POCUS for Appendicitis in Moderate to High Pre-test Probability

By Michael Prats, MD

Appendicitis byte

Clinical Ultrasound Is Safe and Highly Specific for Acute Appendicitis in Moderate to High Pre-test Probability Patients

Western Journal of Emergency Medicine May 2018 - Pubmed Link

Take Home Points

1. In this small study, there was high specificity for emergency physician performed ultrasound in acute appendicitis in patients with at least moderate pre-test probability.

2. Point of care ultrasound should probably not be used as a sole diagnostic to rule out appendicitis.


Appendicitis has had a tumultuous relationship with point of care ultrasound. Everyone wants it to be accurate so we can cut down on the CTs we perform and expedite management of these patients; however, the results of past studies have been mixed. Most recently, a metanalysis by Fields et al in 2017 analyzed patients of any age who received a point-of-care ultrasound for appendicits. Pooled data from 21 studies, amounting to 6,636 patients, showed overall 91% (83-96%) sensitivity and 97% (91-97) specificity. For emergency physicians alone, they found 80% sensitivity, 92% specificity. Lots of heterogeneity in these studies. In pediatrics, ultrasound is a first line study for appendicitis and may save time and avoid CT, but in adults, most are still relying on CT most of the time. What this study adds is offering the idea that if we risk stratify patients into a higher pre-test probability, maybe this would allow point of care ultrasound to be more accurate, even with a group of sonographers with variable levels of expertise.


Can emergency physicians diagnose appendicitis with high specificity using combination of risk assessment and point-of-care ultrasound (referred to as Clinical Ultrasound or CUS in this study)?


Adult and pediatric patients

Three urban academic emergency departments (two were adult centers, and one was pediatric center) from July 2014 to September 2016


  • Suspected acute appendicitis

  • Had emergency physician performed ultrasound (called CUS) - at the discretion of treating clinician


  • Had other imaging prior to CUS

  • Data collection had missing information


Prospective observational convenience sample

Prior to CUS, treating physician recorded pre-test probability on 10 pt visual analog scale (VAS), based on gestalt

After ultrasound, clinician determined - + appendicits, - appendicitis, or indeterminant and recorded it. Then noted confidence in ultrasound interpretation on 10 point VAS.

Pre-test probablity was categorized as:

  • Low (1-3 on scale)

  • Moderate (4-6)

  • High (7-10)

Criterion standard for diagnosis determined by surgical pathology, chart review at discharge and one week after ED visit (including statewide EMR review).

Who did the ultrasounds?

33 different sonographers

  • Emergency medicine residents

  • Ultrasound fellows

  • Emergency medicine faculty

All underwent 20 minute CUS training on appendicitis, including didactics and hands on scanning.

Stated that most operators had performed 100 prior examinations (unclear if this means exams for appendicitis, which would be high, or any focused ultrasound, which would be more expected).

The Scan

Linear transducer


Their protocol:

After analgesia, graded compression over maximal site of pain.

Positive study was:

  • Dilated >6mm diameter

  • Non-compressible

  • Blind-ending tubular structure

Learn POCUS for Appendcitis at 5 Minute Sono!


The Patients

105 patients analyzed

N = 76 had moderate or high pre-test probability (power calculation estimated sample size 75 needed)

  • Of these, 28 (36.8%) had acute appendicitis

  • 27 (35.5%) pediatric cases

  • 2 pregnant women

Primary Outcome

Accuracy of Emergency Physician Clinical Ultrasound for Appendicitis

Sensitivity 42.8% (CI 25-62.5%)

Specificity 97.9% (CI 87.5-99.8%)

+LR 20.6

-LR 0.58

Additional Findings

31 studies had high confidence in the study interpretation. Analyzing these studies alone:

  • Sensitivity 80%

  • Specificity 100%

16 false negatives → All interpreted as indeterminate → CT performed which showed appendicitis

1 false positive (low confidence in interpretation) → CT showed obstructing ureteral stone at right ureterovesicular junction

2 patients went to operating room based on positive CUS (were they pediatric patients? - we don’t know)

Sonographers had range of 1-13 scans each

  • 52.6% performed by residents

Faculty and fellows (total of 36 exams) had 100% specificity. Best sensitivity was 75% by fellows.

Interrater reliability (based on 20 randomly selected studies), comparing EP images to review by blinded fellowship trained expert, was 100%, Kappa = 1


Small convenience sample of patients. Did not distinguish pediatric from adult patients (also could be a strength of the study).

Could have missed some patients outside of the 1 week follow up that had appendicitis.

Although only a 20 minute training period is noted, based on having had at least 100 ultrasound experience, this was likely not an entirely novice population of physician sonographers.

Did not assess patient centered outcomes such as time to intervention, morbidity, radiation, or cost.


Secondary signs of appendicitis on ultrasound may actually be more accurate findings of acute appendicitis, and that was not assessed here. There is also disagreement regarding the diameter cut off point. However, even without some of these more difficult to discern findings, the specificity was high - so do we even need these? Secondary signs of appendicitis are likely more helpful when trying to rule it out.

This study supports an ultrasound first approach to suspected acute appendicitis, in both adults and children. If you have a reasonable pre-test probability, you have good confidence in your ultrasound, and you have a positive study - there is a good chance there is an appendicitis. On the other hand, based on this study and those prior to it, don’t try to rule out appendicitis with a point of care study.

What do we do when there is low pre-test probability, but we still need to rule it out? Should we get the ultrasound or not? This study does not address this questions. Based on prior results, a positive study in that case still has a good chance of being appendicitis. What to do from there is based on your general surgeon’s practice.

Take Home Points

1. In this small study, there was high specificity for emergency physician performed ultrasound in acute appendicitis in patients with at least moderate pre-test probability.

2. Point of care ultrasound should probably not be used as a sole diagnostic to rule out appendicitis.

Our score

3 Probes

Cite this post as

Michael Prats, MD. POCUS for Appendicitis in Moderate to High Pre-test Probability. Ultrasound G.E.L. Podcast Blog. Published on June 04, 2018. Accessed on April 14, 2021. Available at https://www.ultrasoundgel.org/48.
Published on 06/04/18 06:00 AM
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