Normal Is Not Optimal: The Lab Testing Gap and What Your Thyroid Panel Is Missing

Article 2 of 3

About eighteen months into her decline, Kathleen did something that many patients do when the medical system stops providing answers: she started doing her own research.

She wasn’t looking for fringe cures or internet conspiracy theories. She was looking for the thing her appointments had never given her — an explanation. Why, despite being on thyroid medication, despite her labs looking “acceptable,” despite doing everything her doctors asked, did she still feel like a diminished version of herself? Why did the fatigue persist? Why was her digestion still sluggish, her joints still aching, her mind still running at half speed?

She found Dr. Antonio Bianco’s book, Rethinking Hypothyroidism. She read about the deiodinase system. She read about the difference between TSH — the marker her doctors had been optimizing — and the tissue-level thyroid activity that TSH can’t see. She read about free T3, about reverse T3, about the ratio between them. And she realized, with a mixture of relief and fury, that in three years of thyroid treatment, nobody had ever measured the hormone that actually does the work.

Nobody had measured her free T3 with a precision assay. Nobody had checked her reverse T3. Nobody had looked at whether the medication she was taking was actually being converted into active hormone at the tissue level.

Her labs had been “normal.” Her thyroid, at the cellular level, had been anything but.

The Map With Half the Terrain Missing

In medicine, what you measure determines what you find. And what you don’t measure — what you assume is fine, what you consider irrelevant, what your lab panel simply doesn’t include — can determine what you miss for years.

The standard thyroid panel ordered by most primary care physicians in the United States — and by most endocrinologists — typically includes two values: TSH and free T4. Sometimes total T4 is added. Occasionally, free T3 is included. Reverse T3 is rarely ordered. A comprehensive autoimmune antibody panel is not standard. And the precision of the free T3 assay itself — the method by which the lab actually measures the number — is almost never specified by the ordering physician, despite the fact that the two available methods produce dramatically different results.

This is a map with half the terrain missing. And when you’re trying to navigate complex territory — the kind of territory Kathleen was lost in — a half-map is worse than useless. It gives you the confidence of having directions while pointing you the wrong way.

To understand what should be on a comprehensive thyroid panel, and why, we need to return to the biology we laid out in Article 1 — and follow it to its clinical conclusions.

TSH: The Most Useful Number That Isn’t Enough

Let’s start with what TSH does well, because it genuinely does something well.

TSH — thyroid stimulating hormone — is produced by the pituitary gland in response to signals from the hypothalamus. When thyroid hormone levels in the bloodstream fall, the pituitary responds by releasing more TSH, essentially sending an urgent message to the thyroid: produce more. When thyroid hormone levels are adequate, TSH falls quiet. It is a sensitive amplifier of the feedback loop — capable of detecting relatively small changes in circulating thyroid hormone and responding with large, measurable swings in TSH output.

This sensitivity is genuinely useful. A TSH above 10 with a low free T4 is the gold standard for diagnosing overt primary hypothyroidism. A suppressed TSH near zero in a patient on thyroid medication usually signals overtreatment. For initial screening, for monitoring gross adequacy of replacement therapy, and for identifying the two extremes of thyroid dysfunction, TSH is a reliable and well-validated tool.

But TSH has three fundamental limitations that make it insufficient as a standalone measure of thyroid health.

First, TSH measures the pituitary’s response — not the tissues’. The pituitary and hypothalamus are richly endowed with Type 2 deiodinase, the enzyme that converts T4 to T3 locally. This means the pituitary is exquisitely good at managing its own thyroid hormone environment. It can satisfy its own T3 needs even when peripheral tissues — the liver, the brain, the muscles, the gut — are running low. A patient on levothyroxine (T4 only) can have a perfectly normalized TSH while their liver remains relatively undertreated, their skeletal muscle remains sluggish, and their cognitive function remains impaired. The pituitary is satisfied. The rest of the body is not.

