Diagnostic Studies

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Results of laboratory studies in patients with biliary colic are frequently normal. The hemogram may reveal chronic anemia with or without evidence of hemolysis in patients with pigment stones. The white blood cell count, serum bilirubin level, alkaline phosphatase level, and aminotransferase levels are often normal. The serum lipase level should be obtained to rule out pancreatitis. The urine must be examined to exclude other causes of abdominal pain. In females, serum or urine pregnancy testing should be performed to rule out obstetric causes of abdominal pain. A negative pregnancy test result also enables one to proceed safely with radiologic studies, if indicated.

The presence of leukocytosis or abnormal liver function study results or lipase levels are often used as indicators for the diagnosis of acute cholecystitis. However, no single test or combination of laboratory tests has a sufficiently high sensitivity to detect acute cholecystitis. 12 A retrospective review of emergency department patients with acute cholecystitis found that 32 percent lacked a white blood cell count greater than 11,000 cells/mL. 13 Typical signs, symptoms, and laboratory findings may not be present in patients over age 60. The sensitivity of Murphy's sign is only 48 percent in the elderly. 14 In a cohort of geriatric emergency department patients with abdominal pain who were determined at surgery to have acute cholecystitis, 56 percent were afebrile, 41 percent had no leukocytosis, and 13 percent were both afebrile and had normal values on routine laboratory tests.15

Additional studies in patients with biliary colic may be performed to support the diagnosis and rule out other causes of upper abdominal pain with nausea. Plain film radiographs of the abdomen demonstrate gallstones in only 10 to 20 percent of cases. The majority of stones are cholesterol and therefore radiolucent. Pigment and mixed stones containing at least 4 percent calcium by weight are radiopaque. Abdominal films are more useful in excluding other causes of pain. A chest radiograph should be obtained to identify right lower lobe pneumonia or pleural effusions. A 12-lead electrocardiogram should be obtained in all older patients to exclude myocardial ischemia or infarction.

Ultrasonography is now the initial diagnostic modality of choice. It may show the presence of stones as small as 2 mm, gallbladder distention, wall thickening, and pericholecystic fluid, and during the procedure a sonographic Murphy sign may be elicited. Ultrasonography has a sensitivity of 94 percent and a specificity of 78 percent for the diagnosis of acute cholecystitis.16

Computed tomography (CT) scanning can be most useful in the diagnosis of acute cholecystitis when other intraabdominal disorders are considerations in the differential diagnosis. Wall thickening, pericholecystic fluid, and subserosal edema can be identified. However, the sensitivity of CT scanning is insufficient (as low as 50 percent) for it to replace ultrasonography as the diagnostic procedure of choice. 17

Radioisotope cholescintigraphy using technetium-iminoacetic acid analogues (HIDA), has a sensitivity and specificity of 97 percent and 90 percent, respectively. 16 The study is performed by injecting radioisotopes intravenously. The material is absorbed by the hepatocytes and secreted into the biliary tract. A normal patient will have a clearly outlined gallbladder and cystic duct within 1 h. Failure to demonstrate the gallbladder within this time frame is consistent with cystic duct obstruction. The HIDA scan can only be used in patients with a serum bilirubin level of less than 5 mg/dL. With serum bilirubin above this level, an alternative radioisotope study, the DISIDA scan, is preferred.

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