Test Catalog

Test ID: ASFRU    
Arsenic Fractionation, Random, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of arsenic intoxication in random urine specimens

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Total arsenic will be performed first. If the total arsenic concentration is 15 mcg/L or greater, then fractionation will be performed and reported.  If total arsenic is below 15 mcg/L, total arsenic will be reported as less than 15 mcg/L and fractionation will not be performed.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Arsenic (As) exists in a number of different forms; some are toxic, while others are not. The toxic forms are the inorganic species of As(+3) (As-III), As(+5) (As-V), and their partially detoxified metabolites, monomethylarsine, and dimethylarsine. As-III is more toxic than As-V and both are more toxic than mono- and dimethylarsine. The biologic half-life of inorganic arsenic is 4 to 6 hours, while the biologic half-life of the methylated metabolites is 20 to 30 hours. Target organs of As-III-induced effects are the heart, gastrointestinal tract, skin and other epithelial tissues, kidney, and nervous system.


Inorganic arsenic is carcinogenic to humans. Symptoms of chronic poisoning, called arseniasis, are mostly insidious and nonspecific. The gastrointestinal tract, skin, and central nervous system are usually involved. Nausea, epigastric pain, colic abdominal pain, diarrhea, and paresthesias of the hands and feet can occur.


Nontoxic, organic forms of arsenic are present in many foods. Arsenobetaine and arsenocholine are the 2 most common forms of organic arsenic found in food. The most common foods that contain significant concentrations of organic arsenic are shellfish and other predators in the seafood chain (cod, haddock, etc). Some meats, such as from chickens that have been fed on seafood remnants, may also contain the organic forms of arsenic.


Following ingestion of arsenobetaine and arsenocholine, these compounds undergo rapid renal clearance to become concentrated in the urine. Organic arsenic is completely excreted within 1 to 2 days after ingestion and there are no residual toxic metabolites. The biologic half-life of organic arsenic is 4 to 6 hours.


For reporting purposes, the concentrations of the inorganic forms (As[+3] and As[+5]) along with the methylated forms (monomethylarsine and dimethylarsine) will be summed and reported together as 'Inorganic' arsenic. This is consistent with how the biological exposure index (BEI) reference range is reported.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


<20 mcg/L



<20 mcg/ L


Reference values apply to all ages.


*Biological exposure indices (BEI) for arsenic is 35 mcg/L based on the concentration of inorganic arsenic plus methylated metabolites.

Interpretation Provides information to assist in interpretation of the test results

The quantitative reference range for fractionated arsenic applies only to the inorganic forms. Concentrations of 20 mcg inorganic arsenic per liter or higher are considered toxic.


There is no limit to the normal range for the organic forms of arsenic, since they are not toxic and are normally present after consumption of certain food types. For example, a typical finding in a urine specimen with total 24-hour excretion of arsenic of 350 mcg/24 hours would be that more than 95% is present as the organic species from a dietary source, and less than 5% is present as the inorganic species. This would be interpreted as indicating the elevated total arsenic was due to ingestion of the nontoxic form of arsenic, usually found in food.


A normal value for blood arsenic does not exclude a finding of elevated urine inorganic arsenic, due to the very short half-life of blood arsenic.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Consumption of seafood before collection of a urine specimen for arsenic testing is likely to result in a report of an elevated concentration of arsenic, which can be clinically misleading.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Caldwell KL, Jones RL, Verdon CP, et al: Levels of urinary total and speciated arsenic in the US population: National Health and Nutrition Examination Survey 2003-2004. J Expo Sci Environ Epidemiol 2009;19:59-68

Special Instructions Library of PDFs including pertinent information and forms related to the test