Arsenic (Total Organic and Inorganic)
|Clinical Use:||Used for the detection of chronic (occupational) or very recent arsenic exposure|
|Background:||Arsenic (As) exists in a number of toxic and nontoxic forms. The toxic forms are the inorganic species As(+5), also denoted as As(V), the more toxic As(+3), also known as As(III), and their partially detoxified metabolites, monomethylarsine (MMA) and dimethylarsine (DMA). Detoxification occurs in the liver as As(+3) is oxidized to As(+5) and then methylated to MMA and DMA. As a result of these detoxification steps, As(+3) and As(+5) are found in the urine shortly after ingestion, whereas MMA and DMA are the species that predominate more than 24 hours after ingestion.
Blood concentrations of arsenic are elevated for a short time after exposure, after which arsenic rapidly disappears into tissues because if its affinity for tissue proteins. The body treats arsenic like phosphate, incorporating it wherever phosphate would be incorporated. Arsenic “disappears” into the normal body pool of phosphate and is excreted at the same rate as phosphate (excretion half-life of 12 days). The half-life of inorganic arsenic in blood is 4 to 6 hours, and the half-life of the methylated metabolites is 20 to 30 hours. Abnormal blood arsenic concentrations (>12 ng/mL) indicate significant exposure, but will only be detected immediately after exposure.
Arsenic is not likely to be detected in blood specimens drawn more than 2 days after exposure because it has become integrated into nonvascular tissues. Consequently, blood is not a good specimen to screen for arsenic, although periodic blood levels can be determined to follow the effectiveness of therapy. A wide range of signs and symptoms may be seen in acute arsenic poisoning including headache, nausea, vomiting, diarrhoea, abdominal pain, hypotension, fever, haemolysis, seizures, and mental status changes.
Symptoms of chronic poisoning, also called arseniasis, are mostly insidious and nonspecific. The gastrointestinal tract, skin, and central nervous system are usually involved. Nausea, epigastric pain, colic (abdominal pain), diarrhoea, and paresthesias of the hands and feet can occur.
|Reference Ranges:||Total urine arsenic: 0 – 174 umol/mol creatinineOccupational exposure range for inorganic arsenic: 0 – 40 umol/mol creatinine
Normal background range for inorganic arsenic and metabolites: 0 – 10 umol/mol creatinine
* Note that if inorganic arsenic is specifically requested the sample requirements are the same but the general population reference range – 0 – 10 umol/mol creat- for non-occupational exposure will be reported by referral lab.
|Patient Preparation:||Seafood containing non-toxic organo-arsenic compounds should be excluded from diet for 5 days prior to sampling.|
|Specimen Requirements:||Random urine sample, 20ml in a plain container|
|Turnaround Time:||4 weeks|
|Referred Test:||Referred test|
|Location:||Health and safety laboratory|