Practical guidelines for the diagnosis of acute pancreatitis are presented so that a rapid and adequate diagnosis can be made. When acute pancreatitis is suspected in patients with acute onset of abdominal pain and tenderness mainly in the upper abdomen, the diagnosis of acute pancreatitis is made on the basis of elevated levels of pancreatic enzymes in the blood and/or urine. Furthermore, other acute abdominal diseases are ruled out if local findings associated with pancreatitis are confirmed by diagnostic imaging. According to the diagnostic criteria established in Japan, patients who present with two of the following three manifestations are diagnosed as having acute pancreatitis: characteristic upper abdominal pain, elevated levels of pancreatic enzymes, and findings of ultrasonography (US), CT or MRI suggesting acute pancreatitis. Detection of elevated levels of blood pancreatic enzymes is crucial in the diagnosis of acute pancreatitis. Measurement of blood lipase is recommended, because it is reported to be superior to all other pancreatic enzymes in terms of sensitivity and specificity. For measurements of the blood amylase level widely used in Japan, it should be cautioned that, because of its low specificity, abnormal high values are also often obtained in diseases other than pancreatitis. The cut-off level of blood pancreatic enzymes for the diagnosis of acute pancreatitis is not able to be set because of lack of sufficient evidence and consensus to date. CT study is the most appropriate procedure to confirm image findings of acute pancreatitis. Elucidation of the etiology of acute pancreatitis should be continued after a diagnosis of acute pancreatitis. In the process of the etiologic elucidation of acute pancreatitis, judgment whether it is gallstone-induced or not is most urgent and crucial for deciding treatment policy including the assessment of whether endoscopic papillary treatment should be conducted or not. The diagnosis of gallstone-induced acute pancreatitis can be made by combining detection of elevated levels of bilirubin, transamylase (ALT, AST) and ALP detected by hematological examination and the visualization of gallstones by US.
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