FAST Exam in Blunt Abdominal Trauma

Andrew Matella DO 

Hypothetical Scenario:

1 year old male presents to the ED after being struck in the abdomen with a baseball bat several times just prior to arrival. Patient complaining of right sided abdominal pain. 

Vitals: HR 110 BP 145/89 RR 24 Spo2 99% on RA Temp 98.6

Whats the plan?

Morphine for pain, basic labs, slap a lidocaine patch on there

Norco prescription with incentive spirometer and send home

Repeat Exam

Patient complains of worsening pain! 

Repeat vitals

HR 122 BP 115/75 RR 25 Spo2 98% on RA Temp 98

Did we miss a diagnosis?

Let's look at the FAST scan criteria!

How do we stratify risk within in our patient's with the FAST Scan? 

The Unstable Patient

In hemodynamically unstable patients (SBP <90 mm Hg) with blunt abdominal trauma, bedside ultrasound, when available, should be initial diagnostic modality performed to identify the need for emergent laparotomy (B level recommendations per ACEP)

If Positive: 



Multiple large studies have found that the specificity of a positive FAST exam in an unstable patient approaches 100% [1,4,6]

If negative: 

Keep looking for signs of shock

Resuscitate and reevaluate with FAST Exam or CT if stable enough

Sensitivity varies (anywhere from 79-100% [1,4])

In order to cause hypotension from intraperitoneal bleed, you need to lose close to ~2L of blood and usually only require 150-200cc of blood in abdomen to be seen on FAST

The Stable Patient

If positive, current recommendations from ACEP/UTD/EMRAP/Tintinelli’s is to obtain a CT scan to further evaluate the specific location and severity of injury

If negative ,FAST in HDS patient DOES NOT rule out intra-abdominal injury

FAST + has about 99% specificity based off of several large studies146, sensitivity varied. Retrospective cohort study with 421 patients demonstrated sensitivity of 67% in this group [3].

Large prospective study of 2100 patients demonstrated sensitivity of 41%6.

Patient has a negative FAST, but you're still suspicious of injury. Let's take a look at some other signs: 

HDS patient with negative FAST but increased likelihood of intraabdominal injury [5]:

-The presence of a seat belt sign (LR+ 5.6-9.9).

-Abdominal rebound tenderness (LR+ 6.5, 95% CI: 1.8-24).

-Abdominal distension (LR+ 3.8, 95% CI: 1.9-7.6).

-Abdominal guarding (LR+ 3.7, 95% CI: 2.3-5.9).

-Concomitant femur fracture (LR+ 5.2, 95% CI: 2.1-4.1).

-Abdominal tenderness on exam or ecchymosis

-Pelvic or lower rib fractures


-Costal margin tenderness

-Hematocrit less than 30%

-Hematuria (>25 RBCs/hpf)

-Elevated LFTs

-Mechanism of injury

In the end...

Gold Standard: CT Scan

If the CT is negative: 

Level B Recommendations

Level C Recommendations

Limitations of Ultrasound: 

Need at least 150-200cc of fluid in order to detect on US

Unable to differentiate blood from ascitic fluid, urine and peritoneal dialysate 

Inability to determine exact source of the bleed

US unable to visualize retroperitoneal structures and solid organ subcapsular injuries

Can miss hollow viscus injuries

Image quality can be limited due to body habitus or bowel gas

Take Away Points: 

1) In the unstable patient, the US is the gold standard in blunt abdominal trauma. If positive, they should be going to the OR. 

2) Specificity of the FAST exam near 100%.

3) You cannot reliably exclude intraabdominal injury in the HDS patient with negative FAST. A negative FAST on these patient’s basically means nothing.

4) Just like everything in medicine, clinical gestalt/physical exam extremely important in next steps for the HDS patient with a negative FAST. 


1. Bloom BA, Gibbons RC. Focused Assessment with Sonography for Trauma. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:

2. Clark, Samuel, Dierks, Debra. Initial evaluation and management of blunt abdominal trauma in adults.

3. Dammers, D., El Moumni, M., Hoogland, I. et al. Should we perform a FAST exam in haemodynamically stable patients presenting after blunt abdominal injury: a retrospective cohort study. Scand J Trauma Resusc Emerg Med 25, 1 (2017).

4. Jansen JO, Yule SR, Loudon MA. Investigation of blunt abdominal trauma. BMJ. 2008 Apr 26;336(7650):938-42. doi: 10.1136/bmj.39534.686192.80. PMID: 18436949; PMCID: PMC2335258.

5. McVaney Kevin, Haamid Ameera. Blunt Abdominal Trauma. In: Mattu A and Swadron S, ed. CorePendium. Burbank, CA: CorePendium, LLC. Updated January 28, 2021. Accessed October 24, 2022.

6. Natarajan B, Gupta PK, Cemaj S, Sorensen M, Hatzoudis GI, Forse RA. FAST scan: is it worth doing in hemodynamically stable blunt trauma patients? Surgery. 2010 Oct;148(4):695-700; discussion 700-1. doi: 10.1016/j.surg.2010.07.032. Epub 2010 Aug 30. PMID: 20800865.

7. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 8e Tintinalli JE, Stapczynski J, Ma O, Yealy DM, Meckler GD, Cline DM. Tintinalli J.E., & Stapczynski J, & Ma O, & Yealy D.M., & Meckler G.D., & Cline D.M.(Eds.),Eds. Judith E. Tintinalli, et al.