Second, TSH doesn’t reflect deiodinase activity in peripheral tissues. As we explored in Article 1, the deiodinase system — the network of enzymes that converts inactive T4 to active T3, or alternatively to the inactive reverse T3 — operates at the tissue level and cannot be directly measured in blood. Chronic illness, inflammation, stress, nutritional deficiencies, and autoimmune activity can all suppress peripheral deiodinase function, reducing the conversion of T4 to T3 in the tissues that need it most. TSH will not capture this. TSH reflects the pituitary’s comfortable relationship with circulating hormone levels. It says nothing about the conversion machinery in the periphery.

Third, TSH reference ranges were established in populations that included people with undiagnosed thyroid disease. The commonly used reference range of roughly 0.5 to 4.5 mIU/L was derived from large population studies — but those populations included people who were already in early-stage Hashimoto’s, people with subclinical hypothyroidism, and people with other undetected thyroid conditions. When you include a significant number of already-hypothyroid people in your “normal” population, your upper limit of normal shifts upward. Some researchers have argued that a truly healthy upper limit for TSH is closer to 2.5 mIU/L, not 4.5. This remains debated, but the point stands: “within the reference range” and “optimal” are not the same thing.

Free T4: Necessary But Not Sufficient

Free T4 — the unbound, biologically available fraction of the prohormone — is a useful and generally reliable measure of thyroid gland output. Unlike TSH, which reflects the pituitary’s response to thyroid hormone, free T4 directly reflects what the thyroid is producing and releasing. If free T4 is low, the thyroid is underperforming, full stop. This is why free T4 is essential in the diagnostic workup — a low free T4 paired with an elevated TSH confirms overt hypothyroidism; a low free T4 with a normal TSH raises the possibility of central (pituitary or hypothalamic) hypothyroidism.

Free T4 also has a methodological advantage: the immunoassay used by standard labs to measure it is reasonably accurate and well-validated. You can generally trust the number you get from a reputable laboratory.

But free T4 alone tells you nothing about what happens after the prohormone leaves the bloodstream. It tells you nothing about conversion. It tells you nothing about whether T4 is being efficiently transformed into T3 in the tissues. It tells you nothing about whether the active hormone is actually reaching the cell nucleus and doing its job.

Think of free T4 as measuring the supply of raw ingredients in the kitchen. It tells you whether the pantry is stocked. It does not tell you whether a meal is being cooked, whether the stove is working, or whether anyone at the table is being fed.

For patients on levothyroxine — which is pure T4 — free T4 is particularly limited as a measure of treatment adequacy. The entire therapeutic bet of levothyroxine is that the deiodinase system will convert that T4 into T3 efficiently and distribute it appropriately to the tissues. For most patients, most of the time, that bet pays off. But for the 10-20% of patients who continue to feel unwell despite normalized TSH and free T4 — patients exactly like Kathleen — the bet has not paid off, and free T4 cannot tell you why.

Free T3: The Number That Actually Matters Most — And the Problem With How We Measure It

T3 is the biologically active thyroid hormone. It is the molecule that binds to receptors, enters cell nuclei, regulates gene expression, and drives every physiological process we associate with adequate thyroid function — metabolic rate, heart rate, body temperature, cognitive clarity, gut motility, mood, energy. Every clinical effect of thyroid hormone, positive or negative, is ultimately mediated by T3.

Given this, it seems almost incomprehensible that free T3 is not universally included in thyroid panels. The conventional justification — still taught and still practiced — is that free T3 is “not necessary” for diagnosis or monitoring, that TSH and free T4 are sufficient. This position, as Antonio Bianco has argued forcefully in his research and his book, reflects an incomplete understanding of thyroid physiology that has persisted in clinical medicine long after the basic science moved past it.

