A false positive for clozapine using high‐pressure liquid chromatography with ultraviolet detection

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Background: We report a case of a false positive for clozapine, when analysing serum levels using a high‐pressure liquid chromatography with ultraviolet (HPLC‐UV) detection method.

Methods: A patient not taking clozapine tested positive for clozapine three times in two different samples. This false positive was discovered by chance, because of an administrative error made in the first analytic test request.

Results: The analysis of the first sample with a more specific method [HPLC‐tandem mass spectrometry (LC‐MS/MS)] showed that no clozapine was present.

Conclusions: It is important to acknowledge that depending on the method employed, a false positive should not be ruled out as a possibility. Moreover, and even more worryingly, it should also be taken into account that clozapine serum levels could be tested erroneously high if the unknown interference is present and the HPLC‐UV method is used. Although the interfering compound could not be identified, the possibility of a cross‐reaction when analysing serum clozapine levels with the HPLC‐UV method warrants urgent attention.

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1601-5215.2012.00637.x

Affiliations: 1: Pharmacy Service, Red de Salud Mental de Araba, C/alava 43, 01006 Vitoria-Gasteiz, Araba, Spain 2: Communitary Rehabilitation Centre, Red de Salud Mental de Araba, C/reyes católicos 6, 01006 Vitoria-Gasteiz, Araba, Spain 3: Pharmacy Service, Hospital Alto Deba, Avda, Nafarroa 16, 20500 Arrasate Gipuzkoa, Spain 4: Reference Laboratory S.A., Barcelona, Spain

Publication date: August 1, 2012

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