Comprehensive Blood Elements

Lead is a non-essential heavy metal with no physiological role. Whole-blood lead reflects both recent exposure and a component of release from bone stores during remodelling. It is a neurotoxin, nephrotoxin, and haematotoxin; even low-level chronic exposure impairs cognitive development in children and is associated with hypertension and renal impairment in adults. Lead binds to sulphydryl groups on proteins and interferes with enzymes in haem synthesis.

Blood lead is the standard biomarker for diagnosing recent or ongoing lead exposure and is used in occupational monitoring, environmental screening, and paediatric case-finding. Values above 5 µg/dL prompt investigation and intervention; higher levels warrant chelation and environmental remediation.

Mercury exists in elemental, inorganic, and organic (methylmercury) forms. Whole-blood mercury reflects predominantly organic mercury from dietary fish and seafood, while inorganic mercury from occupational or dental-amalgam sources contributes less. Methylmercury is neurotoxic, crosses the blood–brain and placental barriers, and accumulates in the central nervous system. Inorganic mercury is nephrotoxic.

Blood mercury is used to assess recent organic-mercury exposure in patients with high fish consumption, to investigate suspected acute mercury poisoning, and in occupational surveillance. Prenatal and childhood exposures are of greatest concern because of neurodevelopmental toxicity.

Cadmium is a toxic heavy metal with a biological half-life in the body measured in decades. Blood cadmium predominantly reflects recent exposure (smoking, occupational), while urinary cadmium reflects cumulative body burden and is the preferred marker for chronic exposure. Cadmium accumulates in the kidneys and causes proximal tubular damage; it is also a carcinogen and may contribute to osteoporosis.

Blood cadmium is useful in acute-exposure scenarios and occupational monitoring. For assessment of long-term body burden and renal toxicity, urinary cadmium is more informative. Tobacco smoke is the single largest non-occupational source.

Arsenic exists in inorganic (arsenite, arsenate) and organic (arsenobetaine, arsenocholine) forms. Inorganic arsenic is a known human carcinogen and causes peripheral neuropathy, skin lesions, and vascular disease. Organic arsenicals from seafood are non-toxic and rapidly excreted. Blood arsenic has a short half-life (hours to days) and is used for acute-exposure assessment; urinary speciated arsenic is preferred for chronic-exposure evaluation.

Blood arsenic is ordered when acute arsenic poisoning is suspected. Because seafood consumption can raise total arsenic without health risk, speciation is essential for interpretation. Chronic environmental or occupational exposure is better assessed by urinary arsenic.

Aluminium is the most abundant metal in the Earth's crust and enters the body through diet, occupational inhalation, and medical sources such as dialysis and parenteral nutrition. It is neurotoxic and was historically associated with dialysis dementia and osteomalacia in renal-failure patients exposed to high-aluminium dialysate. Gastrointestinal absorption is normally very low except in renal impairment or with citrate co-administration.

Blood aluminium is monitored in dialysis patients and those on long-term parenteral nutrition to prevent aluminium-related bone disease and encephalopathy. It is also ordered when occupational or environmental exposure is suspected. The test has limited utility in the general population.

Selenium is an essential trace element incorporated into selenoproteins, including glutathione peroxidases and thioredoxin reductases that protect against oxidative stress. It is also required for thyroid hormone metabolism via the iodothyronine deiodinases. Both deficiency (Keshan cardiomyopathy, Kashin-Beck osteoarthropathy) and toxicity (selenosis: hair loss, nail changes, neurological symptoms) are recognised.

Blood selenium reflects recent dietary intake and is used to assess selenium status in populations with marginal intake, in total parenteral nutrition, and when toxicity is suspected. Serum or plasma selenium correlates reasonably with tissue stores; red-cell selenium reflects longer-term status.

Zinc is an essential trace element serving as a cofactor for more than 300 enzymes and playing structural roles in zinc-finger transcription factors. It is critical for immune function, wound healing, protein synthesis, and DNA synthesis. Zinc homeostasis is tightly regulated, and serum zinc is influenced by acute-phase responses (falls during inflammation and infection), fasting state, and diurnal variation.

Serum zinc is ordered to investigate suspected deficiency (poor growth, impaired immunity, dermatitis, impaired taste) or, rarely, toxicity from excessive supplementation. Because inflammation lowers serum zinc independently of body stores, it should be interpreted with an acute-phase marker such as CRP.

Copper is an essential trace element required for cytochrome c oxidase, superoxide dismutase, and other cuproenzymes involved in energy production, antioxidant defence, and connective-tissue synthesis. Most serum copper is bound to caeruloplasmin, an acute-phase protein that rises in inflammation, pregnancy, and oestrogen therapy. Free (non-caeruloplasmin) copper is the metabolically active fraction and is elevated in Wilson disease.

Serum copper is ordered in the work-up of suspected copper deficiency (anaemia, neutropenia, myelopathy) or Wilson disease, where it is typically low or normal but free copper is elevated. Because caeruloplasmin is an acute-phase reactant, serum copper alone is insufficient for diagnosis; it is interpreted alongside caeruloplasmin and, in Wilson disease, urinary copper and slit-lamp examination.

Manganese is an essential trace element and cofactor for enzymes including superoxide dismutase, pyruvate carboxylase, and glycosyltransferases. It is tightly regulated, and excess manganese accumulates in the basal ganglia, producing a parkinsonian syndrome. Deficiency is rare outside of experimental settings.

Blood manganese is ordered in occupational medicine (welding, mining) to monitor for excessive exposure, in patients on long-term parenteral nutrition, and when environmental or dietary toxicity is suspected. Whole-blood measurement is preferred over serum.

Trivalent chromium (Cr³⁺) is considered an essential trace element involved in potentiating insulin action, though the evidence for essentiality is contested. Hexavalent chromium (Cr⁶⁺) is a toxic and carcinogenic industrial compound. Blood chromium reflects recent exposure; it is used primarily in occupational and implant surveillance rather than routine nutritional assessment.

Blood chromium is ordered when occupational exposure to chromium compounds is suspected or to monitor patients with metal-on-metal orthopaedic implants. It is not routinely used for nutritional assessment because chromium deficiency is exceedingly rare and the biological role of trivalent chromium remains debated.

Molybdenum is an essential trace element and cofactor for several enzymes, including sulphite oxidase, xanthine oxidoreductase, and aldehyde oxidase. Deficiency and toxicity are both rare; deficiency has been reported in patients on long-term total parenteral nutrition and presents with neurological symptoms and metabolic disturbances.

Blood molybdenum is ordered almost exclusively in the context of prolonged parenteral nutrition or suspected genetic defects in molybdenum-cofactor biosynthesis. It is not part of routine trace-element screening.

Cobalt is the central metal ion in vitamin B12 (cobalamin) and is thus indirectly essential, but free ionic cobalt has no known independent metabolic role in humans. Elevated blood cobalt from occupational exposure or metal-on-metal hip prostheses can cause cardiomyopathy, hypothyroidism, polycythaemia, and neurological damage.

Blood cobalt is ordered primarily to monitor patients with metal-on-metal orthopaedic implants and in occupational medicine. Sustained elevations are associated with systemic toxicity, and high cobalt levels after arthroplasty may prompt revision surgery.