How to Interpret Thyroid Tests: Key Points to Understanding your Thyroid Function
Updated: Jan 30, 2019
Over the years, countless patients have told me “my doctor says my TSH is normal, why I still feel like I have a thyroid problem?” I can absolutely relate to the way my patients feel as this is exactly what happened to me. My thyroid test looked “normal” despite my symptoms.
There are multiple blood tests to check when looking at thyroid function. However, in North America, the primary (and often the only test) that is checked is known as Thyroid Stimulating Hormone, otherwise known as TSH.
This test is the basic, standard test to address thyroid function. When you have LOW, or UNDER-ACTIVE thyroid function, your body should make MORE of the hormone TSH. The body increases the amount of TSH as a way to try and increase the hormones T3 and T4 in the body, encouraging hormonal balance.
If your thyroid is healthy, it should produce normal and sufficient amounts of T3 and T4 hormones. If you want to know more about the T3 and T4 thyroid tests, read my blog here.
When your body is operating in hormone balance, and your thyroid is making the appropriate amount of T3 and T4 hormones, the value of TSH reflects this equilibrium. As I have mentioned in many previous blog posts, T4 is the INACTIVE version of the thyroid hormone. It is essentially secreted by the thyroid gland, but then waits around to be converted to the ACTIVE T3 hormone. This T3 hormone is the molecule that allows for weight loss, energy and warm body temperatures.
Hashimoto’s Thyroiditis is the most common cause of hypothyroidism in the United States. It is an autoimmune disorder in which antibodies directed against the thyroid gland lead to chronic inflammation. Most commonly, the body produces Thyroid Peroxidase Antibodies (TPO), causing reduced thyroid function overtime. This condition develops slowly, and often TPO antibodies can be detected long before the change happens in TSH, T3 and T4 hormones.
On the other hand, OVERACTIVE thyroid disease, or hyperthyroidism (also, most commonly develops due to autoimmune disease known as Graves’ disease) causes TSH to increase. The thyroid stimulating hormone becomes reduced because the thyroid is producing too much T3 and T4 hormones. If the patient has Graves’ Disease, then Thyroid Receptor Antibodies (TRAb) will also be elevated.
Conventional Medicine recognizes thyroid dysfunction by the following criteria:
Under-active Thyroid Function
Overt Hypothyroidism: TSH levels are high (typically above 5 or 10 mIU/L)* and T3 and T4 levels are BELOW the normal values
Subclinical Hypothyroidism: TSH levels are high, above 5mIU/L* but T3 and T4 levels are in the normal range.
Overt Hashimoto’s Thyroiditis: Elevated serum TSH with low thyroid hormone (T4) levels plus positive antibodies against TPO (TPOab)
Early detection of Hashimoto’s Thyroiditis: Mild elevation of serum TSH is seen, with normal levels of T4 and positive TPO antibodies (TPOab).
*The normal range for TSH is debated. Most labs in Canada and the US report that the upper limit of TSH is 5mIU/L however, evidence favors the normal range for TSH to actually be 0.3-2.5mIU/L.
Overactive Thyroid Function
Elevation in T4 level accompanied by a low TSH levels.
Graves’ Disease: Elevation in T4 level accompanied by a low TSH level. Patients with Graves' disease often have positive anti–thyroid receptor antibody (TRAb)
As mentioned above, although conventional or standard reference ranges are how medical professionals typically interpret blood work, Functional Medical Practitioners and Naturopathic Doctors often look at thyroid tests through the lens of “optimal reference ranges” IF THE PATIENT IS SYMPTOMATIC.
The chart below outlines standard reference ranges and optimal reference ranges.
(Adapted from Dr. Izabella Wentz PharmD)
Referring to the chart above, if a patient was presenting with cold hands and feet, unexplained weight gain and constipation and had the following blood tests: TSH of 5 IU/L, Free T4 was 9 pmol/L and TPO antibodies was 50IU/L, conventional medicine would typically not treat this patient, even though the diagnosis should really be early detection of Hashimoto’s hypothyroidism. From a conventional medicine perspective, there is not much that can be done by slightly elevated antibodies, even though TSH is on the upper end and T4 is on the lower end. This is because there is currently no medication to reduce TPO antibodies, and the patient would not necessarily qualify for thyroid replacement medication such as synthroid or eltroxin (Levothyroxine).
From a functional or Naturopathic Medicine perspective, there are many preventative measures that could be implemented to help improve thyroid function and reduce antibodies. This would be especially important if the patient had symptoms of low functioning thyroid.
Interpreting reference ranges and symptoms is a science and an art and takes a medical practitioner that is willing to listen to your complaints and take time to look over your lab results.
If you have been struggling with symptoms of thyroid disease, and have only had the TSH blood test ran, it may be helpful to have other thyroid blood tests collected, especially if your TSH does not fall into the “optimal reference range”.