Free Triiodothyronine

High fT3 levels might mean that your thyroid gland is working too hard, which is often called hyperthyroidism. This can happen for different reasons, like having an autoimmune disorder such as Graves' disease, inflammation in the thyroid gland, or taking certain medications. When your thyroid gland is overactive, it makes more T3 than your body needs, which can cause your metabolism to speed up and affect how your body functions. Sometimes, high fT3 levels can also be caused by consuming too much iodine, a mineral that's important for making thyroid hormones. Keep in mind that the exact cause can be different for each person.

Symptoms of high levels of fT3 may include rapid heart rate, weight loss, increased appetite, anxiety, irritability, tremors in the hands and fingers, sweating, changes in menstrual patterns, and sensitivity to heat.

Low fT3 levels might mean that your thyroid gland isn't making enough of this important hormone. This could be due to various reasons, such as stress, not getting enough nutrients, or taking certain medications that can mess with how your thyroid works. It could also point to a condition called hypothyroidism, where your thyroid isn't as active as it should be. This can lead to a slower metabolism, which can impact different parts of your body, like your energy levels and heart rate. Keep in mind that everyone's situation is unique, and there could be other factors causing your low fT3 levels.

Symptoms of low levels of fT3 may include fatigue, weight gain, feeling cold, dry skin, hair loss, and slowed heart rate.