POCUS for Abscess – How Accurate Is It?

December 4, 2019

Written by Clay Smith

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Point of care ultrasound (POCUS) was accurate for diagnosis of skin abscess, but the results of this review may have been inflated. It is likely most helpful in uncertain cases.

Why does the matter?
It is often difficult to distinguish cellulitis from abscess on clinical exam. How accurate is ultrasound in helping us distinguish the two?

Is it really that good?
This was a summary of a published systematic review of the diagnostic accuracy of POCUS for skin abscess. They found 8 studies with 747 patients, both children and adults. The sensitivity was 95.5% (95%CI 88.9 to 98.3) and specificity was 80.3% (95%CI = 56.4 to 92.7). There are several caveats. The gold standard for abscess differed from study to study. Most were convenience samples with cross contamination between clinicians and sonographers in medical decision making. All of this may have made the diagnostic accuracy look better than it actually was. Recent studies have show that POCUS is helpful in equivocal cases and unhelpful in cases in which the clinician was certain of the diagnosis prior to scanning. Overall, the authors ranked this yellow, which means POCUS has unclear benefit. They thought it was best in uncertain cases.

Source
Accuracy of Point-of-Care Ultrasound for Diagnosing Soft Tissue Abscess. Acad Emerg Med. 2019 Nov 1. doi: 10.1111/acem.13881. [Epub ahead of print]

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