Pearls of Wisdom: How Accurate Are Colonoscopies?
Concerned about his risk for colon cancer, Joseph, a 52-year-old man, consults with you about bright red blood around his rectum. Physical examination is negative except for external hemorrhoids and positive fecal occult blood test.
He recently underwent colonoscopy by an experienced colonoscopist, and no pathology was identified except for his external hemorrhoids. He is quite concerned about colon cancer and asks you: “What is the chance that they missed something?”
In a colonoscopy performed by experienced colonoscopists, what is the chance that they missed something?
A. Essentially Zero
B. <5%
C. ±25%
D. >35%
What is the correct answer?
(Answer and discussion on next page)
Louis Kuritzky, MD, has been involved in medical education since the 1970s. Drawing upon years of clinical experience, he has crafted each year for almost 3 decades a collection of items that are often underappreciated by clinicians, yet important for patients. His “Pearls of Wisdom” as we like to call them, have been shared with primary care physicians annually in an educational presentation entitled 5TIWIKLY (“5 Things I Wish I Knew Last Year”…. or the grammatically correct, “5 Things I Wish I’d Known Last Year”).
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Answer: ±25%
No test is perfect (100% sensitivity and specificity), and that includes colonoscopy.
The Research
In a 1997 trial, endoscopists from the Department of Gastroenterology at Indiana University performed colonoscopy on 183 individuals who consented to undergo the procedure twice on the same day.1
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Question: How Good Is Colonoscopy?1
Their indications for colonoscopy ranged from screening to GI bleeding and abdominal pain. To ensure that colonoscopy positioning did not affect outcomes, positioning was randomized.
A “missed lesion” was any polyp seen on the second examination that was not reported on the first. The gastroenterologists were all quite experienced: the least experienced colonoscopist had performed over 500 procedures.
The Results
Overall, there were 89 adenomas seen on examination #2 that were not seen on the first colonoscopy, for an overall miss rate of 24%.
Bottom Line (No Pun Intended)1
While at first glance this number may seem alarming, it is important to recall that it is only the adenomas of 10 mm size or greater that have substantial premalignant potential. For this size lesion, only 6% were missed, and no grossly malignant lesions were missed.
There is no perfect test, and although the accuracy of colonoscopy is excellent as a screening test, some potentially important lesions are missed.
Reference:
1. Rex DK, Cutler CS, Lemmel GT, et al. Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies. Gastroenterology 1997;112:24-28.