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Arsenic, Urine

Measures how much arsenic is in a single urine sample, a common first test for recent arsenic exposure.

AI-verified against cited sources. Awaiting expert reviewLOINC 5586-3

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What it is

Arsenic is a natural element found in soil, rock and some drinking water. It also shows up in certain jobs, wood treatments and foods. Your body clears most arsenic through the urine within a few days, so this test shows recent exposure. The result is the concentration in one sample, in µg/L. It counts all forms of arsenic, including the mostly harmless kind found in seafood. A 24-hour version and a creatinine-corrected version are separate tests.

Why it matters

Long-term exposure to inorganic arsenic, mostly from drinking water or some workplaces, is linked to skin changes, nerve and heart problems and a higher chance of some cancers. A urine test shows whether arsenic is getting into your body. It can't tell you whether it will affect your health. Your clinician reads it together with your diet, water source, job and symptoms.

If it’s high

A result above your lab's limit means more arsenic than usual left your body in that sample. The most common reason is eating seafood or seaweed, which contain a form of arsenic that is much less harmful. A total arsenic result can't tell the forms apart, so labs often run a second test (called speciation) when the number is above a set cutoff (Mayo uses 10 µg/L). Well water, some workplaces and some remedies can also raise it. Your clinician can put the number in context.

Common causes

  • Eating fish, shellfish or seaweed in the last few days (mostly the less toxic organic arsenic)
  • Drinking water from a private well or an area with naturally high arsenic
  • Work with arsenic, such as smelting, wood treating or pesticide use
  • Sawdust or smoke from burning wood treated with arsenic
  • Some folk, imported or alternative remedies
  • A very concentrated (dark) urine sample

What can help

  • Ask your clinician whether to follow up with an arsenic speciation test, or a repeat after a few days without seafood
  • Talk through possible sources with your clinician, such as well water, your job, hobbies, wood stoves or treated wood
  • If you have a private well, ask your local health department how to have the water tested

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 35 µg/L. Source: Mayo Clinic Laboratories (catalog mirrored at testcatalog.org), ATSDR (archived copy), Journal of Medical Toxicology.

What can affect your result

  • Seafood and seaweed in the 2 days before the sample
  • Recent contrast dye (gadolinium or iodine), which can disrupt the measurement for about 4 days
  • How dilute or concentrated your urine is
  • Timing within the work week, for work-related testing
  • Your water source, diet and job
  • Seafood and seaweed in the 2 days before the sample can add harmless organic arsenic to the total. Mayo asks for no seafood for 48 hours before collection.
  • Gadolinium or iodine contrast dye can interfere with this kind of metal test. Mayo advises not collecting urine for 96 hours after a dose.
  • How diluted your urine is changes the number. A very watery sample can read low and a concentrated one high, which is why labs also report arsenic per gram of creatinine.
  • Use the clean plastic container your lab gives you. Mayo specifies no metal cap and no glued insert.
  • Urine collected after taking a chelating medicine (a "provoked" test) has no valid reference range and is not recommended for diagnosis.

A single (random) urine sample. For work-related testing, Mayo's occupational limit applies to a sample taken at the end of the work week. Shows arsenic taken in over roughly the last few days. Urine levels can fall quickly in the first 1 to 2 days after a single large exposure.

When to talk to a clinician

Contact your clinician promptly if your result is well above your lab's range and you have symptoms such as nausea, vomiting, belly pain, numbness or tingling in your hands or feet, or new skin changes. If you may have swallowed or breathed in a large amount of arsenic, call Poison Control at 1-800-222-1222 in the US, or your local emergency number, right away.

Questions you could ask

  • What should I avoid eating or doing before this test?
  • How does my lab's range apply to my result?
  • Could seafood, my drinking water or my job explain this result?
  • Should we repeat the test after a few days without seafood, or ask for arsenic speciation?
  • Would a 24-hour collection or a creatinine-corrected result be more useful?

Questions people ask

My result is high, but I eat a lot of seafood. What does that mean?

Fish, shellfish and seaweed contain an organic arsenic that is mostly harmless and leaves the body within about 2 days. Because this test counts it, a high total can be from seafood. Your clinician may ask for a repeat after a few seafood-free days, or for a speciation test that separates the forms.

What is the difference between total and speciated arsenic?

Total arsenic adds up every form. Speciation measures the forms separately, so the toxic inorganic and methylated forms can be told apart from the harmless seafood form. Mayo compares the toxic forms with a 35 µg/L limit.

Show the science and sources

Units

  • 1 µg/L = 1 µg/L
  • 1 µg/L = 1 ng/mL
  • 1 µg/L = 13.35 nmol/L
  • 1 µg/L = 0.01335 µmol/L

Open the Arsenic (urine) unit converter

For clinicians and researchers

Total urinary arsenic includes inorganic arsenic (arsenite and arsenate), its methylated metabolites (MMA and DMA) and organic seafood arsenic such as arsenobetaine, which is excreted unchanged within about 48 hours. Mayo measures total arsenic by ICP-MS/MS and reflexes to speciation (ion chromatography ICP-MS) at 10 mcg/L or more. Its "toxic arsenic" limit of <35 mcg/L, the sum of inorganic and methylated species, rests on the ACGIH Biological Exposure Index. ATSDR treats total arsenic above 100 µg/L as abnormal and notes that some studies suggest slight health risks above 50 µg/L. In NHANES 2003-2004 (ages 6 and up), the 95th percentile was 65.4 µg/L for total urinary arsenic and 18.9 µg/L for the sum of inorganic-related species. A sample under 20 µg/L likely has little organic contribution. The half-life of inorganic arsenic is about 10 hours. Gadolinium and iodine contrast interfere with ICP-MS metal assays. Chelator-provoked urine has no established reference range (Ruha 2013). Creatinine-corrected and 24-hour results are separate markers.

LOINC 5586-3 (primary), 30924-5, 15115-9. Specimen: urine.

Sources

  1. Arsenic Speciation, Random, Urine (Mayo test SPAS), Mayo Clinic Laboratories (catalog mirrored at testcatalog.org)
  2. Arsenic Occupational Exposure, with Reflex, Random, Urine (Mayo test ASUOE), Mayo Clinic Laboratories (catalog mirrored at testcatalog.org)
  3. Arsenic Toxicity: Clinical Assessment (Case Studies in Environmental Medicine), ATSDR (archived copy)
  4. Recommendations for provoked challenge urine testing, Journal of Medical Toxicology (2013)
  5. Arsenic (PubChem compound 5359596), 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.

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