Thyroxine (T4) Lab Values

Hi there. My name’s Abby and I’m with nursing.com. In this lesson, we’ll discuss thyroxine, otherwise known as T4. It’s a thyroid hormone. We’ll talk about its normal value, and times when it might be increased or decreased. Let’s get started! 

Thyroxine, or T4, is evaluated or drawn to look at the function of the thyroid gland. It’s one of the thyroid hormones. It’s actually a prohormone to T3, the other thyroid hormone, and conversion is required for the T4 to actually be active in the tissues. So, there are tons of tissues and glands, organs throughout the body that actually convert T4 to T3, so that it can be effective to the tissues. It helps to contribute to metabolism, muscle control, cardiac function, brain development, and bone maintenance. It’s even good for hair and skin, she’s happy, and nails, beautiful nails. 

Some clinical indications for why we would take this lab are to look at hyper and hypothyroidism. 

It can be used for diagnosis, to evaluate function and to monitor therapy. We’ll also have this lab drawn or see it drawn in the case of hypopituitarism, because what does the pituitary gland produce? TSH, and what does TSH do? It stimulates our thyroid to produce T3 and T4. So, help us in clinical evaluation. 

Normal therapeutic values are between 5 and 12 micrograms per deciliter. This, uh, blood test will be collected in a serum separator tube, a gold top like this one. When lab values are increased for T4, that means likely there’s hypothyroidism, hyperthyroidism, excuse me, like graves’ disease, or there could be nodules, inflammation, right? And certain medications can even increase T4 like birth control, methadone and even some types of hormone replacement, like estrogen. In rare instances, but it is noted, there will also be a raised T4 value in gonadal cancers, or tumors like testicular or ovarian tumors. And it can also be increased, this would be quite acute, in the administration of contrast dye. If someone’s kidneys aren’t doing great, it could affect their values. Now, when it’s decreased, T4, that’s going to indicate hypothyroidism or an underactive thyroid. That thyroid isn’t producing as much of the T4, and that’s why the value is low. We see this in Hashimoto’s disease, it could also be an indication of malnutrition and certain medications. Amiodarone for rhythm issues, hormone replacement for androgens, or a lack thereof, it could also be in the face of lithium. Lithium actually affects our thyroid function. Also, in times of use of anabolic steroids, phenytoin, and propranolol. 

Thyroxine, or T4, is one of the thyroid hormones. It contributes largely to metabolism and functionality of mini body systems. It’s measured to evaluate thyroid function and recall, it’s inactive until it gets converted into T3. Normal values are between 5 and 12 micrograms per deciliter. When values are increased, we’ve got too much, we’ve got hyperthyroidism. When they’re decreased, there’s too little, that’s hypothyroidism. 

Now that wraps it up on our lesson for thyroxine or T4. You all did great. Remember, we know you can do it. Now, go out, be your best self today and as always, happy. Nursing.

References:

• https://medlineplus.gov/lab-tests/thyroxine-t4-test/#:~:text=This%20test%20measures%20the%20level,body%20tissues%20where%20it’s%20needed
• https://www.mountsinai.org/health-library/tests/free-t4-test
• https://www.mountsinai.org/health-library/tests/t3-test
• https://www.uptodate.com/contents/thyroid-hormone-synthesis-and-physiology?search=Triiodothyronine&sectionRank=1&usage_type=default&anchor=H15&source=machineLearning&selectedTitle=1~123&display_rank=1#H15
• https://www.endocrine.org/patient-engagement/endocrine-library/hormones-and-endocrine-function/thyroid-and-parathyroid-hormones
• https://www.aafp.org/afp/recommendations/viewRecommendation.htm?recommendationId=142