A positive cobalt spot test falsely indicating an occupational allergic contact dermatitis caused by cobalt

For investigation of chemical exposure in allergic individuals, spot tests are invaluable. A reagent may react with a specific compound to give a specific typical colour, and thus indicate the presence of the specific substance. Spot tests can give both false-negative and false-positive reactions. To confirm the presence of the substance and quantify it, more sophisticated methods are required. On the basis of a positive cobalt spot test result, a woman was initially diagnosed with an occupational allergic contact dermatitis caused by cobalt.

To investigate cobalt release from three different metal weaves to which our patient was occupationally exposed.

The cobalt gel test and atomic absorption spectroscopy (AAS) were used to investigate the metal weaves. Two types of extract based on artificial sweat and nitric acid, respectively, were investigated with AAS.

No cobalt release was demonstrated with AAS.

When a diagnosis of allergic contact dermatitis caused by a sensitizer based on a positive spot test result will have far-reaching consequences, such as change of work, retraining, and claim on and payment of worker's compensation, conformational analysis must be performed.