Mercury, blood measures recent exposure to a neurotoxic heavy metal that readily crosses the blood–brain and placental barriers. Most circulating mercury is methylmercury from fish and marine mammals; smaller fractions can reflect elemental or inorganic sources. Because mercury targets neurons, kidneys, and the cardiovascular and immune systems, this test matters for brain health, child development, pregnancy, and long‑term organ function.Typical laboratory ranges sit at very low values; optimal tends to be toward the low end. Blood levels mirror exposure over the prior several weeks, making this a useful snapshot of current body burden, especially for methylmercury.When values are low or near zero, they simply reflect minimal exposure. Mercury has no beneficial physiologic role, so low results do not cause symptoms. In women who are pregnant or may become pregnant, and in children and teens with developing brains, lower levels are particularly desirable because vulnerability to neurotoxicity is higher.Higher values indicate recent significant exposure. The nervous system is most sensitive: people may notice tingling in hands or feet, trouble with coordination, visual field constriction, tremor, headaches, irritability, or sleep changes. Children can show learning or behavioral effects, and fetal exposure can impair neurodevelopment. The kidneys may develop tubular injury with protein in the urine, and immune dysregulation and rashes can occur with inorganic forms. Elevated levels have also been linked to higher blood pressure and increased cardiovascular risk.Big picture: blood mercury connects environmental exposure to neurologic integrity, renal function, and heart health. Interpreted alongside exposure history and, when needed, urine mercury (for inorganic/elemental forms), it helps gauge risk for cognitive effects, kidney dysfunction, and adverse pregnancy and developmental outcomes.
