The priority symptom to report for a patient taking rituximab is:
C. Shortness of breath
Shortness of breath can be a serious side effect of rituximab and may indicate a potentially life-threatening condition such as an infusion reaction or lung problems. It is crucial to report this symptom promptly so that appropriate medical attention and intervention can be provided. While the other symptoms (nausea, fatigue, and hair loss) are also possible side effects of rituximab, shortness of breath takes precedence due to its potential severity.