Heavy metal is a broad term that describes a group of naturally occurring metallic elements of high molecular weight and density compared to water. At low concentrations, certain heavy metals, such as iron, zinc, copper, and manganese, are essential for human survival but can become toxic agents at higher concentrations. Other heavy metals, such as arsenic, cadmium, lead, thallium, and mercury, serve no biological role. However, they will inevitably enter the human body due to their presence in the environment. Similarly to essential metals, they induce toxicity once specific concentrations are reached.
Confirming the diagnosis of elemental toxicity is challenging as signs and symptoms are similar to those of many non-element-dependent diseases. Diagnosis of elemental toxicity requires demonstration of all of the following factors: (1) a source of elemental exposure must be evident, (2) the patient must demonstrate signs and report symptoms typical of the element, and (3) abnormal element concentration in the appropriate tissue must be evident. If one of these features is absent, one cannot make a conclusive diagnosis of elemental toxicity. The laboratory plays a vital role in this process, and appropriate specimen collection coupled with accurate analysis can aid in correct diagnosis.
In clinical practice, analysis of toxic elements should always be considered in the clinical work-up of the patient with (1) renal disease of unexplained origin, (2) bilateral peripheral neuropathy, (3) acute changes in mental function, (4) acute inflammation of the nasal or laryngeal epithelium, or (5) a history of elemental exposure.
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