Skip to content
Blood Test Tracker

Arsenic/Creatinine Ratio, Urine

Arsenic in a single urine sample, divided by creatinine to adjust for how dilute the urine is.

AI-verified against cited sources. Awaiting expert reviewLOINC 13463-5

Check your result

Sex (optional)

Type your result to see where it falls.

Nothing you type here leaves your browser.

What it is

Arsenic is a natural element found in soil, rock and some drinking water. Your body clears most of it through the urine within a few days. Urine can be watery or concentrated depending on how much you have had to drink, which changes the arsenic number. Creatinine is a waste product that your body releases at a steady rate. Dividing arsenic by creatinine evens out that effect, so results from different samples are easier to compare. The result counts all forms of arsenic, including the mostly harmless kind found in seafood.

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. This 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, relative to the creatinine in the 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 high. 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

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 24 µg/g creatinine. 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
  • Your water source, diet and job
  • Your creatinine level, which depends on muscle mass and how dilute the sample is
  • Age: Mayo has only set an adult range (18 and older)
  • 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.
  • Very dilute or very concentrated urine can make the creatinine part of the ratio less reliable.
  • 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. Mayo does not ask for a particular time of day. Shows arsenic taken in over roughly the last few days.

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 be more useful?

Questions people ask

Why is arsenic divided by creatinine?

A single urine sample can be watery or concentrated, which moves the arsenic number up or down. Creatinine is released at a fairly steady rate, so dividing by it adjusts for how dilute the sample is.

Can I convert µg/g creatinine to µg/L?

Only if you know the creatinine in the same sample. Arsenic in µg/L equals the ratio in µg/g multiplied by creatinine in g/L, which is creatinine in mg/dL divided by 100.

Show the science and sources

Units

  • 1 µg/g creatinine = 1 µg/g creatinine
  • 1 µg/g creatinine = 0.1131 µg/mmol creatinine

Open the Arsenic/creatinine unit converter

For clinicians and researchers

Mayo measures urine arsenic by ICP-MS/MS and creatinine by an enzymatic colorimetric assay, then reports the ratio, with reflex to speciation when total arsenic is 10 mcg/L or more. ATSDR notes that dividing the arsenic concentration by grams of creatinine adjusts for urine dilution or concentration, and that a 24-hour collection reflects true excretion more accurately; not all labs make the creatinine adjustment. Total urinary arsenic includes inorganic arsenic, methylated metabolites (MMA, DMA) and organic seafood arsenic such as arsenobetaine, which clears within about 48 hours. Creatinine correction is less reliable in very dilute or very concentrated samples and in people with unusually high or low creatinine excretion. Gadolinium and iodine contrast interfere with ICP-MS metal assays. Chelator-provoked urine has no established reference range (Ruha 2013). The µg/L concentration and the 24-hour amount are separate markers.

LOINC 13463-5 (primary), 56652-1. Specimen: urine.

Sources

  1. Arsenic/Creatinine, Ratio, with Reflex, Random, Urine (Mayo test ASUCR), Mayo Clinic Laboratories (catalog mirrored at testcatalog.org)
  2. Arsenic Toxicity: Clinical Assessment (Case Studies in Environmental Medicine), ATSDR (archived copy)
  3. Recommendations for provoked challenge urine testing, Journal of Medical Toxicology (2013)
  4. Creatinine (PubChem compound 588), 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.

Related markers