Free T3 should be measured in any patient who:

Has symptoms of hypothyroidism despite normalized TSH and free T4
Is being evaluated for adequacy of thyroid hormone replacement
Has a known or suspected deiodinase conversion problem
Is being considered for combination T4/T3 therapy
Has chronic illness, significant inflammatory burden, or severe psychological stress that may be suppressing peripheral conversion

But here is the catch — and it is a significant one that most patients and many physicians don’t know: not all free T3 measurements are equal. The standard immunoassay used by most laboratories to measure free T3 is, by the assessment of thyroid specialists, unreliable. Particularly at lower levels of T3 — exactly the range that matters most in hypothyroidism — the immunoassay diverges significantly from the gold standard measurement method.

That gold standard is liquid chromatography-tandem mass spectrometry, or LC-MS/MS. Mass spec measures T3 directly and precisely, without relying on the antibody-based detection system that makes immunoassays prone to interference and inaccuracy. Studies comparing the two methods have shown that at the lower end of the T3 range, the immunoassay produces numbers that can be meaningfully wrong — either falsely normal or falsely abnormal — while mass spec provides an accurate value.

This is not an abstract methodological concern. It is the difference between a number you can make clinical decisions from and a number that may be misleading you.

For context: in the world of sex hormone testing, this problem is well-recognized. Any clinician managing testosterone therapy would specify LC-MS/MS for testosterone measurement — an immunoassay testosterone is considered clinically unreliable and most serious practitioners discard it entirely. The free T3 problem is directly analogous, and yet the medical community has been far slower to adapt. Most standard labs — including major national laboratories — still default to immunoassay for free T3 unless LC-MS/MS is specifically requested.

For patients in Southern Oregon seeking a precision free T3 measurement: you will need to specifically request LC-MS/MS methodology when ordering free T3. This test is available through major reference laboratories, though it may require your physician to order it explicitly and may involve additional cost. It is worth both the conversation and the cost.

Reverse T3: The Inactive Decoy and What It Tells Us

If free T3 is the active key that opens thyroid receptors, reverse T3 is a structural imposter — a molecule with almost identical shape but no biological function. It is produced when T4 is converted not by the activating enzyme (D2) but by the inactivating enzyme (D3), or in smaller amounts by D1. Reverse T3 cannot activate thyroid receptors. It is, in terms of thyroid biology, dead weight.

But it is not clinically irrelevant.

Reverse T3 rises when the body is under conditions of physiological stress — fasting, serious illness, inflammation, caloric restriction, psychological trauma, and the sustained inflammatory burden of autoimmune disease. This is the body deliberately downregulating thyroid activity: D3 ramps up, D1 falls, T4 is preferentially shunted away from T3 production and toward reverse T3 production. At the same time, D1 — which normally clears reverse T3 from circulation — is suppressed, so reverse T3 builds up in the blood.

The clinical consequence is a patient whose bloodstream looks relatively normal — TSH adequate, free T4 in range, even free T3 within the reference interval — but who has an elevated reverse T3 occupying what should be receptor space, and a T3-to-reverse-T3 ratio that tells a story of metabolic suppression.

The ratio of free T3 to reverse T3 is the best available blood-based surrogate for deiodinase activity — for understanding whether the body’s conversion machinery is working in favor of activation or suppression. It is imperfect; both T3 and reverse T3 are subject to production and clearance dynamics that complicate interpretation. But it is the closest thing we have, in routine clinical practice, to a window into what is happening at the tissue level.

A useful target ratio of free T3 to reverse T3 is generally considered to be above 0.2 when both are measured in the same units (or above 20 when free T3 is in pg/mL and reverse T3 is in ng/dL — confirm units with your laboratory). A ratio significantly below this suggests that the deiodinase balance is skewed toward inactivation — that the body is, for whatever reason, throttling thyroid activity even in the presence of adequate circulating hormone.

The reverse T3 assay itself has methodological limitations. Like free T3, it is better measured by mass spectrometry than immunoassay, and immunoassay values can vary significantly between laboratories. This means that consistency matters: if you are tracking reverse T3 over time, use the same laboratory. Don’t try to compare a value from one lab’s immunoassay with another lab’s result and draw conclusions from the difference.

