This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows: To determine the diagnostic accuracy of biomarkers for detecting acute appendicitis in hospitalised adults with suspected acute appendicitis. SECONDARY OBJECTIVES: To determine (if possible) the diagnostic accuracy of biomarkers for detecting: uncomplicated and complicated (gangrenous or perforated) acute appendicitis; acute appendicitis in males and females; acute appendicitis in women of reproductive age; acute appendicitis in pregnancy; acute appendicitis at different time intervals from onset of pain.