Mercury Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Mercury?

Mercury is a naturally occurring heavy metal that exists in three primary forms: elemental (metallic) mercury, inorganic mercury compounds, and organic mercury — most commonly methylmercury. Like lead, mercury serves no beneficial biological function in the human body and is toxic at elevated concentrations. It is one of the World Health Organization's top ten chemicals of major public health concern.

Methylmercury is the form of greatest concern for the general population because it bioaccumulates in the aquatic food chain. Large predatory fish — such as swordfish, shark, king mackerel, and tuna — concentrate methylmercury in their tissues to levels many thousands of times higher than surrounding waters. When consumed, methylmercury is readily absorbed from the gastrointestinal tract (approximately 95% absorption) and distributed throughout the body, with particular affinity for the nervous system.

Elemental mercury exposure occurs primarily through occupational settings (dental amalgams, thermometer breakage, certain industrial processes) and inhalation of mercury vapour. Inorganic mercury compounds are found in some traditional remedies, skin-lightening creams, and industrial chemicals.

A blood mercury test measures the total concentration of mercury in your blood. This primarily reflects recent exposure to organic (methylmercury) compounds, as methylmercury has a blood half-life of approximately 50–70 days. For assessing long-term or chronic exposure, hair and urine mercury tests may also be used.

Why Is Mercury Tested?

Mercury testing is performed in a range of clinical and occupational scenarios:

• High fish consumption: Individuals who eat large quantities of predatory fish (swordfish, marlin, shark, tuna) may accumulate significant methylmercury levels. The Food Standards Agency (FSA) advises limiting these species, particularly for pregnant women and young children.
• Occupational exposure: Workers in industries involving mercury — dentistry (amalgam handling), gold mining, chlor-alkali production, fluorescent lamp manufacturing — may require regular biomonitoring.
• Neurological symptoms of unknown cause: Mercury poisoning can present with tremor, memory loss, paraesthesiae (numbness and tingling), visual disturbances, and mood changes. These symptoms may prompt mercury testing.
• Pregnancy planning: Methylmercury crosses the placenta and is neurotoxic to the developing foetus. Women planning pregnancy may wish to know their mercury status, especially if they consume significant amounts of fish.
• Environmental contamination: Communities near mercury-contaminated sites (former industrial works, mines) may be offered screening.
• Dental amalgam concerns: While modern evidence suggests that mercury released from amalgam fillings is within safe limits for most people, some individuals request testing for reassurance or prior to amalgam removal.
• Use of traditional or imported remedies: Certain Ayurvedic, Chinese, and African traditional medicines contain inorganic mercury compounds.

Normal Ranges

Blood mercury is typically measured in micrograms per litre (µg/L) or nanomoles per litre (nmol/L). The following table outlines reference ranges used in the UK:

Category	Blood Mercury (µg/L)	Blood Mercury (nmol/L)	Interpretation
General population (unexposed)	< 5 µg/L	< 25 nmol/L	Normal background level
Regular fish consumers	5–15 µg/L	25–75 nmol/L	Elevated but may reflect dietary intake
Concern threshold	> 20 µg/L	> 100 nmol/L	Investigation and source identification warranted
Occupational guideline (UKHSA)	> 15 µg/L	> 75 nmol/L	Biological monitoring guidance value for workers
Clinical toxicity risk	> 50 µg/L	> 250 nmol/L	Significant risk of neurological effects

The UK Health Security Agency (UKHSA) publishes biological monitoring guidance values for occupational mercury exposure. For the general population, the aim is to keep blood mercury as low as reasonably achievable. There is no established "safe" threshold — adverse effects have been observed at relatively low levels, particularly in developing foetuses and young children.

What Do High Mercury Levels Mean?

Elevated blood mercury indicates recent or ongoing exposure to mercury compounds. Sources and associated conditions include:

• Dietary methylmercury: The most common cause of elevated blood mercury in the general population. Regular consumption of predatory fish — particularly swordfish, shark, marlin, bigeye tuna, and king mackerel — is the primary driver.
• Occupational exposure: Dental workers handling amalgam, industrial workers in mercury-using processes, artisanal gold miners (who use mercury to extract gold from ore), and workers in fluorescent lighting manufacture.
• Environmental contamination: Proximity to contaminated waterways, former chlor-alkali plants, or mercury mining sites.
• Traditional remedies and cosmetics: Mercury-containing Ayurvedic preparations, Chinese medicine pills, and skin-lightening creams sold outside regulated channels.
• Elemental mercury exposure: Broken thermometers, barometers, or mercury spills in the home or workplace. Elemental mercury vapour is efficiently absorbed through the lungs.
• Thimerosal exposure: Thimerosal (ethylmercury) in some vaccines is rapidly excreted and does not accumulate. It contributes negligibly to blood mercury levels and has an excellent safety profile.
• Dental amalgam fillings: Small amounts of mercury vapour are released from amalgam fillings during chewing. For most people, this results in blood mercury levels well within safe limits, though individuals with many fillings may have slightly elevated levels.

