Fecal Occult Blood Testing…Just Stop. Please.
Question. What’s the utility of Fecal Occult Blood Testing in the ED?
Bottom Line: FOBT/FIT does not have much value in the emergency department for the evaluation of GI bleeding (especially upper GI bleeding) in the emergency department.
FOBT
Approved for colorectal cancer screening (looking for occult LOWER GI bleeding)
Mechanism: Detects peroxidase activity of the heme portion of hemoglobin.
Can in theory pick up bleeding from anywhere in the GI tract (heme survives digestion).
Notoriously nonspecific. False positives from diet (red meat, some veggies), meds (NSAIDs), hemorrhoids.
Performance (cancer screening setting):
Sensitivity for colorectal cancer: ~30–40%
Specificity: ~90–95%
Very poor sensitivity for intermittent/low-volume bleeding (<20-50% for acute GI bleeding).
FIT
Mechanism: Uses antibodies to detect the globin portion of human hemoglobin.
More specific for human lower-GI bleeding (detects globin)
Globin is digested in the upper GI tract → FIT not particularly helpful in the upper GI bleed
Performance (screening setting):
Sensitivity for colorectal cancer: ~70–80%
Sensitivity for advanced adenomas: ~25–40%
Specificity: ~90–95%
Sensitivity for upper GI bleeding: cited in some studies as less than 20%
Misleading if used — negative test doesn’t exclude upper bleed, positive test doesn’t rule out lower mimics.
With either of these tests—the results should not change your management. If the patient says "I pooped black". Or "there was blood in my stool", just believe them, especially given the shitty (pun-intended) sensitivity and specificity of these tests.
You are going to utilize the history, physical exam, vital signs, and laboratory work-up (most importantly an acute Hb drop, maybe BUN/Cr elevation) to determine appropriate management and use validated risk scores (ie: GBS) to determine disposition. The American College of Gastroenterology focuses on risk stratification (such as GBS) to determine disposition and in fact makes no mention at all about fecal occult blood testing.
If the patient is stable and low risk, they get discharged with GI follow-up
You aren't going to change your disposition whether or not the FOBT testing is positive or negative.
If the patient is unstable and/or high risk, they get admitted with a GI consult.
You aren't going to change your disposition whether or not the FOBT testing is positive or negative.
GI shouldn't be making treatment decisions for acute GI bleeding on a FOBT/FIT—it's just not in their literature.
The definitive test for excluding or diagnosis upper and lower GI bleeding is upper endoscopy or colonoscopy. The urgency of said testing is dictated by the patient's clinical status.
Remember, if a test isn't going to change your management (whether it's a CBC or a FOBT), should you order it? And a test is not benign--it can lead to unnecessary further testing, false reassurances, and costs the hospital and the patient money. Many hospital systems have moved away from FIT/FOBT testing even being available in the ED setting to avoid unnecessary and generally unhelpful testing.
Resources
ACEPNow: https://www.acepnow.com/article/its-time-to-abandon-fecal-occult-blood-testing-in-the-emergency-department/
Qureshi, Ammar MD1; Ghobrial, Youssef MD2; De Castro, Joline MD2; Ajumobi, Adewale MD, MBA, FACG3. S1262 Fecal Occult Blood Testing Is Unnecessary in the Emergency Department. The American Journal of Gastroenterology 115():p S634, October 2020. | DOI: 10.14309/01.ajg.0000707096.39562.06
Cheers,
Dillon