The Antibody Panel: Why It Matters Beyond Diagnosis

Most physicians who check thyroid antibodies do so once — at initial diagnosis — and never revisit them. A positive TPO antibody confirms Hashimoto’s as the likely cause of hypothyroidism, satisfies the diagnostic algorithm, and the conversation moves on to dosing levothyroxine.

This is a missed opportunity.

As we discussed in Article 1, Hashimoto’s is not a disease that stays confined to the thyroid. The same immune dysregulation that generates anti-TPO antibodies can generate antibodies against other tissues. Approximately 30% of Hashimoto’s patients carry antibodies against brain tissue. Elevated anti-TPO is associated with significantly higher rates of miscarriage, preterm birth, depression, and cognitive dysfunction — independent of whether overt hypothyroidism is present.

There is growing evidence — not yet standard of care, but scientifically credible — that the magnitude of anti-TPO elevation correlates with the aggressiveness of the autoimmune process, and that interventions that reduce TPO antibody titers (selenium supplementation, vitamin D optimization, and in some cases low-dose naltrexone or dietary modifications) can slow the destruction of thyroid tissue and reduce systemic autoimmune burden.

This means anti-TPO antibody levels are not just a diagnostic checkbox. They are a dynamic biomarker that, when tracked over time, can tell you whether the autoimmune process is accelerating, stable, or responding to intervention. Monitoring them periodically — perhaps annually in a patient with known Hashimoto’s — provides clinically relevant information that a TSH never will.

Anti-thyroglobulin antibodies (anti-Tg) are a second antibody worth measuring, particularly in patients with Hashimoto’s whose anti-TPO is negative or equivocal. Anti-Tg targets thyroglobulin, the protein scaffolding on which thyroid hormones are assembled. Anti-Tg positivity can confirm autoimmune thyroiditis even when anti-TPO is absent, and it is also used in monitoring for thyroid cancer recurrence in patients who have undergone thyroidectomy.

What Kathleen’s Labs Should Have Looked Like

Let’s reconstruct, concretely, what a comprehensive thyroid evaluation for Kathleen should have included — and what her standard panel missed.

What Kathleen received:

TSH ✓
Free T4 ✓
Anti-TPO (once, at initial diagnosis) ✓

What was missing:

Free T3 by LC-MS/MS ✗
Reverse T3 ✗
Free T3 to reverse T3 ratio ✗
Anti-TPO tracked over time ✗
Anti-thyroglobulin antibodies ✗
Assessment of nutritional cofactors that affect thyroid conversion (selenium, zinc, ferritin, vitamin D) ✗

None of the missing elements are exotic or experimental. They are all measurable with existing laboratory technology. Several of them — free T3, reverse T3, anti-Tg — are available at major national reference laboratories. The nutritional markers are available at any standard lab. The question is not whether these tests exist. The question is why they aren’t ordered.

The answer is partly educational — many PCPs and endocrinologists were trained in a framework that considers TSH and free T4 sufficient, and haven’t been exposed to the research that challenges this. Partly it is systemic — standard electronic health record order sets default to the minimal panel, and deviating from defaults requires deliberate action. Partly it is economic — insurance coverage for extended thyroid panels is inconsistent, and physicians are understandably reluctant to order tests that may not be covered and may require lengthy prior authorization battles.

But partly — and this is the part that needs to change — it is a failure of clinical imagination. A failure to ask, when a patient sits across from you and describes three years of worsening fatigue, brain fog, chronic pain, and constipation despite “normal” thyroid labs, whether normal and adequate might be two different things.

The Nutritional Dimension: What the Deiodinases Need to Work

A comprehensive thyroid evaluation cannot stop at thyroid hormones and antibodies. The deiodinase enzymes — the conversion machinery that determines whether T4 becomes active T3 or inactive reverse T3 — depend on specific nutritional cofactors to function. Deficiencies in these cofactors can impair conversion even when the thyroid is producing adequate T4 and the medication is being taken correctly.