Chronic mercury poisoning presents with a classic triad of tremor (fine, intentional tremor of the hands), gingivitis (inflammation of the gums), and erethism (mood disturbance — irritability, anxiety, insomnia, social withdrawal). Methylmercury particularly affects the visual cortex, cerebellar function, and peripheral nerves.

What Do Low Mercury Levels Mean?

Low blood mercury is the desired result and indicates minimal recent exposure. Here is what low-range results suggest:

• Below detection limit (< 1 µg/L): Negligible mercury exposure. This is the ideal result and typical of individuals who eat little or no fish.
• 1–3 µg/L: Normal background level for the UK general population. Consistent with an average British diet that includes moderate fish consumption.
• 3–5 µg/L: Slightly above average but still within the normal range. May reflect regular (but not excessive) consumption of oily fish.
• Declining levels over serial tests: Indicates successful reduction in exposure, whether through dietary modification, occupational controls, or treatment.
• Low levels in pregnancy: Reassuring that foetal methylmercury exposure is minimal.

As with lead, there is no condition caused by mercury "deficiency" — mercury is purely a toxicant with no physiological role. The goal is always to minimise exposure while still obtaining the nutritional benefits of fish consumption.

How to Improve Your Mercury Levels

Since the objective is to reduce mercury levels, improvement means minimising exposure while maintaining a healthy diet:

Dietary Modifications

• Choose low-mercury fish: Salmon, sardines, mackerel (Atlantic), anchovies, herring, trout, and pollock are all excellent sources of omega-3 fatty acids with low mercury content. These should form the basis of your fish consumption.
• Limit high-mercury species: The FSA recommends that pregnant women, women planning pregnancy, and children avoid shark, swordfish, and marlin entirely. Tuna consumption should be limited to four medium cans or two fresh tuna steaks per week.
• Diversify protein sources: Rotate between fish, poultry, legumes, and other proteins to reduce cumulative mercury exposure from any single source.
• Consider selenium-rich foods: Selenium may offer some protection against mercury toxicity by binding to mercury and reducing its bioavailability. Brazil nuts, seafood, and organ meats are rich sources.

Environmental and Occupational Controls

• Safe handling of mercury: Never vacuum a mercury spill (this disperses vapour). Use a commercial mercury spill kit or contact your local authority for disposal guidance.
• Workplace safety: Ensure adequate ventilation, use mercury-free alternatives where possible, and follow occupational health monitoring schedules.
• Avoid mercury-containing products: Choose digital thermometers, LED lighting, and check imported cosmetics and remedies for mercury content.

Medical Management

• Chelation therapy: For significant mercury poisoning, chelating agents such as dimercaptosuccinic acid (DMSA) or dimercaptopropanesulfonic acid (DMPS) may be used under specialist supervision.
• Time: If the source of exposure is removed, blood methylmercury levels halve approximately every 50–70 days through natural excretion.
• Monitoring: Serial blood tests every 3–6 months to confirm declining levels after source removal.

When Should You Get Tested?

Consider a blood mercury test if:

• You eat large predatory fish (swordfish, shark, tuna, marlin) more than twice a week.
• You work in an industry with mercury exposure (dentistry, mining, manufacturing).
• You are pregnant, planning pregnancy, or breastfeeding and consume significant amounts of fish.
• You experience neurological symptoms such as tremor, numbness, tingling, memory loss, or difficulty concentrating.
• You use imported traditional medicines, herbal preparations, or skin-lightening products.
• You have had a mercury spill or environmental exposure incident.
• You are concerned about dental amalgam fillings and their potential mercury contribution.
• A previous test showed elevated levels and you need follow-up monitoring.

Which Lola Health Tests Include Mercury?

Lola Health offers comprehensive health screening that can assess your heavy metal status alongside a wide range of other biomarkers:

• Peak Insights — our most comprehensive test, providing an extensive biomarker profile for a thorough health assessment.
• Vital Check — a broad wellness panel suitable for routine health monitoring and screening.
• Core Health — an essential health check covering key markers for everyday wellbeing.

All Lola Health tests use venous blood draws for clinical-grade accuracy. Your results are reviewed by qualified healthcare professionals who provide personalised recommendations based on your individual profile.