Case Study #3 The Man who Wants to be Tested for Everything

Onset  Patient is a 30 year old male concerned about exposures from neighbor’s gas well and his recent urine results.  Neighbor’s well drilled, not fracked.  No water testing.  Based on patient’s concerns, your covering physician performed a urine heavy metal screen and detected elevated arsenic.  Having searched the internet after learning of his urine results, the patient is concerned that his intermittent R hand numbness, which he now recalls having had recently, is caused by arsenic poisoning

Question  Would you have tested this patient for arsenic?

Answer  Best to identify a specific exposure through environmental testing before considering biomonitoring

History  The patient has been informed by your colleague that his 24 hour urine showed 500 mcg/liter of arsenic, with a lab normal of <35mcg/liter.  He is seeing you in follow-up.  He is concerned bout his hand numbness.  He wants to be chelated.  He wants to be tested for “everything”

Question  Has your patient experience a toxic exposure to arsenic?

Answer  Don’t know yet.  Urine arsenic reflect all sources of arsenic exposure  Organic arsenic from seafood is considered non-toxic  Need to abstain from seafood for 3 or more days prior to testing.  Alternative is to speciate into toxic and non-toxic forms  Also, well water has not been tested

History  Patient has noticed some intermittent R hand numbness for the past few months, which sometimes wakens him at night. No foot numbness.  Otherwise healthy non-smoker. No diabetes, arthritis, or thyroid problems.  Lives alone.  Employed as a mason, with recent overtime.  Enjoys using the internet several hours a day

Exam  Health appearing male.  BP 120/80 P 80  Normal skin, no rashes or lesions.  Positive Tinel’s test over the median nerve in the R wrist

Question  Is your patient’s hand numbness likely to be related to an arsenic exposure?

Answer

Question  Would you consider chelation for this patient

Answer  Chelation rarely used for arsenic toxicity except in acute poisoning

Question  Should he undergo a post-challenge urinary metal test to determine if chelation related to other potential exposures is appropriate?

Answer  It is the position of the American College of Medical Toxicology that post-challenge urinary metal testing has not been scientifically validated, has no demonstrated benefit, and may be harmful when applied in the assessment and treatment of patients in whom there is concern for metal poisoning.”

Question  What about testing for other chemicals in his system?

Answer  Decisions to perform blood or urine tests should be based on environmental testing documenting a potential exposure.  Many substances can be tested for, but often without health based reference ranges to interpret results.  Consider the toxicokinetics of the chemical (1/2 life, excretion route)  Understand the overall sensitivity and specificity of the testing process.  Know in advance how results will influence your treatment or recommendations

Resources  Clinical Practice of Biological Monitoring Harold E. Hoffman et al, OEM Press, 2012  CDC/ATSDR Guidance on the Interpretation and Use of Blood Laboratory Analyses for Volatile Organic Compounds