Blood Spot Thyroids + Dried Urine ICPMS Toxic and Essential Elements

TSH is a glycoprotein hormone secreted by the anterior pituitary in response to hypothalamic thyrotropin-releasing hormone. It drives thyroid synthesis and release of T4 and T3 through a tight negative-feedback loop. Dried blood-spot measurement correlates well with serum assays, enabling remote collection while preserving the analyte.

TSH remains the first-line screening marker for thyroid dysfunction. Elevation signals primary hypothyroidism, while suppression suggests hyperthyroidism or overreplacement. In this panel TSH is paired with free T4 and T3 to distinguish central from primary disorders and to refine thyroid status before interpreting element exposures that may disrupt thyroid metabolism.

Free T4 represents the biologically active, unbound fraction of thyroxine. It circulates as the primary secretory product of the thyroid and is deiodinated peripherally to yield the more potent T3. Dried-spot immunoassay captures free T4 reliably when handled within stability windows.

Free T4 distinguishes primary from central thyroid disorders when TSH is abnormal and assesses adequacy of levothyroxine replacement. In toxicology screening, T4 can be suppressed by perchlorate, thiocyanate, or chronic heavy-metal exposure that impairs thyroid synthesis or transport.

Free T3 is the metabolically active thyroid hormone, generated predominantly by peripheral 5'-deiodination of T4 in liver, kidney, and other tissues. It binds nuclear receptors to regulate gene transcription across nearly every organ system.

Free T3 assesses peripheral conversion and the active hormonal pool. Low T3 despite normal T4 can reflect non-thyroidal illness, nutrient deficiencies (selenium, zinc), or toxicant-related deiodinase inhibition. High T3 in hyperthyroidism or T3-predominant Graves disease drives the clinical phenotype.

TPO antibodies target the enzyme that catalyses iodination of thyroglobulin. Their presence marks autoimmune thyroid disease, most commonly Hashimoto thyroiditis, and predicts progression from subclinical to overt hypothyroidism.

TPOAb confirms autoimmune aetiology when TSH or thyroid hormones are abnormal and identifies at-risk euthyroid patients. In a toxicology context, some practitioners hypothesise that environmental exposures may trigger or exacerbate autoimmunity, though causal links remain investigational.

Antibodies to thyroglobulin, the storage protein for thyroid hormones, occur in autoimmune thyroid disease and can interfere with serum thyroglobulin measurement used in thyroid-cancer surveillance.

TgAb positivity supports a diagnosis of Hashimoto or Graves disease and, when present alongside TPOAb, indicates more robust autoimmune activity. In this panel it completes the autoimmune screening component.

Urinary arsenic reflects recent exposure to inorganic and methylated arsenic species. Organic arsenicals from seafood (arsenobetaine, arsenocholine) are rapidly excreted and non-toxic, while inorganic arsenic and its methylated metabolites (monomethyl- and dimethylarsinic acid) carry carcinogenic and systemic toxicity.

Elevated urinary arsenic prompts evaluation of water supply, occupational or environmental sources, and dietary arsenical intake. Speciation (distinguishing inorganic from organic forms) is the gold standard when total arsenic exceeds reference limits, as seafood can produce misleadingly high totals without toxicity.

Cadmium accumulates in the renal cortex with a biological half-life of decades. Urinary cadmium reflects cumulative body burden rather than recent exposure and rises as renal metallothionein is saturated or tubular damage occurs.

Chronic cadmium exposure, chiefly from tobacco smoke, occupational inhalation, or contaminated food, causes proximal tubular dysfunction (Fanconi syndrome), osteomalacia, and increased cardiovascular risk. Monitoring is warranted in patients with known exposure or unexplained proteinuria.

Urinary mercury predominantly reflects inorganic mercury from dental amalgam vapour, occupational exposure, or inorganic salts. Organic (methyl-) mercury, the form bioaccumulated in fish, is better assessed in whole blood or hair.

Elevated urinary mercury suggests recent or ongoing elemental or inorganic mercury exposure. Neurological, renal, and immunological effects are dose-dependent. Chelation and source removal remain the mainstays of management when clinical toxicity is present.

Urinary lead correlates with recent soft-tissue exposure and mobilisable bone stores. Whole-blood lead is typically the preferred screening matrix, but urine can reflect chelatable burden or recent spike exposure.

Lead is a pervasive neurotoxin and nephrotoxin with no safe threshold. Sources include old paint, contaminated water, occupational exposure, and certain imported goods. Even low-level chronic exposure is associated with cognitive deficits, hypertension, and renal impairment.

More than ninety per cent of dietary iodine is excreted in urine, making spot urinary iodine a practical biomarker of recent intake. Iodine is the rate-limiting substrate for thyroid hormone synthesis, and both deficiency and excess can disrupt thyroid function.

Urinary iodine below 100 µg/L signals deficiency, a leading cause of hypothyroidism and goitre worldwide. Values above 300 µg/L may trigger autoimmune thyroiditis or iodine-induced hyperthyroidism in susceptible individuals. In this panel, iodine status contextualises thyroid hormone and antibody findings.

Selenium is a trace element integral to glutathione peroxidase and the iodothyronine deiodinases that convert T4 to T3. Urinary selenium reflects recent dietary intake and is more dynamic than whole-blood or serum levels.

Deficiency impairs antioxidant defence and peripheral thyroid hormone activation, manifesting as hypothyroid symptoms despite adequate iodine. Excess selenium from over-supplementation can cause selenosis (hair loss, nail changes, neuropathy) and paradoxically increase diabetes risk.

Zinc is a cofactor for hundreds of enzymes, including those involved in immune function, wound healing, and thyroid hormone metabolism. Urinary excretion increases with high dietary intake and in hypercatabolic states, but it is not the most sensitive marker of zinc status.

Low urinary zinc can reflect poor intake or redistribution during inflammation, but plasma or red-cell zinc is usually preferred for assessing deficiency. Elevated urinary loss occurs in some genetic disorders and during chelation therapy.

Copper is essential for cytochrome oxidase, superoxide dismutase, and connective-tissue cross-linking. Urinary copper rises dramatically in Wilson disease, where biliary excretion is blocked, and modestly in other hepatobiliary disorders.

Elevated urinary copper (especially >100 µg/24 h) is a hallmark of Wilson disease and requires correlation with caeruloplasmin and slit-lamp examination. Low levels can signal deficiency but are rarely the sole diagnostic criterion.

Magnesium is the second most abundant intracellular cation, critical for ATP-dependent processes, neuromuscular function, and bone health. Renal excretion adjusts rapidly to intake, making urinary magnesium a marker of recent dietary load and renal handling rather than total-body stores.

Low urinary magnesium can indicate poor intake or redistribution, but serum or red-cell magnesium is preferred for assessing deficiency. High urinary loss occurs with diuretics, alcohol, and certain tubular disorders.