Never on a Saturday (or a Sunday): the case against using weekend urine specimens to assess arsenic exposure

The Wisconsin Department of Health and Family Services Bureau of Public Health recently investigated two cases of suspected arsenic poisoning. These cases involved four adults whose urinary arsenic levels ranged from 340 to 1485 ug/L (normal 0-30 ug/L). These findings were initially interpreted as evidence of an ongoing exposure to a toxic form of arsenic, however follow-up investigations determined that all of the urine specimens had been collected on a weekend and that each of these individuals had consumed fish within 48-hours of urine collection. Most of the fish was consumed at "Friday night fish fries" which are a popular tradition at many local restaurants. Urine samples collected after these individuals eliminated fish from their diets contained normal arsenic levels. This report suggests the need for laboratories to differentiate non-toxic forms of arsenic that are present in fish and seafood products from other species of this element. Until more specific analytical methods become available, patients should be instructed to omit fish and seafood from their diets for several days prior to collecting urine for arsenic analysis. In addition, elevated urinary arsenic levels should be interpreted cautiously and exposure to toxic forms should be confirmed before a diagnosis of arsenic poisoning is entertained.