Selenium is the most critical. The deiodinase enzymes are selenoproteins — they require selenium as an essential structural component. Without adequate selenium, D1 and D2 activity decreases, T4-to-T3 conversion slows, and reverse T3 can accumulate. Selenium deficiency is not rare, particularly in regions with selenium-depleted soils — and parts of the Pacific Northwest, including Southern Oregon, sit in areas where selenium soil content can be low. Selenium also has direct anti-inflammatory effects on the thyroid gland, and multiple clinical trials have shown that selenium supplementation reduces anti-TPO antibody titers in Hashimoto’s patients. Measuring serum selenium or selenoprotein P is a reasonable part of a comprehensive thyroid workup.

Iron and ferritin deserve attention because thyroid peroxidase — the enzyme that catalyzes the incorporation of iodine into thyroid hormone — is an iron-dependent enzyme. Iron deficiency doesn’t just cause anemia; it directly impairs thyroid hormone synthesis. Moreover, many of the symptoms of iron deficiency overlap substantially with hypothyroidism: fatigue, brain fog, cold intolerance, hair loss. A patient who appears to have inadequately treated hypothyroidism may in fact be iron-deficient, or may be dealing with both problems simultaneously. Ferritin — a measure of iron stores — should be evaluated in any patient with persistent hypothyroid-type symptoms. A ferritin below 50-70 ng/mL can impair thyroid function even in the absence of frank anemia.

Vitamin D is both a cofactor in immune regulation and directly relevant to the autoimmune dimension of Hashimoto’s. Vitamin D receptor signaling has significant immunomodulatory effects — low vitamin D is associated with increased autoimmune activity broadly, and with higher anti-TPO antibody titers specifically. Southern Oregon, despite its relatively sunny summers, produces a population that is significantly vitamin D deficient through the long gray winters, particularly among people who work indoors. Measuring 25-hydroxyvitamin D and optimizing levels to 50-80 ng/mL is low-cost, low-risk, and supported by evidence in the context of autoimmune thyroid disease.

Zinc is a less-discussed but genuinely relevant cofactor. Zinc deficiency impairs the conversion of T4 to T3, and zinc supplementation has been shown in small trials to improve thyroid hormone metabolism. Zinc deficiency is not uncommon, particularly in populations with poor dietary diversity, gastrointestinal malabsorption, or high physiological stress — all conditions that overlap significantly with the hypothyroid population.

These nutritional assessments are not the province of functional medicine alone. They are basic biochemistry. Any physician caring for a patient with persistent hypothyroid symptoms despite adequate hormone replacement should be asking whether the enzymatic machinery that processes that hormone has everything it needs to function.

The Precision Problem: Why Methodology Matters

One of the most underappreciated issues in thyroid testing is that the same test, ordered from different laboratories or performed with different methods, can produce different numbers — numbers that may not be directly comparable and may lead to different clinical decisions.

This is particularly acute for free T3 and reverse T3, as discussed above. But it also applies, in subtler ways, to free T4 and even TSH. Reference ranges vary between laboratories. Immunoassay calibration differs between manufacturers. A free T4 of 0.9 ng/dL on one lab’s platform may represent a different biological reality than a 0.9 ng/dL on another’s.

The practical implications for patients and clinicians:

For free T3, always specify LC-MS/MS methodology. The immunoassay is not clinically reliable, particularly at lower T3 levels. If your laboratory doesn’t offer mass spec for free T3, consider using a reference laboratory that does.

For reverse T3, use the same laboratory over time. The absolute value is less important than the trend and the ratio to free T3. Cross-laboratory comparisons are unreliable.

For TSH and free T4, consistency matters. If you are tracking thyroid function longitudinally, use the same laboratory platform whenever possible. Switching laboratories mid-course can produce apparent changes in values that reflect methodological differences rather than biological changes.

For anti-TPO, the same principle applies: use the same laboratory for serial measurements to ensure comparability over time.

This is the kind of guidance that falls through the cracks of standard care — not because anyone is being negligent, but because nobody in the system is specifically tasked with thinking about it. The physician orders the test. The laboratory runs whatever method it defaults to. The result comes back as a number. The number gets compared to a reference range. The conversation moves on.

