Mercury, Blood
Total mercury in whole blood, which mostly reflects methylmercury from fish and shellfish and any recent exposure.
AI-verified against cited sources. Awaiting expert reviewAlso called B-HgLOINC 5685-3
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What it is
Mercury is a metal that exists in several forms. The form in fish, called methylmercury, is absorbed easily and shows up in the blood, so this test mostly reflects how much fish and shellfish you have eaten recently. Blood mercury also rises after recent contact with other forms, such as vapor from a spill. The lab measures total mercury in a whole-blood sample.
Why it matters
Mercury, especially methylmercury, can affect the nervous system, and a developing baby's brain is the most sensitive. That is why blood mercury is often checked before or during pregnancy in people who eat a lot of fish. Fish also provides useful nutrients, so ask your clinician how to choose lower-mercury options if your level is higher.
If it’s high
A higher level most often comes from eating fish and shellfish, especially larger, longer-lived fish. It can also come from recent contact with other forms of mercury. Higher levels matter most during pregnancy and breastfeeding. The same number can be unimportant for one person and worth discussing for another.
Common causes
- Frequent fish and shellfish meals, especially larger predatory fish that FDA advice lists as highest in mercury, such as swordfish, shark, king mackerel, bigeye tuna and Gulf of Mexico tilefish
- A sample contaminated by skin, dust or a tube that was not trace-element-free
- Contact with liquid mercury or vapor at work or from a spill
- Some skin-lightening creams and traditional remedies that contain mercury
What can help
- Ask your clinician which fish and portion sizes fit your situation, especially if you are pregnant, planning pregnancy or feeding a young child
- Look back at which kinds of fish you eat most often
- Ask whether a urine mercury test would add information about other forms of mercury
- Ask whether to repeat the test in a certified trace-element-free tube if contamination is possible
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: up to 10 µg/L. Source: Mayo Clinic Laboratories (via the testcatalog.org mirror), ARUP Laboratories, Environmental Health Perspectives.
- Adults (this one applies)up to 10 µg/L
Sources: Mayo Clinic Laboratories (via the testcatalog.org mirror), ARUP Laboratories, Environmental Health Perspectives
See Blood Mercury by age and sex, with the U.S. survey numbers where they exist.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Blood Mercury by age and sex: every percentile as a table, with a download.
What can affect your result
- How much fish and shellfish you eat, and which kinds
- Seafood in the 2 to 3 days before the draw
- Pregnancy, which is when the result is most often used
- Recent contrast dye (gadolinium or iodine)
- Work or home exposure to liquid mercury or vapor
- The tube used and how the sample was handled
- Fish and shellfish in the days before the draw raise blood mercury. ARUP asks you to avoid seafood for 48 to 72 hours before testing; ask your clinician whether you should follow that or eat as usual.
- Gadolinium or iodine contrast dye can interfere with this kind of metal test. Mayo Clinic Laboratories asks for a 96-hour wait after contrast.
- A sample drawn into a tube that is not certified trace-element-free, or contaminated by skin, can read falsely high.
- Mercury is volatile, and the concentration in a stored sample may fall over time.
- ARUP lists diet, supplements, vitamins and minerals as possible sources of interference. Ask your clinician before stopping anything.
Blood mercury mostly reflects recent exposure. According to ARUP it rises sharply and falls over several days after ingestion, and changes from regular fish intake can take weeks to show.
When to talk to a clinician
Talk with your clinician soon if your result is above your lab's range, especially if you are pregnant or planning pregnancy. ARUP notes that unexposed people rarely go above 20 µg/L, and that poisoning with organic mercury can include slurred speech, poor balance and narrowed vision at blood levels of 20 to 50 µg/L. Seek urgent care for new numbness, balance or vision changes, or confusion after a known heavy mercury exposure.
Questions you could ask
- Which fish and portion sizes make sense for me?
- Could fish be the main source, or should we look at other sources too?
- Would a urine mercury test or a repeat blood test add anything?
- Does my result matter for a current or future pregnancy?
Questions people ask
Should I avoid fish before this test?
ARUP asks people to avoid fish and shellfish for 48 to 72 hours before the draw. If the goal is to see your usual fish-related exposure, ask your clinician whether to follow that or eat as you normally do.
Which is better, a blood or a urine mercury test?
It depends on the question. According to ARUP, blood is preferred for recent or acute exposure and urine for long-term exposure to elemental or inorganic mercury. Mercury from fish (methylmercury) shows up mostly in blood.
My lab's upper limit is 10 µg/L, but I have seen lower numbers. Why?
Labs set one upper limit for everyone, near 10 µg/L. Researchers also use lower comparison values for pregnancy. In US survey studies, 5.8 µg/L is used as the level above which exposure before birth is considered a concern. Ask your clinician which number matters for you.
Show the science and sources
Units
- 1 µg/L = 1 µg/L
- 1 µg/L = 0.1 µg/dL
- 1 µg/L = 4.985 nmol/L
Open the Blood Mercury unit converter
For clinicians and researchers
Total mercury in whole blood by ICP-MS (triple-quadrupole at Mayo Clinic Laboratories, ICP-MS at ARUP), reported in µg/L (ng/mL at Mayo). Both labs use an upper limit of about 10 µg/L. ARUP states that blood mercury mostly reflects recent exposure, rises sharply and falls quickly over several days after ingestion, and is the preferred test for acute exposure, with urine preferred for chronic elemental or inorganic exposure. ARUP's interval relates to inorganic mercury, and dietary or nonoccupational exposure to organic mercury raises the total. Methylmercury and inorganic mercury can be measured separately by speciation tests. In the 1999 to 2000 NHANES, blood methylmercury in 1,709 US women had a median of 0.6 µg/L and a 95th percentile of 6.7 µg/L; blood mercury was about seven times higher in women who ate nine or more fish or shellfish meals in the past 30 days than in women who ate none, and a value of 5.8 µg/L or higher was used as the level above which exposure was considered to carry increased neurodevelopmental risk (Mahaffey 2004). Samples need a royal blue K2EDTA or sodium heparin trace-element-free tube, and mercury can be lost from stored specimens.
LOINC 5685-3 (primary), 25170-2. Specimen: whole-blood.
Sources
- Heavy Metals Screen with Demographics, Blood (test HMDB), Mayo Clinic Laboratories (via the testcatalog.org mirror)
- Mercury, Whole Blood (test 0099305), ARUP Laboratories
- Blood organic mercury and dietary mercury intake: National Health and Nutrition Examination Survey, 1999 and 2000, Environmental Health Perspectives (2004)
- Advice About Eating Fish, U.S. Food and Drug Administration and EPA
- Mercury (compound summary), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.