Diagnostic miss rate for colorectal cancer: an audit

Colorectal cancer (CRC) is a common cancer worldwide. While screening improves survival, avoiding delayed diagnosis in symptomatic patients is crucial. Computed tomographic colonography (CTC) or colonoscopy is recommended as first-line investigation and most societies recommend counseling patients undergoing colonoscopy about a miss rate of 5%. This audit evaluates "miss rate" of colorectal investigations, which have led to diagnostic delay in symptomatic cases in a district general hospital in the United Kingdom.

This is a retrospective review of 150 consecutive CRC cases presenting between August 2010 and July 2011. Evidence of bowel investigations done in the 3 years prior to diagnosis was obtained from computerized health records. Data regarding previous bowel investigations such as colonoscopy, CTC, double contrast barium enema (DCBE), and CT abdomen/pelvis were collected.

6.7% cases were identified via screening pathway while 93% were identified through symptomatic pathway. 17% (26/150) of newly diagnosed CRC had been investigated in the preceding 3 years. Of these, 8% (12/150) had false negative results. The false negative rate for CRC diagnosis was 3.5% for colonoscopy (3/85), 6.7% for CTC (1/17), 9.4% for CT (5/53), and 26.7% for DCBE (4/15). Some patients had a missed diagnosis despite more than one diagnostic test. Time delay to diagnosis ranged from 21-456 days.

17% of patients diagnosed with CRC had been investigated in the previous 3 years. Higher miss rate of barium enema should preclude its use as a first-line modality to investigate CRC.