The patient, meanwhile, is making decisions based on numbers that may not mean what they appear to mean.

A Practical Roadmap: What to Ask For

For patients in Southern Oregon who want to advocate for a more comprehensive thyroid evaluation, here is a concrete framework to bring to your next appointment. This is not a demand list — it is a starting point for a conversation with your physician about whether your current evaluation is capturing everything it should.

For initial evaluation or when symptoms persist despite treatment:

TSH (standard immunoassay is acceptable)
Free T4 (standard immunoassay is acceptable)
Free T3 — request LC-MS/MS methodology specifically
Reverse T3
Anti-TPO antibodies
Anti-thyroglobulin antibodies
Ferritin
25-hydroxyvitamin D
Serum selenium (or include in a comprehensive micronutrient panel)
Zinc

For ongoing monitoring in a patient on thyroid replacement:

TSH
Free T4
Free T3 by LC-MS/MS
Reverse T3 (particularly if symptoms persist or worsen)
Anti-TPO annually (to track autoimmune activity over time)
Free T3 to reverse T3 ratio (calculated from the above; target above 0.2 when values are in comparable units)

Questions to ask your physician:

“My free T3 has never been measured with a precision assay — can we order it by LC-MS/MS?”
“Has my reverse T3 ever been checked? If my free T3 to reverse T3 ratio is low, what would that tell us?”
“Have you checked my ferritin, selenium, and vitamin D? Could any of these be affecting my thyroid hormone conversion?”
“My anti-TPO antibodies were checked once at diagnosis — should we be tracking them over time to see how the autoimmune process is progressing?”
“Is it possible my TSH looks normal because my pituitary is satisfied, even though my peripheral tissues aren’t getting enough T3?”

For Primary Care Physicians: The Monday Morning Protocol

For PCPs in Southern Oregon who want to practice at the leading edge of thyroid care within the bounds of current evidence, here is a practical framework:

At initial hypothyroidism diagnosis: Order TSH, free T4, free T3 (LC-MS/MS), reverse T3, anti-TPO, anti-Tg, ferritin, 25-hydroxyvitamin D, and selenium. This baseline panel takes one blood draw and provides a comprehensive picture of both hormonal status and the factors that influence conversion and autoimmune activity.

At follow-up visits: Routinely include free T3 by LC-MS/MS alongside TSH and free T4. For patients on levothyroxine, a normal TSH with low-normal free T3 and elevated reverse T3 is a signal worth investigating — it suggests peripheral conversion is not keeping up and combination therapy may warrant consideration.

When patients report persistent symptoms despite normal TSH and free T4: Before attributing symptoms to depression, menopause, stress, or aging, check free T3 by LC-MS/MS, reverse T3, ferritin, vitamin D, and selenium. These investigations cost little, carry no risk, and can reveal addressable causes of continued suffering.

Treat hypothyroidism as a cardiometabolic risk factor: Recent research, including a large retrospective study comparing over one million hypothyroid patients on levothyroxine with a matched healthy population, found a 2.5-fold increase in mortality — predominantly from cardiometabolic causes — in the treated hypothyroid group. Patients with hypothyroidism have structurally impaired LDL clearance that may not fully normalize even when TSH is controlled, which is why statins are the most commonly co-prescribed medication with levothyroxine. Monitor lipids closely, assess cardiovascular risk proactively, and don’t assume that a normalized TSH means the cardiometabolic picture has been corrected.

Consider the integration opportunity: Southern Oregon has a robust community of functional medicine practitioners who are, in many cases, already ordering more comprehensive thyroid panels, addressing nutritional cofactors, and recommending evidence-based lifestyle interventions. Rather than dismissing this work, consider whether communication channels can be established — shared records, coordinated care plans, a common vocabulary around these biomarkers — that would allow functional and conventional approaches to reinforce each other rather than operate in parallel silos.

