Test code: 35417

Clinical use

• Detect cobalt exposure and/or toxicity
• Monitor wear of metal-on-metal hip implants

Clinical background

Cobalt is an element essential for human health as part of vitamin B12 (cobalamin), but is toxic at high levels.1,2 Most people are exposed to unharmful amounts of cobalt compounds in their diet (including from vitamin B12) and in the environment.1,2 People can be exposed to higher levels of cobalt compounds in industrial settings, in areas affected by industrial pollution, and by wear and corrosion of metal hip and knee implants.1,2 Laboratory testing is needed to detect high levels of cobalt in the body that may lead to cobalt toxicity.

Cobalt toxicity can present with a variety of symptoms including polycythemia, hypothyroidism, vision and hearing impairment, and cardiomyopathy. Based on cases reported in the literature, hematologic and endocrine effects are estimated to occur when the concentration of cobalt in blood is over 300 μg/L, while neurological and cardiac effects are estimated to occur at concentrations over 700 μg/L.3 However, symptoms have been reported at lower cobalt levels, likely because of individual factors that increase susceptibility.2,3 Once the source of cobalt exposure is removed, cobalt levels rapidly decrease4 and the symptoms of cobalt toxicity usually improve or resolve.2

Cobalt disseminates systemically and can be detected in urine, serum, and blood. The Cobalt, Blood test (test code 35417) detects cobalt in whole blood. Cobalt levels are most stable in whole blood, which is useful for assessing chronic exposure (eg, from metal implants).2,5 Tests for cobalt in serum (Cobalt, test code 345) and urine (Cobalt, Random Urine, test code 37513; Cobalt, 24-Hour Urine, test code 14761) are also available, which may help assess short-term or occupational exposure, respectively.2

Since cobalt is released from wear and corrosion of metal implants, testing for cobalt in blood also has an adjunctive role in monitoring for malfunctioning metal-on-metal hip implants. However, a cutoff value has not been established, and the sensitivity of blood cobalt testing for detecting malfunctioning implants is modest (52% at a cutoff of 7 μg/L, 63% at 5 μg/L).6 Thus, cobalt testing may be considered for people with symptoms of a malfunctioning metal hip implant, but professional societies indicate that the decision to revise the implant should not be made based on cobalt test results alone.5,6

Interpretive information

A cobalt concentration <1.8 μg/L indicates a normal amount of cobalt exposure.

A cobalt concentration ≥1.8 μg/L indicates high cobalt exposure and risk of systemic toxicity. However, thresholds at which symptoms of cobalt toxicity occur have not been defined.1 Thus, clinical context is important to diagnose cobalt toxicity. This assay does not identify specific cobalt compounds or cobalt sources.

People with metal implants often have elevated systemic levels of cobalt.2 Thresholds for differentiating a malfunctioning implant from normal wear have not been defined, though cutoffs ranging from 5 μg/L to 10 μg/L have been proposed.2,3