Patients who have a positive FOBT after a recent negative colonoscopy can be reassured they are unlikely to have colorectal cancer, an Australian study suggests.

Gastroenterologists at Liverpool Hospital in NSW found that a previous negative colonoscopy done within four years conferred a 100% negative predictive value for detection of new colorectal cancer despite a recent positive FOBT.

In findings presented at Digestive Diseases Week 2019 in San Diego, the researchers report results from a study of 740 patients (median age 64 years old) who had colonoscopies performed at the hospital between 2015 and 2018.

Overall 27 (3.6%) of the patients had colorectal cancer, 362 (48.9%) had at least one adenoma and 188 (25.4%) had an advanced adenoma (size>10mm, high-grade dysplasia or villous architecture).

In the cohort of 740 patients there were 219 (29.6%) who had a previous colonoscopy, of which about half (111) were negative. Among patients who had a negative colonoscopy within the previous four years, none had colorectal cancer and seven had an advanced adenoma.

In contrast, colorectal cancers were found in 22 (4.9%) of the 452 patients with no prior colonoscopy, and 129 patients (28.5%) had an advanced adenoma.

The study investigators, led by Dr Nivedita Rattan, identified male gender, age and no previous colonoscopy as significant independent predictors for the detection of advanced adenomas or colorectal cancer.

A personal history of polyps, family history of colorectal cancer, current abnormal symptoms and quality of bowel preparation of the previous colonoscopy were not significant predictors.

Therefore any prior colonoscopy carried a better prognosis for detection of advanced pathology in a patient with current positive FOBT, they concluded.

“These findings could potentially provide guidelines to managing patients with positive FOBT but previous negative colonoscopy,” they said.