. You can find glucomannan supplements in the form of tablets, capsules, and powder online and pharmacies.
  • In order to manage lower high free T4 levels, you can also avoid taking iodine. Try avoiding iodine-rich food like iodized salt, seafood, high amount of poultry and beef, egg yolks, pasta, pastries, bread, etc.
  • Zinc can help regulate free T4 levels. You can include zinc-rich food like pumpkin seeds, beef, chickpeas, cocoa powder, cashews, lamb, mushrooms, etc in your daily diet.

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List of ReferencesHide

1 . “Thyroxine”., 05 August 2020.

2 . “Thyroxine (T4) Test”., 31 July 2020.

3 . “T4, Free”., 31 January 2020.

4 .

Almomin AMS, Mansour AA, Sharief M. “Trimester-Specific Reference Intervals of Thyroid Function Testing in Pregnant Women from Basrah, Iraq Using Electrochemiluminescent Immunoassay”. Diseases. 2016;4(2):20. Published 2016 Apr 26, PMID: 28933400.

5 .

Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. “Understanding thyroid tests”. 2011 May 24 [Updated 2018 Apr 30]

6 .

Simone De Leo, Sun Y Lee, et al. “Hyperthyroidism”. Lancet. 2016 Aug 27; 388(10047): 906–918, PMID: 27038492.

7 .

Layal Chaker, Antonio C Bianco, et al. “Hypothyroidism”. Lancet. 2017 Sep 23; 390(10101): 1550–1562, PMID: 28336049.

8 .

Indu Verma, Renuka Sood, et al. “Prevalence of hypothyroidism in infertile women and evaluation of response of treatment for hypothyroidism on infertility”. Int J Appl Basic Med Res. 2012 Jan-Jun; 2(1): 17–19, PMID: 23776802.

Last updated on: : 28 Sep 2020

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