Our Approach to Thyroid Hormone Therapy

Our Approach to Thyroid Health

At Modern Age we use different laboratory thresholds for prescribing thyroid therapy. We believe thyroid function is foundational to overall health, and therefore merits proper attention for patients wishing to optimize their health. Our approach to interpreting TSH, free T3 and T4 differs from the way most endocrinologists do (the standard of care).The conventional reference ranges for thyroid hormones like TSH, T4, and T3 are based on statistical distributions in the general population. However, multiple studies show that many people feel unwell and show symptoms of hypothyroidism even when their lab results fall within the normal reference ranges (Wartofsky & Dickey, Hoang et al., Peterson et al.).

For example, the common upper limit for TSH is around 4-5 mIU/L, but research indicates that many patients experience hypothyroid symptoms with TSH between 2-4 mIU/L. Patients with TSH in this reduced range often show improvements in symptoms, body temperature, and cholesterol with T4 treatment (Wartofsky & Dickey, Peterson et al.). Given these studies, we recommend treating patients with TSH above 2 or 2.5 mIU/L rather than waiting until it rises above 4-5 mIU/L (Wartofsky & Dickey, Hoang et al.).

Very often T4 is often measured in isolation without concurrent measurement of T3 levels. T3 reflects the active form of thyroid hormone used by tissue. For free T3, the typical lower limit of the reference range is around 2.3-2.5 pg/mL. However, research indicates the optimal free T3 level is closer to 3.0-3.2 pg/mL. Levels below this are associated with hypothyroid symptoms that improve with T3 treatment, even if the free T3 is still within the conventional normal range (Hoang et al., Peterson et al.).Furthermore, multiple studies show that patients may still have tissue hypothyroidism and low T3 levels even when their free T4 is in the normal range (Peterson et al., Hoang et al.), which means that the panels undertaken by many physicians may overlook thyroid deficiency.

The limitations of the conventional reference ranges reflect the fact that they fail to account for individual variations in thyroid hormone transport, conversion, receptor sensitivity, and physiological needs (Wartofsky & Dickey, Hoang et al., Peterson et al.). Genetics, medical conditions, stress, hormones, and other factors can all affect an individual's optimal thyroid levels. Given this, we advocate for more personalized reference ranges based on comprehensive symptoms and clinical factors rather than just population statistics (Wartofsky & Dickey, Hoang et al.).

In summary, multiple studies demonstrate that tighter reference ranges for TSH, free T4, and free T3 better identify patients who need thyroid hormone treatment to relieve hypothyroid symptoms. This research highlights the inadequacies of the conventional lab ranges for determining individual thyroid status. Experts recommend interpreting lab results in conjunction with the patient's clinical presentation rather than relying solely on whether their results fall inside or outside the standard reference range. An individualized approach allows clinicians to better determine whether thyroid dysfunction could be contributing to the patient's symptoms.

References:

Wartofsky, L., & Dickey, R. A. (2005). The evidence for a narrower thyrotropin reference range is compelling. The Journal of Clinical Endocrinology & Metabolism, 90(9), 5483-5488.

Hoang, T. D., Olsen, C. H., Mai, V. Q., Clyde, P. W., & Shakir, M. K. M. (2013). Desiccated thyroid extract compared with levothyroxine in the treatment of hypothyroidism: a randomized, double-blind, crossover study. The Journal of Clinical Endocrinology & Metabolism, 98(5), 1982-1990.

Peterson, S. J., Cappola, A. R., Castro, M. R., Dayan, C. M., Farwell, A. P., Hennessey, J. V., ... & Jonklaas, J. (2014). An online survey of hypothyroid patients demonstrates prominent dissatisfaction. Thyroid, 24(4), 707-721.