Medically reviewed by Dr. Robert Rubin, MD. Last reviewed November 2026.
If you are experiencing common symptoms of Hashimoto’s despite "normal" labs, you need a more thorough evaluation. A normal TSH level means the pituitary is satisfied. It says nothing about whether the thyroid is converting that output into usable hormone, or whether the immune system is attacking thyroid tissue. Hashimoto's thyroiditis is not primarily a thyroid disorder. It is an autoimmune condition in which the immune system generates antibodies against thyroid tissue. Without testing TPO-Ab and TgAb, physicians and patients have no idea whether an autoimmune process is active. Our Functional Medicine consultation includes a comprehensive thyroid panel as part of initial evaluation, including tests like Free T3, Free T4, Reverse T3, Reverse T3/Free T3 Ratio, TPO-Ab, TgAb, as well as testing for inflammation and nutrient deficiencies. A whole-person centered approach including dietary intervention, improving gut health, reducing inflammatory load, proper sleep, stress relief, and more, is essential — not just thyroid hormone replacement.
This is a scenario every Hashimoto's patient knows well. Your laboratory testing comes back, your doctor tells you everything looks fine, but your symptoms persist: hair loss, weight gain, brain fog. You’ve long suspected you have Hashimoto’s, your symptoms tick all the boxes, but your visit ends with no answers.
You feel like you’ve failed to communicate what you’re experiencing, but it’s not your failure. It’s a failure of the TSH test to capture the full picture. TSH measures one narrow signal in a much more complex system, and for Hashimoto's specifically, it misses the most important information entirely.
TSH (thyroid-stimulating hormone) is produced by the pituitary gland, not the thyroid. It's an upstream signal — the pituitary's instruction to the thyroid to produce more hormone.
In the medical field, the "normal" range itself is contested. Conventional labs typically accept anything between 0.5 and 4.5 mIU/L. Many patients with Hashimoto's experience significant symptoms at the higher end of that range. Functional medicine providers often work toward an optimal range of 1.0 to 2.0 mIU/L — a meaningful difference in how people feel day to day.
A normal TSH level means the pituitary is satisfied. It says nothing about whether the thyroid is converting that output into usable hormone, or whether the immune system is attacking thyroid tissue.
This is the core issue: Hashimoto's thyroiditis is not primarily a thyroid disorder. It is an autoimmune condition in which the immune system generates antibodies against thyroid tissue. TPO (thyroid peroxidase) antibodies and thyroglobulin antibodies can be elevated for years before TSH shifts at all. A patient with perfectly normal TSH can have aggressive antibody activity silently damaging the thyroid.
Without testing TPO-Ab and TgAb, physicians and patients have no idea whether an autoimmune process is active. That matters for treatment. Lowering antibodies is a distinct therapeutic goal from simply normalizing TSH. And it requires a different approach — dietary intervention, gut health, reducing inflammatory load — not just thyroid hormone replacement.
At Improving Your Health, located in Naples and Tampa, we take a Functional Medicine approach to thyroid health that is designed to correct underlying cause(s) of chronic conditions or symptoms. Dr. Rubin is an experienced Functional Medicine physician who has successfully treated hypothyroidism and Hashimoto’s disease in his patients.
Our program begins with a comprehensive functional evaluation before arriving at any diagnosis or recommending any treatment or medication. We look at metabolic markers, hormone levels, body composition and lifestyle factors that influence how well any treatment works for a given patient. Functional medicine consultations include a comprehensive thyroid panel as part of our evaluation.
Test: Thyroid Stimulating Hormone (TSH) test
What it measures: The amount of Thyroid Stimulating Hormone in your bloodstream, which is a hormone produced by the pituitary gland—not the thyroid itself—that serves as a primary indicator of overall thyroid function.
Why it matters in Hashimoto's: TSH acts as a baseline indicator of how well your thyroid is functioning and whether the thyroid is being under- or overdriven. High TSH levels show the pituitary gland is triggering an underactive thyroid to produce more hormone. When blood levels of thyroid hormones drop, the pituitary gland releases TSH to signal the thyroid to increase production. Once hormone levels normalize, a negative feedback loop prompts the pituitary to lower TSH secretion.
Test: Free T4
What it measures: It measures the amount of free thyroxine circulating in your bloodstream, evaluating the "free" or unbound portion of the hormone, which is readily available for your tissues to use, rather than the total T4 that is bound to blood proteins.
Why it matters in Hashimoto's: Monitoring Free T4 is critical because it tells clinicians exactly how much active hormone is available to the body and whether the thyroid is producing adequate output. T4 is considered a storage hormone because it must be converted into T3 by your organs to become active.
Test: Free T3
What it measures: The Free T3 test measures the unbound, metabolically active form of triiodothyronine circulating in your bloodstream.
Why it matters in Hashimoto's: Because Free T3 is the active hormone that drives your cellular energy, tracking it provides a clearer picture of actual tissue thyroid status than simply checking TSH or T4. Even if other markers appear normal, low Free T3 can indicate whether T4 is converting to usable T3 and may explain why a person still struggles with symptoms.
Test: Reverse T3 (rT3)
What it measures: This test measures the amount of reverse T3, the amount of inactive thyroid hormone byproduct circulating in your blood created during T4 conversion. It’s also a measure of conversion stress, levels that rise during physical illness or stress.
