What clinical biomarkers can practitioners reference on BiomarkersLabs.com?

Autoantibodies targeting thyroglobulin, the precursor protein for thyroid hormones. Secondary autoimmune thyroid marker.

Tests

1 test

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Reference range

<40 IU/mL (negative)

Ascorbic acid is a water-soluble antioxidant vitamin that humans cannot synthesise endogenously due to the absence of the enzyme L-gulonolactone oxidase. It is absorbed in the small intestine via sodium-dependent vitamin C transporters (SVCT1/SVCT2) and circulates primarily in plasma, with tissue concentrations substantially higher than plasma — particularly in the adrenal glands, leucocytes, and brain. Plasma half-life is approximately 10–20 days at physiological concentrations. The vitamin participates in collagen hydroxylation, catecholamine synthesis, iron absorption enhancement, and broad antioxidant defence.

Tests

1 test

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Reference range

0.4–2.0 mg/dL (23–114 µmol/L)

Free T4 represents the unbound, biologically active fraction of circulating thyroxine — typically 0.02–0.04% of total T4. The remaining 99.96%+ is bound to thyroid binding globulin (TBG), transthyretin, and albumin. Only the free fraction is available to enter target tissues, undergo deiodination to T3, and exert thyroid hormone activity. Half-life of approximately 6–7 days, with steady-state status reflecting roughly 4–6 weeks of thyroid function.

Tests

1 test

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Reference range

0.8–1.8 ng/dL (10–23 pmol/L)

The active thyroid hormone at cellular level. Produced primarily by peripheral conversion of T4 to T3 via deiodinase enzymes.

Tests

1 test

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Reference range

2.3–4.2 pg/mL (3.5–6.5 pmol/L)

Inactive T4 metabolite produced when the body shunts T4 away from active T3 production. Elevated in chronic illness, stress, and impaired conversion states.

Tests

1 test

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Reference range

9.2–24.1 ng/dL

Autoantibodies targeting thyroid peroxidase, the enzyme responsible for thyroid hormone synthesis. Primary serological marker for autoimmune thyroid disease.

Tests

1 test

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Reference range

<35 IU/mL (negative)