Back to Kathleen

Armed with the research she had done, Kathleen returned to her primary care physician — not with hostility, but with a list. A careful, evidence-based, respectful list of tests she wanted ordered and the reasons she wanted them.

Her physician, to her credit, listened. She pushed back on a few items, explained her reasoning for some of the limitations, and agreed to order what she could. She was honest about which tests might not be covered by insurance and said she would try. She ordered free T3 by LC-MS/MS. She ordered reverse T3. She checked ferritin and vitamin D and selenium.

The results, when they came back, told a story that three years of TSH and free T4 measurements had entirely missed.

Kathleen’s free T3 by mass spec was low — not clinically low by the reference range, but meaningfully low relative to what optimal tissue-level thyroid function requires. Her reverse T3 was elevated. Her ratio was well below 0.2 — evidence of significant deiodinase suppression. Her ferritin was 18 — depleted iron stores that had been impairing both thyroid synthesis and her body’s ability to manufacture hemoglobin. Her vitamin D was 22 ng/mL — significantly deficient, contributing to the persistence of autoimmune activity. Her selenium was in the lower quarter of the reference range.

None of these findings were dramatic. None of them would have triggered an alert in a standard lab panel. But together, they painted a coherent picture of a patient whose thyroid hormone conversion machinery was running on depleted fuel, whose autoimmune process was not being addressed, and whose standard treatment — optimized for her pituitary’s satisfaction rather than her peripheral tissue’s needs — was leaving her systematically undertreated.

For the first time in three years, Kathleen had a map that matched the terrain.

What happened next — how her treatment changed, what combination of interventions finally moved the needle, and what a truly integrated approach to hypothyroidism looks like when conventional medicine and functional medicine work together — is the subject of Article 3.

Key Takeaways — Article 2

The standard thyroid panel of TSH and free T4 is insufficient for patients with persistent symptoms despite “normal” labs. It measures pituitary satisfaction and thyroid output — not peripheral conversion or tissue-level hormone availability.
Free T3 must be measured by LC-MS/MS, not immunoassay. The immunoassay is methodologically unreliable, particularly at lower T3 levels. Patients should specifically request this methodology.
Reverse T3 provides the best available blood-based window into deiodinase activity. Elevated reverse T3 with low or low-normal free T3 suggests significant metabolic suppression that TSH will not capture.
The free T3 to reverse T3 ratio is a clinically useful surrogate for deiodinase balance. A ratio below 0.2 (with values in comparable units) warrants investigation.
Anti-TPO antibodies should be tracked over time in Hashimoto’s patients — not checked once and forgotten. They are a dynamic biomarker of autoimmune activity.
Selenium, ferritin, vitamin D, and zinc are essential cofactors for thyroid hormone conversion and autoimmune regulation. They should be evaluated in any patient with persistent hypothyroid symptoms.
Hypothyroidism is a cardiometabolic risk factor. Mortality in treated hypothyroid patients remains 2.5 times higher than in healthy controls, driven primarily by cardiometabolic disease. LDL clearance may remain impaired even when TSH normalizes.
Southern Oregon PCPs have an opportunity to lead by building integrated care pathways that bring conventional and functional medicine approaches together around a shared, evidence-based diagnostic framework.

Next: Article 3 — “Rethinking the Playbook: What Good Thyroid Treatment Actually Looks Like — and What Southern Oregon Needs to Build”

Editorial Disclaimer

This article is investigative health journalism produced by Reimagine Healthcare, a Southern Oregon initiative dedicated to closing the gap between emerging medical evidence and everyday clinical practice. It is not medical advice, does not constitute a clinical recommendation, and is not a substitute for the individualized care of a licensed healthcare provider. The information presented here is drawn from peer-reviewed research, published scientific literature, and the work of recognized experts in thyroid physiology. Readers are encouraged to use this material to inform conversations with their own physicians — not to replace them. If you have concerns about your thyroid health, please consult a qualified medical professional. Reimagine Healthcare does not endorse any specific laboratory, pharmacy, supplement, or treatment protocol.