Comparison of WHO-UMC and Naranjo Scales for Causality Assessment of Reported Adverse Drug Reactions

The 2 most commonly used scales worldwide are the World Health Organization-Uppsala Monitoring Centre (WHO-UMC) and the Naranjo scales. The present study was planned to assess the degree of agreement between the 2 scales when the same adverse drug reactions (ADR) were assessed by 5 raters independently.

One hundred individual case safety reports were selected randomly from the ADR database of our institute and the details were emailed to 5 different experts (raters), who were DM Clinical Pharmacology residents from different institutes in India. An independent causality assessment of these ADRs was performed independently by these raters using both the WHO-UMC and Naranjo causality assessment scales. The agreement between the 2 scales was assessed for each rater using Cohen κ, and the overall interrater agreement was assessed using Fleiss κ.

The Cohen κ level of agreement between the 2 scales for the 5 raters were substantial, fair, substantial, moderate, and substantial, respectively. The most common causality assessment category as per WHO-UMC scale was "possible" but varied among the raters on the Naranjo scale. No ADR was categorized as "certain" by any rater on the Naranjo scale. The Fleiss κ value for agreement among the 5 raters was found to be 0.2 (slight) for the WHO-UMC scale and 0.297 (fair) for the Naranjo scale.

A moderate level of agreement was observed in this study between the WHO-UMC and Naranjo scales. The level of agreement among these 5 raters was found to be similar for the WHO-UMC and the Naranjo scales, indicating a similar degree of subjectivity for the 2 scales. Hence, more robust and less subjective scales are required for causality assessment.