Thallium

Thallium is a colorless, odorless and tasteless metal that is rapidly absorbed after skin contact, inhalation or ingestion. Thallium poisoning occurs worldwide and is usually caused by accidental contamination of grain or rice, intentional adulteration of food, and occupational exposures. Thallium is a byproduct of lead smelting. Thallium is present in some rodenticides, depilatories, photoelectric cells, lamps, semiconductors and scintillation counters. Thallium toxicity is largely due to its displacement of potassium in ion channels, which inhibits cellular function.

The earliest signs of thallium toxicity include abdominal pain and vomiting. Later signs include painful paresthesia, ptosis, nystagmus, ataxia, choreoathetosis, memory loss, delirium and renal failure. Alopecia may occur within 3 weeks are exposure. High dose exposure can be fatal.

Thallium can be detected on radiographs of the abdomen because it is radiopaque. The diagnosis of thallium exposure is confirmed by detecting elevated levels in plasma and urine by inductively coupled plasma mass spectrometry. 

Reference range for urine thallium is less than 2 micrograms per 24 hours. Patients exposed to thallium can have urine concentrations greater than 10 microgram per day.

Reference range for blood thallium levels is less than 2 nanograms per mL. Thallium concentrations greater than 10 ng/mL are considered significant exposures. 

Specimen requirement is a 24 hour urine collection or a Royal blue-top tube (metal free) of blood. Patients who have received gadolinium or iodine contrast media should wail at least 96 hours before collecting a specimen. 

References

Ibrahim D, et al. Heavy metal poisoning: clinical presentations and pathophysiology. Clin Lab Med 2006;26:67-97

Zhao G, Ding M, Zhang B, et al: Clinical manifestations and management of acute thallium poisoning. Eur Neurol 2008;60:292-297.

Pelcloval D, et al. Two-year follow-up of two patients after severe thallium intoxication. Hum Exper Toxicol. 2009;28(5):263-272.

Zavaliy LB, et al. Diagnosis and treatment of persons with acute thallium poisoning. Toxicol Rep. 2021;8:277-281.