Thallium Toxicity Workup

  • Author: G Patrick Daubert, MD; Chief Editor: Asim Tarabar, MD   more...
 
Updated: Apr 11, 2011
 

Laboratory Studies

  • Because laboratory studies are generally nonspecific, any unexplained peripheral neuropathy, especially accompanied by alopecia, should raise clinical suspicion for thallium toxicity. In consultation with the medical toxicologist, initiate treatment of patients with high suspicion of thallium toxicity while awaiting laboratory confirmation.
  • The definitive clinical diagnosis of thallium poisoning can only be established by demonstrating elevated thallium levels. Thallium can be recovered in the hair, nails, feces, saliva, blood, and urine.
  • A 24-hour urine thallium concentration is the standard toxicologic method and is assayed by atomic absorption photospectrometry. The normal level is less than 5 mcg/L.
  • A urine spot test can deliver faster results. However, it often gives false-positive results, and it requires the use of 20% nitric acid, which can be dangerous and is usually not readily available.
  • Because it is rapidly eliminated from the body, measurements of blood thallium reflect only recent exposures. Thus, it is not generally considered to be a reliable means of identifying or monitoring exposure to thallium.
  • A CBC with differential can identify anemia, leukocytosis, eosinophilia, and thrombocytopenia, which have all been reported in cases of thallium exposure. Anemia most likely occurs secondary to GI hemorrhage.
  • Electrolytes, calcium, glucose, BUN, creatinine, and liver function tests (LFTs) should be obtained. Thallium exposure can lead to electrolyte and glucose abnormalities, hypocalcemia, and impair renal and hepatic dysfunction.
  • A pregnancy test should be considered for all women of childbearing age.
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Imaging Studies

  • Thallium is radiopaque; therefore, an abdominal radiograph should be obtained. This may reveal thallium metal after an acute ingestion. Radiographs of suspected exposure sources may be useful for confirming the presence of a heavy metal.
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Other Tests

  • Nerve conduction studies (NCS) may reveal findings consistent with an axonal sensorimotor peripheral neuropathy, with nerves innervating the feet most significantly involved. NCS may be useful in both diagnosing and monitoring patients with thallium exposure. The severity of abnormalities on NCS has been shown to correlate with the severity of other symptoms and findings.
  • An EEG may show nonspecific slow-wave activity in severe cases.
  • Microscopic inspection of scalp hair reveals dark black and brown pigment in the hair roots in approximately 95% of poisoned patients. However, this may be difficult to visualize by the untrained observer. Darkening of the hair root can occur as early as 4 days postexposure. These dark regions are an optical phenomenon caused by the accumulation of gaseous inclusions that diffract the light, resulting in the appearance of a black band.
  • Electroretinographic (ERG) examination reveals a delayed visual evoked response. These ERG changes tend to occur before development of clinical symptoms in thallium intoxication. ERG may be useful when persons with known thallium exposure receive follow-up examinations.[17]
  • An ECG should be obtained to identify tachycardia and cardiac arrhythmias.
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Contributor Information and Disclosures
Author

G Patrick Daubert, MD  Assistant Professor, Assistant Medical Director, Sacramento Division, California Poison Control System; Director of Clinical and Medical Toxicology Education, Department of Emergency Medicine, University of California, Davis Medical Center

G Patrick Daubert, MD is a member of the following medical societies: American College of Emergency Physicians, American College of Medical Toxicology, American Medical Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

William K Chiang, MD  Associate Professor, Department of Emergency Medicine, New York University School of Medicine; Chief of Service, Department of Emergency Medicine, Bellevue Hospital Center

William K Chiang, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American College of Medical Toxicology, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Senior Pharmacy Editor, eMedicine

Disclosure: eMedicine Salary Employment

John G Benitez, MD, MPH, FACMT, FAACT, FACPM, FAAEM,  Associate Professor, Department of Medicine, Medical Toxicology, Vanderbilt University Medical Center; Managing Director, Tennessee Poison Center

John G Benitez, MD, MPH, FACMT, FAACT, FACPM, FAAEM, is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Medical Toxicology, American College of Preventive Medicine, Society for Academic Emergency Medicine, Undersea and Hyperbaric Medical Society, and Wilderness Medical Society

Disclosure: Nothing to disclose.

John D Halamka, MD, MS  Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center

John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Asim Tarabar, MD  Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital

Disclosure: Nothing to disclose.

References

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