Management of Positive FOBT in Elderly Patient with Prior Normal Colonoscopy
Despite the normal colonoscopy one year ago, this elderly patient with a positive FOBT and anemia requires repeat colonoscopy now, as a positive FOBT always mandates colonoscopic evaluation regardless of prior negative studies. 1, 2
Rationale for Repeat Colonoscopy
A single positive FOBT requires immediate colonoscopy without repeating the test, as this is the definitive diagnostic procedure that allows direct visualization of the entire colon and the opportunity to identify and remove adenomatous polyps or detect colorectal cancer at an early stage. 1, 2
The one-year interval since the last colonoscopy does not preclude the development of new pathology, particularly in elderly patients who have higher rates of colorectal malignancy and vascular lesions. 3
Repeating the FOBT after a positive result is inappropriate and delays proper diagnostic evaluation. 1, 2
Timing Considerations
Colonoscopy should be performed within 60 days of the positive FOBT result to minimize the risk of disease progression. 1, 2
Delays beyond 180 days are associated with increased risk of colorectal cancer in a dose-response fashion, with each additional month of delay increasing both colorectal cancer incidence and mortality. 2
Bidirectional Endoscopy Approach
Given the concurrent anemia, bidirectional endoscopy (both upper endoscopy and colonoscopy) should be strongly considered, as dual pathology occurs in 10-15% of patients with iron deficiency anemia. 4
Upper endoscopy can reveal a cause in 30-50% of patients with iron deficiency anemia, with common findings including peptic ulcers, gastric cancer, and angiodysplasia. 4, 5
Small bowel biopsies should be taken during upper endoscopy as 2-3% of patients with iron deficiency anemia have coeliac disease, even in the absence of typical gastrointestinal symptoms. 4
The presence of upper GI lesions such as oesophagitis, erosions, or peptic ulcer should not deter lower GI investigation until colonoscopy is completed, as dual pathology is common. 4
Specific Considerations for Elderly Patients
In elderly patients, investigation of the colon is likely to be more productive than upper endoscopy alone, though both should ideally be performed. 4
Elderly patients are more likely to have vascular lesions (angiodysplasia) accounting for up to 40% of gastrointestinal bleeding causes. 3
Anti-platelet use and positive FOBT are associated with significant GI lesions, with odds ratios of 2.37 and 2.83 respectively. 5
Common Pitfalls to Avoid
Do not attribute the positive FOBT to the prior normal colonoscopy – interval cancers and new lesions can develop within one year. 1, 2
Do not use flexible sigmoidoscopy alone as follow-up – this is inadequate as it only visualizes the distal colon and may miss significant proximal lesions. 1, 2
Do not accept upper GI findings (such as gastritis or peptic ulcer) as the sole explanation without completing colonoscopy, unless gastric cancer or coeliac disease is found. 4
Lesions commonly missed during colonoscopy include angiectasias and neoplasias, emphasizing the need for high-quality examination. 3
Additional Evaluation
Coeliac serology (tissue transglutaminase antibody) should be checked if not previously done, as the probability of coeliac disease in iron deficiency anemia is approximately 5%. 4
Urine testing for blood is recommended, as approximately 1% of patients with iron deficiency anemia will have renal tract malignancy. 4
If bidirectional endoscopy is negative and anemia persists or is transfusion-dependent, further small bowel evaluation with capsule endoscopy or enteroscopy may be warranted. 4