At a Glance
Acute pancreatitis is an inflammatory process of the pancreas with multiple etiologies (two of the most common are gallstone related and excessive alcohol abuse). A combination of the patient’s medical/social history combined with a clinical presentation of an acute onset of severe epigastria, nausea, and vomiting place acute pancreatitis high in the differential diagnosis. The diagnosis is then confirmed by radiologic studies and an elevation of pancreatic enzymes (lipase and amylase).
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Marked elevations of both amylase and lipase have been used to confirm the diagnosis of acute pancreatitis. Both can be elevated during cases of acute pancreatitis with lipase being more specific for pancreas than amylase.
Historically, lipase was not used as much as amylase, because lipase assay methods were not as consistent or standardized as amylase assays. At this point, lipase assays are more standardized and have risen to the forefront in the diagnosis of acute pancreatitis. However, amylase has not yet been discarded.
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Amylase
Elevations of amylase greater than three times the upper limit of normal is often given in the literature as diagnostic for acute pancreatitis. However, since amylase is not confined to the pancreas, sensitivity for diagnosis ranges from 45-85% with specificities ranging from 90-99%, depending on study reviewed.
Amylase levels rise within 6-24 hours and peak at approximately 48 hours. They then normalize over the next 5-7 days.
Lipase
Conversely, lipase is much more organ specific than amylase, such that acute elevations are characteristic of pancreatic disease. Test characteristics for lipase have sensitivities and specificities greater than 95% across multiple studies.
Lipase levels increase and peak earlier than amylase (4-8 hours and 24 hours, respectively) with a slow, gradual normalization during the following 8-14 days.
Of note, studies have noted that there is no increased diagnostic power by combining both amylase and lipase results.
What Factors, If Any, Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?
Hyperamylasemia not associated with acute pancreatitis:
Abdominal and thoracic malignancies
Biliary disease
Dissecting aortic aneurysm
Gastrointestinal viscous perforation
Head trauma with intracranial bleeding
Intestinal obstruction
Liver disease
Macroamylasemia
Mesenteric infarction
Myocardial infarction
Pancreatic pseudocyst
Pancreatic disease N.O.S.
Pulmonary embolism
Renal insufficiency
Ruptured ectopic pregnancy
Salivary gland disease
Hyperlipasemia not associated with acute pancreatitis:
Biliary disease
Diabetic ketoacidosis
HIV infection
Intestinal obstruction
Pancreatic carcinoma
Pancreatic disease N.O.S
Pancreatic pseudocyst
Renal failure
What Lab Results Are Absolutely Confirmatory?
Elevation of lipase greater than three times the upper limit of normal in the appropriate clinical setting is absolutely confirmatory.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
Several, common laboratory analyte values are also abnormal in cases of acute pancreatitis, but none are specific for the disease itself. These include white blood cell count (elevated), C-reactive protein (elevated), asparate aminotransferase (AST; elevated), alanine aminotransferase (ALT; elevated), and hematocrit (increased (in hemoconcentration) or decreased (hemorrhagic pancreatitis)).
Additional Issues of Clinical Importance
Elevated amylase without any other clinical, laboratory, or radiologic findings in the asymptomatic patient may be due to a condition known as macroamylasemia. In this situation, amylase is complexed to immunoglobulin G. This has no clinical significance. The diagnosis is made by measurement of urine amylase and creatinine levels and calculation of the amylase to creatinine ratio.
(amylase (urine) x Cr (serum)/ amylase (serum) x Cr (urine) x 100: a ratio less than 1 indicates macroamylasemia.
Essentially, macroamylasemia will not have elevated levels of urine amylase, whereas, hyperamylasemia (not macromylasemia) will have high levels of urine amylase.
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