Study objectives: Bedside ultrasonography has proven to be a useful adjunct in the diagnoses of abscesses. To date, there are no studies evaluating the utility of ultrasonography in diagnosing superficial abscesses by midlevel providers (physician assistants and nurse practitioners). We determine the ability of midlevel providers to identify superficial abscesses using bedside ultrasonography assessment.

Methods: This is an institutional review board–approved, prospective, observational study of adult patients (>18 years) presenting to the emergency department (ED) with a suspected superficial abscess according to physical examination findings of localized swelling, redness, warmth, or fluctuance. The study was conducted in an urban university hospital with a census of more than 130,000 per year during a 6-month period. Bedside ultrasonography was performed on the affected area by a midlevel provider working in the Fast Track area or by emergency medicine faculty or residents working in the main ED. All providers were given the same 1-on-1 15- to 30-minute instruction on the required ultrasonographic technique to determine the presence of an abscess by emergency medicine faculty trained in ultrasonographic techniques. A Terason 2000 laptop ultrasonograph was used. After the ultrasonographic examination, the same provider performed blind needle aspiration or incision and drainage as per the current standard of care. The presence of purulent fluid was considered the criterion standard for the presence of an abscess. A data collection tool was completed by the same provider. Information collected included the patient's demographic data, comorbidities, physical examination findings, ultrasonographic results, and the clinical presence of an abscess according to needle aspiration or incision and drainage findings. Radiology faculty reviewed all ultrasonographic images.

Results: Forty-one patients were enrolled, 16 women and 21 men. All providers were able to detect a fluid collection on ultrasonography when an abscess was clinically present (n=30, 11 emergency medicine residents and faculty, 19 midlevel providers). An abscess was correctly identified on ultrasonography by emergency medicine residents and faculty in 81% (9/11) of cases and by midlevel providers in 84% (16/19) of cases. The average diameter of the fluid collection detected by ultrasonography was 1.34 cm (SD 0.98, median 1.05). The sensitivity for abscess detection using ultrasonography by midlevel providers was 100% (the same as for emergency medicine faculty and residents), with a positive predictive value of 79.2% (compared with 92.3% for emergency medicine faculty and residents). However, the likelihood ratio for correctly identifying an abscess was 1 for midlevel providers and 2.99 (95% confidence interval 2.37 to 3.77) for emergency medicine faculty and residents.

Conclusion: Midlevel providers can correctly identify superficial abscess by ultrasonography; however, their limited experience and training may result in overinterpretation of findings.