TSH and T4 levels alone are unreliable markers of tissue thyroid levels. Many individuals who report symptoms associated with hypothyroidism have normal TSH and T4 levels. These hormones are even less dependable indicators in the elderly and in cases of illness, inflammation, chronic emotional or physical stress, depression, or dieting. Conducting a comprehensive set of thyroid tests improves accuracy in determining which patients will respond favorably to thyroid supplementation Treatment with T4 preparations alone is frequently ineffective for conditions associated with reduction in T4 to T3 conversion, or in the T4 uptake, or when T4 to reverse T3 (RT3) conversion is increased. This is largely because individuals with conditions impacting health, such as those listed above, have reduced T4 to T3 conversion, and their T4 is converted preferentially to RT3, which functions as a competitive inhibitor of T3, blocking T3 at its receptor. It reduces metabolism, suppresses T4 to T3 conversion, and blocks T4 and T3 uptake into the cell. Despite the unreliability of TSH to indicate global tissue thyroid effect, even slightly elevated TSH (higher than 2) reveals decreased intra-pituitary T3. Exceptions exist, such as tumors secreting TSH. Even patients intensively tested for thyroid disease can have TSH lower than the 2 to 2.5 range. Because pituitary T3 is normally significantly higher than in the remainder of the body, this decrease in pituitary T3 indicates underactive thyroid. Therefore, treatment is probably advisable for individuals with TSH above 2. In a group of people with the same TSH level, a large percentage may actually have reduced thyroid activity. This is because many people secrete TSH that is less bioactive. TSH assays used in clinical practice do not detect this reduction, thereby limiting the usefulness of TSH levels to evaluate thyroid status. Thyroid supplementation should be considered for symptomatic patients who have normal TSH, but have higher than average RT3 and lower than average free T3. To most accurately evaluate the status of a patient’s overall thyroid function, assess serum levels of TSH; free T3; reverse T3; ratios of free T3 and RT3; free T4; anti-TPO antibody; antithyroglobulin antibody; and SHBG, perform clinical assessment, and measure basal metabolic rate and reflex speed. Consider ordering the Thyroid Complete package from www.HealthOneLabs.com tests to determine thyroid function:
- TSH, T3 Uptake, T3, Free T3, Thyroxine (T4), Free Thyroxine Index and Free T4.
- 1) antithyroglobulin antibody and 2) thyroid peroxidase (TPO) antibodies.
- Reverse T3 (RT3 or REVT3), a biologically inactive form of T3.