Comparison of the Liverpool Causality Assessment Tool vs. the Naranjo Scale for predicting the likelihood of an adverse drug reaction: A retrospective cohort study.

Aims: The aim of this study is to compare the Liverpool Causality Assessment Tool vs. Naranjo Scale for screening suspected adverse drug reaction (ADR) cases.

Methods: We retrospectively reviewed patient charts with a history of suspected ADR, scored using both tools, and determined how each correlates with laboratory and other investigations. A total of 924 charts from the Clinical Pharmacology Clinic at the London Health Sciences Centre were reviewed, and 529 charts contained objective findings to support or against the diagnosis of ADR. The participant age ranged from 1 month to 93 years. We determined that the sensitivity (SN) and specificity (SP) of Liverpool and Naranjo tools for predicting ADRs with scores ranging from Possible to Definite were considered positive and Unlikely/Doubtful as negative for ADR. These results were confirmed by laboratory or clinical (re-challenge) testing in 529 cases.

Results: Liverpool causality tool had SN of 97.2 ± 2.4% and SP of 2.3 ± 1.57%. The positive (PPV) and negative predictive values (NPV) were 34.1 and 61.5%, respectively. The Naranjo Scale had SN of 81.2 ± 5.69% and SP of 13.2 ± 3.56%. PPV and NPV were 32.7 and 57.5%, respectively.

Conclusion: The Liverpool Causality Assessment Tool is a more sensitive tool than the Naranjo Scale in the assessment of possible ADRs, but both tools have poor SP. The Liverpool Tool can be a useful screening tool in settings where other tests may not be readily available. However, the low PPV and NPV of both tools suggest that to pursue further testing is needed to confirm or deny an ADR.