Why it matters in Hashimoto's: Reverse T3 can block active Free T3 at cellular receptor sites. High levels can trigger hypothyroid symptoms even when standard blood tests look normal.
Test: TPO antibodies (TPO-Ab) also known as Anti-Thyroid Peroxidase or Thyroid Peroxidase Antibodies
What it measures: The test detects immune system proteins (antibodies) that mistakenly attack thyroid peroxidase, an enzyme essential for producing thyroid hormones.
Why it matters in Hashimoto's: It confirms autoimmune activity and is highly elevated in approximately 95 percent of Hashimoto's cases, acting as the primary marker to diagnose the condition before hormone levels even become abnormal.
Test: Thyroglobulin antibodies (TgAb)
What it measures: It measures the level of autoantibodies in your blood that mistakenly target and attack thyroglobulin, a key protein the thyroid gland uses to produce thyroid hormones.
Why it matters in Hashimoto's: Elevated TgAb levels indicate an active autoimmune attack and inflammation within the thyroid. Finding these antibodies helps doctors confirm a diagnosis of Hashimoto's, thus distinguishing it from non-autoimmune causes of hypothyroidism. While TPO-Ab is the primary test used to identify Hashimoto’s, some patients with autoimmune thyroid issues test negative or borderline for TPO-Ab but positive for TgAb. So, this test serves as a second antibody marker that is important when TPO-Ab is borderline, ensuring an autoimmune response isn't missed.
Test: Free T3/Reverse T3 ratio
What it measures: A Free T3/Reverse T3 ratio is not measured by a test but is instead calculated using results from two separate blood tests: a Free T3 (FT3) test and a Reverse T3 (rT3) test, used to evaluate hormone utilization.
Why it matters in Hashimoto’s: The ratio of Free T3 to Reverse T3 matters in practical terms because a patient can have Free T3 in the acceptable range but still have hypothyroid symptoms if Reverse T3 is high and occupying receptor sites.
Even a complete thyroid panel is only the beginning. Dr. Rubin's Functional Medicine approach investigates the conditions driving immune dysregulation in the first place.
Gut permeability. A compromised gut lining allows partially digested proteins into the bloodstream, triggering immune responses. Molecular mimicry between gliadin (a wheat protein) and thyroid tissue is one mechanism linking gut health to Hashimoto's flares. Our Functional GI approach can be crucial.
Nutritional deficiencies. Selenium is required for T4-to-T3 conversion and has been studied specifically for reducing TPO antibody levels. Iron, vitamin D, and zinc all play roles in immune regulation and thyroid hormone synthesis. Nutritional analysis and testing for low levels of essential vitamins and minerals may be key.
Chronic inflammation. Inflammatory cytokines actively inhibit T4-to-T3 conversion. We may also do tests to measure the levels of systemic inflammation in your body, including Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP). Addressing upstream inflammation — through diet, sleep, and stress management — is part of reducing antibody burden.
HPA axis dysregulation. Elevated cortisol from chronic stress impairs thyroid hormone receptor sensitivity and suppresses T4-to-T3 conversion, compounding the autoimmune picture.
It’s important to not just go beyond the standard TSH testing conventional medicine stops at, but to delve deeper than even the comprehensive thyroid panel we do. Taking a whole-person approach can reveal much more than conventional medicine and a standard TSH test ever will.
How can you tell if your condition calls for more than a standard TSH-only workup? Are you experiencing persistent fatigue despite "normal" labs? Are you continuing to gain weight or having difficulty losing weight? Are you losing hair, suffering with brain fog or becoming more intolerant to cold. Do you have a history of other autoimmune conditions or a family history of thyroid disease? If so, we’re here to help you understand what is happening inside your body.
Dr. Robert D. Rubin is a widely respected Functional Medicine practitioner in Florida with offices in Naples and Tampa, as well as a convenient telemedicine treatment program. He has extensive experience treating patients who are struggling with longevity and health concerns. Dr. Rubin specializes in Functional Medicine, bioidentical hormones, weight loss therapy, and sexual health treatments.
As an Advanced Fellow in the American Academy of Anti-Aging Medicine, who is also AMA Board Certified in Internal Medicine and Geriatrics Medicine, Dr. Rubin is a dedicated medical professional with an exceptional track record. He spent the first 25 years of his medical career working in internal and geriatric medicine, successfully becoming one of Palm Beach County’s top-rated physicians. For four years, Castle Connolly Medical, Ltd. recognized him as one of the “Top Doctors” in South Florida.
After further specialized training, he shifted his practice to a Functional Medicine approach to better serve the needs of his patients. Over the last 15 years, Dr. Rubin has honed his focus, creating a practice rooted in evidence-based healthcare that addresses the root causes of your symptoms.
Combining this with his expertise in Internal Medicine and Geriatrics, he provides a comprehensive approach to your health. Dr. Rubin always takes an individualized approach to treatment, recognizing that each patient has a different medical history, symptoms, and underlying issues. Listening attentively to your concerns, Dr. Rubin personalizes a treatment protocol to meet your needs, guiding you confidently on your lifelong health journey.
Dr. Rubin sees patients at both the Naples and South Tampa offices, and your Functional Medicine consultation includes a comprehensive thyroid panel as part of the initial evaluation. To revolutionize your approach to thyroid health, book online or call either of our offices today for in-person or telemedicine options.
