🌡️ On Thyroid Hormone or a Thyromimetic

What this panel can settle, and by what logic

Nine markers for the reader whose TSH (Thyroid-Stimulating Hormone) is suppressed on purpose, and who needs to know whether the dose is doing what they think.

1. SHBG (Sex Hormone-Binding Globulin) is the closest available readout of thyroid hormone action in tissue, and it is the reason to buy this panel rather than a cheaper one. The liver increases SHBG production in response to thyroid hormone, which makes it a downstream marker of effect rather than of concentration. Its value as such is clearest in resistance to thyroid hormone beta, where circulating hormone is high and the liver response separates tissues that are responding from tissues that are not Moran 2021.
2. TSH (Thyroid-Stimulating Hormone) with Free T4 (Thyroxine) and Free T3 (Triiodothyronine) is the minimum set once you are taking hormone. TSH alone is uninterpretable on any exogenous thyroid protocol, and the assays themselves carry known pitfalls Van Uytfanghe 2023Razvi 2019. The pattern of a raised thyroid hormone with a nonsuppressed TSH has its own diagnostic approach, which is worth knowing exists before assuming a lab error Moran 2023.
3. Reverse T3 separates a low free T3 caused by the dose from a low free T3 caused by everything else. Illness, hard training and low energy availability all shunt T4 toward reverse T3, and the distinction changes whether the answer is more hormone or more food.
4. Ferritin is on the panel because iron deficiency blunts peripheral conversion, and it is a common reason a stable dose stops working without anything about the dose having changed.
5. The Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) is a slow honest average. Cholesterol falls as thyroid exposure rises, over weeks, which makes it harder to game with a well-timed draw than any single hormone value.
6. The Complete Blood Count (CBC) with Differential and Comprehensive Metabolic Panel (CMP) are the baseline any continuously run compound needs.

What it cannot settle, and what would

It cannot tell you what your heart is doing, and that is the consequence that matters most. Atrial fibrillation is the endpoint of sustained thyroid excess, and it is found on an ECG or a wearable rather than in a tube. A resting heart rate taken every morning is a better early warning than a quarterly panel, which is the same argument compound_interference makes about this class generally.

It cannot measure bone. Sustained TSH suppression is associated with lower lumbar bone mineral density, measured directly with imaging rather than inferred Einspieler 2023. If you have run a suppressive dose for years, a DEXA scan is the measurement worth buying and no blood marker replaces it.

It cannot verify what is in an unregulated product. Thyroid hormone misuse is enough of a problem in sport to have generated its own regulatory literature Gild 2022, and a free T3 that does not move on a dose that should have moved it says the product, the absorption or the dose is not what you think.

And it cannot separate a suppressed TSH caused by your dose from one caused by an underlying thyroid problem without a period off hormone, which is a clinical decision rather than a lab one Van Uytfanghe 2023.

Draw conditions that decide whether the money is wasted

Draw timing relative to the dose decides most of these numbers.

1. Draw before the dose, not after. On any T3-containing protocol a post-dose sample catches a peak that has nothing to do with average exposure; on T4 the half-life of about a week makes timing much less critical. Write the exact hours since the last dose on the requisition Van Uytfanghe 2023.
2. Not within 6 weeks of a dose change. T4 takes that long to reach a new steady state, so an earlier draw reports a system still moving.
3. No biotin for 72 hours. It distorts thyroid immunoassays in both directions depending on the platform, and it is in most hair, skin and nail products Li 2020.
4. Morning, fasted 9 to 12 hours for the Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) and Comprehensive Metabolic Panel (CMP).
5. Do not draw within 2 weeks of an illness, because the non-thyroidal illness pattern will make the Free T3 (Triiodothyronine) and Reverse T3 read like a dosing problem.

How you would know it answered your question, and what each pattern means next

Four patterns, and what confirms each on the retest.

• Suppressed TSH (Thyroid-Stimulating Hormone), normal Free T4 (Thyroxine), normal Free T3 (Triiodothyronine), normal SHBG (Sex Hormone-Binding Globulin): replaced and stable. The suppressed TSH is the expected consequence of taking hormone, not the finding Van Uytfanghe 2023.
• Suppressed TSH (Thyroid-Stimulating Hormone) with a raised Free T3 (Triiodothyronine) and a rising SHBG (Sex Hormone-Binding Globulin) across two draws: genuine over-exposure at tissue level. SHBG falling back is what confirms a dose reduction has actually landed Moran 2021.
• Low Free T3 (Triiodothyronine) with a raised Reverse T3 on an unchanged dose: look at energy intake, illness and training load before changing anything, because more hormone does not fix a conversion shift driven by any of those.
• Raised Free T4 (Thyroxine) or Free T3 (Triiodothyronine) with a NONSUPPRESSED TSH (Thyroid-Stimulating Hormone): that combination has its own differential including assay interference and is worth investigating rather than dosing around Moran 2023.

Sources read for these sections

• Gild ML, et al. Thyroid Hormone Abuse in Elite Sports: The Regulatory Challenge. Journal of Clinical Endocrinology and Metabolism 2022 · PMID 35438767
• Einspieler H, et al. Effects of short- and long-term TSH suppression on lumbar bone mineral density in both genders using PET/CT. Scientific Reports 2023 · PMID 38114753
• Moran C, et al. Dyslipidemia, Insulin Resistance, Ectopic Lipid Accumulation, and Vascular Function in Resistance to Thyroid Hormone beta. Journal of Clinical Endocrinology and Metabolism 2021 · PMID 33524107
• Van Uytfanghe K, et al. Thyroid Stimulating Hormone and Thyroid Hormones (Triiodothyronine and Thyroxine): An American Thyroid Association-Commissioned Review of Current Clinical and Laboratory Status. Thyroid 2023 · PMID 37655789
• Moran C, et al. Approach to the Patient With Raised Thyroid Hormones and Nonsuppressed TSH. Journal of Clinical Endocrinology and Metabolism 2023 · PMID 37988295
• Razvi S, et al. Challenges in Interpreting Thyroid Stimulating Hormone Results in the Diagnosis of Thyroid Dysfunction. Journal of Thyroid Research 2019 · PMID 31662841
• Li D, Ferguson A, Cervinski MA, Lynch KL, Kyle PB. AACC Guidance Document on Biotin Interference in Laboratory Tests. J Appl Lab Med 2020 · PMID 32445355