Approach Considerations
Arsenic screening prior to fractionation
Retrospective data analysis of urine arsenic results from previously tested samples concluded that performing a total arsenic screen before fractionation reduces the number of samples requiring fractionation by more than 91%. [26] A reflex approach of either testing for total arsenic or a heavy metal panel that includes total arsenic can function as a screening test to determine which samples need further evaluation for potential arsenic toxicity. [26]
Laboratory Studies
Obtain a complete blood cell count (CBC) with indices and a reticulocyte count. Microcytic hypochromic anemia is common. Acute hemolytic anemia is characteristic of arsine exposure. Measure serum electrolytes, including calcium and magnesium, particularly in patients with severe vomiting and diarrhea. Type and screen or crossmatch blood for the transfusion in patients exposed to arsine gas.
A test for plasma arsenic concentrations is helpful but rarely available until after the decision to treat is made. Blood arsenic concentrations should not exceed 50 mcg/L. In patients with arsenic poisoning, blood arsenic concentrations commonly range from several hundred to several thousand micrograms per liter. The reported half-life of arsenic in blood immediately following ingestion is in hours, while whole-body clearance may be in days or months and is apparently dose-related.
Urine studies
A 24-hour urine collection for total arsenic excretion can be diagnostic and useful following therapy. A 24-hour clearance of more than 50 mcg is unusual (be sure the patient has not consumed seafood for at least 3 days prior to urine collection). Because nutritional sources of arsenic are not unusual, the laboratory must "speciate" the arsenic into organic and inorganic moieties. The inorganic arsenic is responsible for symptoms and signs of arsenic toxicity. This point is extremely important, since using just the total arsenic level may lead to unnecessary treatment for many patients.
Prior to urine colletion, patients should be instructed to avoid consuming any seafood for at least 7 days. Seafood contains a high concentration of protein-bound arsenic, which is not considered harmful but may lead to an elevated total arsenic level in urine. Elevated urine total arsenic in the setting of recent seafood consumption is unlikely to be clinically meaningful and may lead clinicians down the path of inappropriate treatment.
Various species of arsenic may be recovered in a urine specimen. The human body begins to metabolize inorganic arsenic into various organic forms after a short period of time. Metabolites include methylarsonic acid (MMA) and dimethylarsenic acid (DMA). It should be possible for the laboratory to separate these species from the usual dietary organic forms.
Non-targetted testing, such as urine assays for multiple heavy metals should rarely (if ever) be performed and should be interpreted with caution. Slight elevations above the reference range of urine arsenic are unlikely to represent arsenic poisoningin the absence of clinical signs and symptoms of arsenic toxicity.
Additional urine studies may include the following:
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Obtain a urine pregnancy test in women of childbearing age.
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Obtain a serum acetaminophen level in cases of intentional ingestion.
Imaging Studies
An abdominal radiograph may reveal the presence of radio-opaque densities and may resemble an upper GI series. [27]
Other Tests
Nerve conduction studies may confirm the peripheral neuropathy. This may be particularly important because the classic stocking-glove distribution suggests another etiology.
Cardiac arrhythmias and, in rare cases, cardiac failure have been reported as resulting from arsenic toxicity. Electrocardiography is therefore indicated.
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"Blackwater" urine due to massive hemolysis, from a patient exposed to arsine at a gas tank cleaning operation.
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Mees lines, or leukonychia, are transverse white bands with no palpable ridges that appear on the fingernails as a result of arsenic poisoning, certain cancers, and treatment with certain chemotherapy agents. Courtesy of Wikimedia Commons (Author Yannick Trottier) (https://commons.wikimedia.org/wiki/File:Mees%27_lines.jpg).
