Beyond TSH: Lillea Hartwell on Why One Lab Test Isn't Enough for Thyroid Disorders

You've been exhausted for months. Your hair is thinning, your weight won't budge, and your brain feels like it's wrapped in cotton. Your doctor runs a blood test, tells you everything looks "fine," and sends you home. Sound familiar?

For millions of Americans living with undiagnosed or undertreated thyroid disorders, this scenario plays out on repeat. The problem isn't that their doctors don't care — it's that the standard screening approach relies on a single marker that can mask what's actually going wrong.

Lillea Hartwell, a naturopathic doctor practicing in Tucson, Arizona, has built her career around closing that gap. Her approach is straightforward: order more labs, ask better questions, and stop accepting "normal" as the final answer.

The Education Gap in Thyroid Medicine

That lack of education Hartwell describes isn't just anecdotal. Research continues to reveal how much conventional thyroid screening misses. A 2026 review in the Journal of the Association of Physicians of India highlighted the ongoing controversy around thyrotropin (TSH) interpretation in subclinical thyroid disorders, noting that reliance on TSH alone often fails to capture the full clinical picture.^[1] When a patient's TSH levels fall within the standard reference range but other markers tell a different story, the result is a diagnostic blind spot — and a patient left wondering why they still feel terrible.

The issue runs deeper than individual doctor visits. Thyroid education in medical training tends to follow a simplified algorithm: check TSH, prescribe levothyroxine if it's high, recheck in six weeks. This approach works for clear-cut cases. But thyroid dysfunction rarely presents in clear-cut ways — and that's where patients like Hartwell's fall through the cracks.

The Investigation: Root Cause Over Quick Fixes

Walk into Hartwell's Tucson practice and the first thing she wants isn't your symptom list — it's your history. Did someone else already diagnose you? What labs have actually been drawn? When? She treats the intake like an investigation, not a checklist.

The "cascade of hormones" she references includes markers many patients have never heard of. Beyond TSH, a thorough thyroid panel includes free T4 (the inactive hormone your thyroid produces), free T3 (the active form your cells actually use), and reverse T3 (a metabolically inactive form that can block T3 receptors). Then there are thyroid antibodies — TPO and thyroglobulin antibodies — which signal autoimmune activity.

This matters because autoimmune thyroid disease, particularly Hashimoto's thyroiditis, is the most common cause of hypothyroidism in the United States. A 2026 review in Frontiers in Endocrinology traced the full pathogenesis of Hashimoto's from immune triggers through progressive thyroid tissue destruction, emphasizing that early identification of autoimmune markers can change the treatment trajectory entirely.^[2] Yet many patients receive a hypothyroidism diagnosis — and a levothyroxine prescription — without ever being tested for the antibodies that reveal why their thyroid is failing.

The distinction between hypothyroidism and Hashimoto's isn't academic. It shapes treatment strategy. A patient whose thyroid is under attack from their own immune system may need a fundamentally different approach than someone with non-autoimmune hypothyroidism. Hartwell's observation about patients feeling differently "from their treatments" — even when medicated — often traces back to this overlooked autoimmune component. If antibodies are elevated and driving ongoing thyroid destruction, simply replacing thyroid hormone addresses the symptom without touching the cause.

A 2025 paper in Hormones examined the evolving understanding of Hashimoto's thyroiditis, noting that the condition encompasses a wider clinical spectrum than traditionally recognized — including patients with significant symptoms who haven't yet progressed to overt hypothyroidism.^[3] These are exactly the patients most likely to be told their labs look "fine." For a deeper look at what to watch for, our Hashimoto's symptoms checklist covers the warning signs that often go unrecognized.

The Three-Lab Minimum: Why TSH Alone Falls Short

If there's a single clinical hill Hartwell is willing to die on, it's this: one lab test is not enough.

TSH is a pituitary hormone — it tells you what the brain is asking the thyroid to do, not what the thyroid is actually producing or what the body can use. A patient can have a TSH of 2.5 (well within conventional range) while their free T3 is tanking or their antibodies are through the roof.

Understanding how to read a full thyroid panel is becoming critical for patients who want to advocate for their own care. The science backs up the need for broader testing: a 2024 study in Clinical Biochemistry used big data analysis across large populations to argue for redefining thyroid hormone reference intervals entirely, finding that current ranges may not accurately reflect healthy function across diverse demographics.^[4] In other words, "within normal limits" depends heavily on whose limits you're using — and for whom they were established.

Hartwell also raises a practical point about medication management. Many thyroid patients take levothyroxine (synthetic T4) but don't realize that timing, food interactions, and supplement interference can dramatically affect absorption. She asks her patients directly: are they following best practices while taking their medication? It's a simple question, but it often reveals compliance gaps that explain why someone on the right dose still feels wrong.

The downstream effects of undertreated thyroid dysfunction extend far beyond fatigue. A 2024 review in Cureus documented the significant impact of hypothyroidism on menstrual irregularities, linking suboptimal thyroid function to disrupted cycles, heavy bleeding, and fertility challenges.^[5] These systemic consequences underscore why settling for an incomplete lab picture carries real clinical risk. If you're exploring practitioners who specialize in this area, our thyroid support directory is a good place to start.

When "Fine" Isn't Good Enough

There's a quiet confidence in Hartwell's advice. She's not telling patients to fire their doctors. She's telling them to ask for more — more labs, more context, more investigation. In a medical system that often defaults to the quickest screening tool available, that request can feel radical. But for the millions of people whose thyroid dysfunction hides behind a "normal" TSH, it might be the most important thing they do.

The conversation around thyroid testing is shifting. Functional medicine practitioners, naturopathic doctors, and even some endocrinologists are pushing for comprehensive panels as a baseline — not an exception. Hartwell is part of that movement, and her patients are the evidence that looking deeper works.

If you've been told your thyroid is fine but your body keeps insisting otherwise, maybe it's not you. Maybe it's the test.