Heavy Metals Screen Occupational Exposure, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg) are well-known toxins and toxic exposures are characterized by increased urinary excretion of these metals.
Arsenic exists in a number of different forms; some are toxic while others are not. Toxic forms, which are typically encountered as a result of an industrial exposure, are the inorganic species As (+3) (As-III) and As (+5) (As-V) and the partially detoxified metabolites, monomethylarsine and dimethylarsine. The 2 most common nontoxic forms are arsenobetaine and arsenocholine. Arsenic toxicity affects a number of organ systems.
Lead toxicity primarily affects the gastrointestinal, neurologic, and hematopoietic systems.
Chronic exposure to cadmium causes accumulated renal damage.
Mercury is essentially nontoxic in its elemental form. However, once it is chemically modified to the ionized, inorganic species, Hg(++), it becomes toxic. Further bioconversion to an alkyl mercury, such as methyl Hg (CHHg[+]), yields a species of mercury that is highly selective for lipid-rich tissue, such as the myelin sheath, and is very toxic.
Screening potentially exposed workers for heavy metal toxicity in settings where a 24-hour collection is problematic
The reference intervals for this test are Occupational Safety and Health Adminstration (OSHA) thresholds.
The ordering physician will be contacted regarding any result exceeding OSHA thresholds to determine the level of workplace exposure and follow-up action.
Arsenic results exceeding the OSHA threshold will be fractionated to confirm the presence of toxic forms.
Measurement of urine excretion rates either before or after chelation therapy has been used as an indicator of lead exposure. However, blood lead analysis has the strongest correlation with toxicity.
Normally, the excretion of cadmium is proportional to creatinine. When renal damage has occurred, cadmium excretion increases relative to creatinine.
The correlation between the levels of mercury in the urine and clinical symptoms is poor, but urinary mercury is the most reliable way to assess exposure to inorganic mercury.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Nitric acid cannot be added to either the collection or aliquot container. Nitrate interferes with the extraction procedure that would need to take place in the event of a positive arsenic result.
High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium- or iodine-containing contrast media has been administered, a specimen cannot be collected for 96 hours.
This test is intended for use as a screening tool for occupational monitoring. It is not a replacement of HMSU/8633 Heavy Metals Screen, 24 Hour, Urine.
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.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
See individual test descriptions for:
-ASCRU/89890 Arsenic/Creatinine Ratio, Random, Urine
-PBCRU/60247 Lead/Creatinine Ratio, Random, Urine
-CDOM/80595 Cadmium Occupational Monitor, Urine
-HGOM/82755 Mercury Occupational Monitor, Urine