The invention relates to an in vitro method for the diagnosis of acute pancreatitis (AP) in a subject by detection of Glycoprotein 2 isoform alpha (GP2a) protein. In particular the invention pro-vides an in vitro method for the diagnosis of acute pancreatitis (AP) in a subject by detection of Glycoprotein 2 isoform alpha (GP2a) protein, comprising providing a sample of a human subject exhibiting symptoms of having pancreatic disease, wherein said sample is obtained from the subject within 72 hours of the appearance of said symptoms, providing an affinity reagent directed against GP2a, contacting said sample with said affinity reagent thereby capturing GP2a from said sample, and determining the concentration of GP2a from said sample, wherein determining a concentration of GP2a in said sample that is greater than the average concentration of GP2a in control samples, such as in a group of healthy individuals, indicates the presence of AP and the absence of one or more of chronic pancreatitis, pancreatic cancer, gastrointestinal cancer, liver cancer, neuroendocrine tumor, sarcoma, peptic ulcer or peritonitis. The invention further provides a kit and a system developed for carrying out the claimed method and determining the concentration of GP2a and performing an automated analysis of one or more samples.