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The diagnosis of AP is based on the presence of a chief complaint of epigastric abdominal pain in an appropriate individual who has a propensity for an etiology of AP and the finding of a laboratory test greater than threefold the upper limit of normal. Early imaging on admission or in the emergency room using CT is only indicated if diagnostic criteria are not fulfilled or there are findings that call the diagnosis of AP into question. Unfortunately, upper abdominal pain and tenderness is a frequent presentation of a plethora of disease states. Abdominal tenderness from AP may, in addition to epigastric location, also be present in the right upper quadrant. Findings of an acute abdomen may be present and, if so, CT imaging should be considered. The pain may radiate into the back and be associated with nausea and vomiting as well as fever [47]. The second consideration should be whether the patient has a potential etiology for AP (e.g. biliary disease, alcohol, trauma; see Table 1.1). Its presence increases our diagnostic certainty.

The laboratory diagnosis for AP has changed from determination of amylase to determination of lipase but the criterion is still a threefold increase. Lipase has several advantages over serum amylase: sensitivity is higher (82–100% vs. 67–100% for total amylase) and a slightly better specificity (82–100% vs. 85–98% for amylase) [47]. In addition, lipase offers a larger diagnostic window than amylase as it remains elevated for a longer period: amylase elevation lasts for only three to five days [48] whereas lipase shows persistent elevation for up to two weeks. Other causes of elevated lipase in patients with abdominal pain include trauma, appendicitis, diabetic ketoacidosis, small bowel disease, inflammatory bowel disease, ischemia, obstruction, cirrhosis, renal failure, and upper gastrointestinal malignancies (esophagus, stomach). It is questionable whether HTG may produce falsely low lipase levels [27]. There is no advantage of ordering amylase together with lipase. Unfortunately, laboratory tests are not diagnostic of AP and levels do not predict severity of AP. There is no benefit in monitoring laboratory diagnostic tests (i.e. amylase/lipase) during the course of AP [48].