ED ultrasound helpful but not definitive in diagnosing gallstones

ED ultrasound helpful but not definitive in diagnosing gallstones

Last Updated: 2011-04-08 10:10:28 -0400 (Reuters Health)

By Karla Gale

NEW YORK (Reuters Health) - Ultrasonography by emergency physicians can help to detect or rule out gallstones, say the authors of a systematic review and meta-analysis.

A positive ultrasound (US) exam in the emergency department (ED) can't "in itself make the diagnosis of cholelithiasis," they say in their report. And negative results don't rule it out if the pretest probability is high.

But if clinical suspicion for biliary colic is low and gallstones don't show up on US, then alternative diagnoses should be considered, according to Dr. Marshall Ross at the University of Calgary in Alberta, Canada, and colleagues.

Emergency room doctors often do US exams to look for abdominal aortic aneurysms or pericardial effusions, and "strong evidence" shows they're quite accurate at it, the authors note in the March issue of Academic Emergency Medicine.

But how well emergency physicians do with US for gallstones has not been clear, the authors say. In particular, research has shown that false negatives in the ED are most often due to stones that are less than 4 mm in diameter or impacted in the gallbladder neck.

To assess the diagnostic accuracy of emergency department US, the research team searched MEDLINE, EMBASE, the Cochrane library, and other sources for original research on prospectively collected data.

They required that studies have an acceptable reference standard (e.g., imaging studies interpreted by radiologists, or surgical findings).

After reviewing 917 articles with relevant titles, they identified eight studies for their final analysis, involving 710 patients altogether. In each study, the emergency physicians who performed and interpreted the US exams were unaware of what radiologists diagnosed.

The number of patients per study ranged from 35 to 127, and the prevalence of gallstones ranged from 46% to 80% (median 60%).

The pooled estimates for sensitivity and specificity were 89.8% and 88.0%, respectively. The estimated positive likelihood ratio was 7.5 and the negative likelihood ratio was 0.12.

Operators had a wide range of experience, and some were "admittedly na�ve," the investigators point out.

But a summary receiver operator curve, constructed with a regression model based on unweighted least squares estimation, showed "no implicit variation in sensitivity and specificity across studies due to operator-dependent differences in what defined a positive or negative test result," they say.

Dr. Ross and his colleagues suggest that emergency physicians can make a provisional diagnosis of acute symptomatic cholelithiasis when their US exams show gallstones in association with right upper quadrant pain, epigastric pain, or flank pain. If symptoms resolve, appropriate follow-up after discharge should be arranged, they say.

The research team notes that the small size and number of studies prevented any meaningful subgroup analysis (including results based on operator experience). Those factors also prevented any determination of whether ED physicians could accurately detect secondary signs of cholecystitis - such as pericholecystic fluid, a thickened gallbladder wall, or a sonographic "Murphy's sign" (i.e., point tenderness beneath the probe upon pressure above the gallbladder).

The authors warn of a potential for selection bias, since all eight studies used convenience sampling. They also say none of the studies adequately described scanning techniques.

SOURCE: http://bit.ly/h8hA7I

Acad Emerg Med 2011;18:227-235.