Why Most Thyroid Patients Are Undertreated
The conventional approach to thyroid disease — test TSH, prescribe levothyroxine if it’s elevated, and call it done — leaves millions of patients with persistent symptoms and sub-optimal function. As a practitioner committed to optimization, understanding the full thyroid axis and applying a more nuanced approach dramatically improves patient outcomes and positions you as a trusted expert in this space.
The Full Thyroid Axis
TSH is produced by the pituitary and signals the thyroid to produce T4 (thyroxine). T4 is then converted peripherally (primarily in the liver and gut) to the active form, T3 (triiodothyronine). Poor conversion — often caused by nutrient deficiencies, chronic stress, inflammation, or gut dysfunction — can result in low T3 despite normal T4 and TSH. This is the functional thyroid dysfunction that standard testing misses.
Comprehensive Thyroid Lab Panel
A complete thyroid workup includes: TSH, free T4, free T3, reverse T3 (rT3), thyroid peroxidase antibodies (TPO), and thyroglobulin antibodies (TgAb). The rT3:T3 ratio is particularly useful — elevated rT3 (often driven by cortisol) competes with active T3 at receptor sites and creates a functional hypothyroid state. TPO and TgAb identify autoimmune thyroid disease (Hashimoto’s) even when TSH is normal.
T3:Reverse T3 Ratio
A free T3 to reverse T3 ratio below 20 (when T3 is in pg/mL and rT3 is in ng/dL) suggests impaired T3 activity at the cellular level. This pattern is common in patients with chronic stress, adrenal dysfunction, or caloric restriction — and it explains why they feel hypothyroid despite a normal TSH.
When to Use T3 Alongside T4
Some patients do not adequately convert T4 to T3 regardless of optimal T4 levels. These patients often respond dramatically to the addition of liothyronine (T3) or a switch to desiccated thyroid extract (DTE), which contains both T4 and T3 in a physiologic ratio. This is a clinical decision based on persistent symptoms, low free T3, and elevated rT3 despite adequate T4 replacement.
Hashimoto’s: The Autoimmune Consideration
Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the developed world. It requires additional clinical attention: identifying and addressing triggers (gluten, infections, gut permeability), selenium supplementation (which reduces TPO antibodies), stress management, and periodic monitoring of antibody levels. Patients with Hashimoto’s often have other autoimmune conditions and benefit from a more comprehensive evaluation.
Monitoring and Adjustment
When using T3-containing therapies, monitor free T3 (target: upper third of reference range), heart rate, temperature, and symptoms closely. T3 has a shorter half-life and requires consistent dosing. Titrate slowly and educate patients that optimization takes time and patience.