Countless patients visit their doctors for their annual physicals with complaints that include fatigue, weight gain, anxiety and more. Their doctors then perform screenings that include thyroid labs, only for the labs to come back “normal.” However, if you are experiencing a list of symptoms that are common thyroid symptoms, there’s a chance that there’s something your doctor has missed.
Some people treated for hypothyroidism may still experience symptoms even if blood tests show that their thyroid stimulating hormone (TSH) levels are well within the normal range. The reasons for this are complex, but the bottom line is that having a normal TSH value doesn’t necessarily mean that all of your symptoms will go away.
Interpreting Thyroid Lab Work Correctly
Many doctors look just at the TSH (thyroid stimulating hormone) levels when they are assessing a patient for a potential thyroid problem. However, TSH levels only begin to expose potential issues. An individual may have normal TSH levels but still not be utilizing thyroid stimulating hormone correctly, leading to a thyroid imbalance.
Your doctor should also be looking at your other values such as T3 and T4 levels. These can provide more information about how well your thyroid is actually functioning.
Additionally, it is important to realize that levels that are sometimes considered “normal” are actually a sign of a thyroid problem. Most doctors consider TSH levels that are between 0.5 and 5.0 normal. However, a patient who is still experiencing a range of thyroid symptoms may be hyperthyroid or hypothyroid. Many thyroid health advocates think that the range that is considered normal should be narrowed significantly so that more people who have thyroid problems can get the treatment they need.
One other value that is extremely important to examine is autoimmune factors. Both Graves’ disease, the most common cause of hyperthyroidism and Hashimoto’s disease, the most common cause of hypothyroidism, are autoimmune. By examining antibody levels, your doctor can learn whether your immune system has put your thyroid under attack. Even if you are not currently showing symptoms that have been connected to your thyroid, an autoimmune issue should be addressed to reduce the chances of long-term harm.
- T4 to T3 Under-Conversion
Many people assume that TSH is a thyroid hormone, but it’s actually not. It is a hormone produced by the pituitary gland, the organ that detects whether thyroid hormone levels in the blood are high or low. If the latter, the pituitary gland will secrete TSH to spur the thyroid gland into action.
The thyroid gland will produce several different hormones. The role of these hormones is to regulate body metabolism (the conversion of oxygen and calories into energy). The main hormone is thyroxine (T4),2 which only has a moderate effect on metabolism.
However, when thyroxine loses a molecule of iodine in a process called monodeiodination, it is converted into triiodothyronine (T3), the “active” thyroid hormone able to exert four times the hormonal strength of T4.
T4 is less active in the body than T3. Most cells in your body cannot utilize T4, which is why T4 is converted in tissues throughout your body into the more active T3. In under-conversion, the conversion of T4 into T3 is impaired, resulting in low thyroid hormone activity throughout the body despite normal TSH and T4 levels. Causes of under-conversion include high cortisol levels, nutritional imbalances, and inflammation. Patients with under-conversion experience hypothyroid symptoms with normal lab results on TSH and T4, but have lower blood levels of T3.
- Elevated Thyroid-Binding Globulin
Along with controlling the release of TSH, another way your body modulates the function of thyroid hormones in your body is with a transport protein called thyroid-binding globulin (TBG). Elevated thyroid-binding globulin can be caused by sex hormone imbalances, like excessive estrogen levels, or by use of oral contraceptives in women.[reference] Patients with elevated TBG will have normal TSH, normal T4, low T3, high T3 uptake, and high TBG test numbers.
- Decreased Thyroid-Binding Globulin
High levels of thyroid-binding globulin are a problem, but low TBG can also cause thyroid issues. Under conditions of decreased TBG, thyroid hormones temporarily become overactive because they aren’t bound to the transport protein. Over time, this overactivity can cause resistance to the effects of thyroid hormone, resulting in hypothyroid symptoms. High levels of testosterone can cause decreased TBG levels.[reference] Low TBG is more common in women with polycystic ovarian syndrome (PCOS) and insulin resistance, each of which can lead to increased testosterone. Patients with decreased TBG levels will have normal TSH, normal T4, high T3 levels.
- Resistance to Thyroid Hormones
In thyroid hormone resistance, thyroid hormone levels (TSH, T4, and T3) are normal, but cellular resistance creates thyroid dysfunction. This thyroid disorder is difficult to pinpoint because it doesn’t show up on tests. An inherited genetic disorder causes some cases of thyroid resistance syndrome.[reference] High body-mass index, acute illness, and chronic stress are also linked to thyroid hormone resistance.[reference][reference]
- Reverse T3
Reverse T3, or rT3 for short, is a hormone that’s structurally similar to T3, but resembles a mirror image of the active T3 molecule. Many cells in your body have thyroid receptors, which are like a lock-and-key system that allows thyroid hormone to act on your cells. At the cellular level, T3 activates the thyroid receptor, while reverse T3 inhibits it. Reverse T3 is one way your body regulates thyroid function to stay in homeostasis, a healthy state of balance. When you are ill, stressed, or starving, your body will begin to convert T4 into reverse T3 instead of active T3. Reverse T3 is your body’s way of putting the brakes on your metabolism to conserve energy and counteract the effects of stress. Some people get “stuck” in a high rT3 state due to chronic illness, stress, or overzealous attempts to lose weight. If you have high rT3, your TSH and T4 levels will be normal, but you will have high rT3 values and may have low levels of T3.
References
https://completecare.net/thyroid-symptoms-with-normal-labs/
https://www.verywellhealth.com/tsh-test-results-normal-symptoms-3233014
