Free Thyroxine

High fT4 levels might mean that your thyroid gland is working too hard, which could be due to a variety of reasons. One possibility is an autoimmune condition called Graves' disease, where your body's immune system accidentally attacks your thyroid, making it produce more hormones than needed. Another reason could be a growth on your thyroid, like a nodule or goiter, which can cause it to make too many hormones. Sometimes, medications used to treat low thyroid function, such as levothyroxine, can lead to high fT4 levels if the dose is too much. Lastly, high fT4 levels could be a sign of thyroiditis, which is when your thyroid gets inflamed and releases stored hormones into your bloodstream. Keep in mind that these are just potential causes, and the exact reason can be different for each person.

Symptoms of high levels of fT4 could include increased heart rate, anxiety, weight loss, difficulty sleeping, and feeling hot or sweaty.

Low fT4 levels might mean that your thyroid gland isn't making enough of this important hormone. This can happen for various reasons, such as stress, not getting enough nutrients, or your body's immune system being out of balance. Some medications, like cholesterol or seizure drugs, could also affect how much fT4 your body makes. Conditions that might cause low fT4 levels include hypothyroidism, where your thyroid gland doesn't make enough hormones, or Hashimoto's disease, which is when your immune system attacks your thyroid gland and causes inflammation.

Symptoms of low levels of fT4 may include fatigue, weight gain, feeling cold, dry skin, depression, and memory problems.