There are strengths and limitations to testing heavy metals in blood and urine matrices, and sensitivity and specificity varies depending upon the specific heavy metal.
Because of the lower concentrations in blood compared with urine, blood arsenic is less sensitive as a biomarker of exposure. Also, the half-time of arsenic in blood is in the order of a few hours compared with a few days in urine. Thus, the time between the last exposure and the sampling can affect the results.
For biomonitoring purposes, to detect long term exposure, urine testing is more sensitive for detection of arsenic.
