What Is the Ideal Range for TSH?

I (a 35-year-old female) have Hashimoto’s thyroiditis. When my TSH gets too high (even when it’s within normal range), I start feeling fatigued and my joint pain increases (I also have rheumatoid arthritis). Is there an ideal TSH? Should I push for a certain range beyond just the standard normal?

—Anonymous

You are not alone in feeling this way. Many of my patients report feeling crummy if their TSH rises too high, meaning they do not have enough thyroid hormone. As someone with Hashimoto’s hypothyroidism myself, I feel the same way.

Let’s review what TSH is and why it is rising. TSH is thyroid-stimulating hormone, a hormone produced in the pituitary gland. Its main effect is to stimulate the thyroid gland to make and release thyroid hormone. If there is too much thyroid hormone in your body, your pituitary gland will stop making TSH. If there is too little thyroid hormone in your body, your pituitary gland will start making more TSH.

The normal range for TSH is large — the American Thyroid Association designates a normal range from 0.4 microunits per milliliter (mcU/mL) to 4.0 mcU/mL. The guidelines suggest that you do not need to start treating a patient for hypothyroidism in many cases until TSH rises to 10 mcU/mL or even 20 mcU/mL! However, once we start treating you for hypothyroidism, the goal is not just to keep the TSH in the normal range.

The guidelines for treating hypothyroidism say that the goals of treatment should be to normalize the TSH and thyroid hormone levels, while taking into consideration the patient’s symptom management, but not overtreating the patient.

In my practice I apply this by considering the TSH level and the patient’s symptoms. If your TSH is 3.9 mcU/mL but you feel great, then there is no need to make a change (unless you are planning a pregnancy, in which case the goal for TSH is 2.5 mcU/mL or less). If your TSH is 3.9 mcU/mL and you are feeling tired and foggy, and you are bloated and constipated, it may be worth adjusting the dose of your thyroid medication to see if you feel better as long as this doesn’t result in a TSH that is too low.

The takeaway: It is not unusual for women with hypothyroidism to feel their best when their TSH is at the lower end of the normal range. The treatment guidelines suggest that if the TSH is high-normal and the patient is symptomatic, it is reasonable to adjust their dose of thyroid hormone as long as that adjustment doesn’t cause the TSH to be too low.