Thyroid-Stimulating Hormone (TSH) (serum)
Thyroid stimulating hormone (TSH) is produced and secreted by the pituitary gland and stimulates the thyroid to make T3 and T4. Increased TSH levels may indicate low thyroid function (Chakera 2012). When TSH is low, it may indicate high thyroid function (Girgis 2011). TSH is used as a first-line screening tool to assess thyroid disease; however, by itself it is insufficient, and needs to be evaluated in conjunction with other thyroid markers such as T3, T4, thyroid antibodies, and other tests (Iddah 2013; Ross 1989; Toft 2003).
- Reference Range: 0.450-4.50 µIU/mL
- LE’s Optimal Range: 1-2 µIU/mL
Free Tri-Iodothyronine (T3) (serum)
This test measures the amount of T3 available to the tissues, or free T3 (Sapin 2003). Many doctors believe that evaluating levels of free T3 is the best indicator of thyroid function (DeGroot 2016). Hypothyroidism is a condition where T3 blood levels are often (but not always) low (Koulouri 2013). This causes cellular dysfunction and metabolic disturbances (Sanyal 2016; Harper 2008; Brent 2012). Symptoms may include weight gain, constipation, dry skin, and hair loss. Hypothyroidism can lead to the development of chronic diseases, such as heart disease, and increases the risk of diabetes (Gronich 2015; Rodondi 2010; Chaker 2016).
- Reference Range: 2.0-4.4 pg/mL (over 19 years)
- LE’s Optimal Range: 3.4-4.2 pg/mL
Total Thyroxine (T4) (serum)
T4 is a hormone produced and secreted by the thyroid gland. At the tissue level, T4 is converted into the more active form of T3. For this reason, T4 is considered a measurement of total production of thyroid hormone. T4 blood levels are low in hypothyroidism, but may also be in the normal range (Chakera 2012). This causes cellular dysfunction and metabolic breakdown. Symptoms of hypothyroidism may include weight gain, constipation, dry skin, and hair loss. Low T4 levels may even lead to the development of chronic diseases such as heart disease and diabetes. T4 blood levels are elevated in hyperthyroidism, but may also be in the normal range or even low (Obuobie 2003; Santos Palacios 2012; Nygaard 2008). Symptoms of hyperthyroidism may include anxiety, insomnia, an increased heart rate, and bowel discomfort.
- Reference Range: 4.5-12.0 µg/dL
- LE’s Optimal Range:
- Women (<60 yrs.) 9-11 µg/dL
- Women (>60 yrs.) 8.5-10.7 µg/dL
- Men 8.5-10.5 µg/dL
Free T4 (serum)
Proteins bind to T4 and carry it throughout the bloodstream. Once in the tissues, T4 is released from the proteins and free to convert into the more active form called T3. For this reason, many doctors believe that measuring free T4 is a good test for thyroid hormone production (Li 2014).
- Reference Range: 0.82-1.77 ng/dL (over 19 years)
- LE’s Optimal Range: 1.46-1.77 ng/dL