A method is provided for determining the severity of appendicitis in a patient that includes testing a blood, serum or plasma sample from the patient for the quantity of MRP8/14 in the sample and comparing it with the quantity of MRP8/14 present in standard samples correlated with an appendicitis severity scoring system. A histologically-based appendicitis severity scoring system is also provided. Immunoassays and kits for performing the appendicitis assays of this invention are also provided, as are standard samples and data correlating MRP8/14 quantities present in patient samples to histologically-based appendicitis severity grades. The methods and immunoassay devices and kits of this invention are useful for managing the treatment of patients presenting with appendicitis symptoms.