Positive Predictive Value of Fecal Occult Blood Testing in Asymptomatic Average-Risk Patients with Varying Degrees of Chronic Kidney Disease

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Background: Although patients with chronic kidney disease (CKD) are at increased risk of bleeding due to intrinsic platelet dysfunction, abnormal platelet-endothelial interaction, uremia, and other defects, it is unknown whether the performance characteristics of fecal occult blood testing (FOBT) are affected. Since CKD may be associated with gastrointestinal bleeding from trivial mucosal lesions, we hypothesized that the positive predictive value (PPV) of FOBT for clinically important lesions would decrease as the stage of CKD worsens. Methods: Consecutive asymptomatic, average-risk patients ≥50 years of age who were referred for evaluation of a positive FOBT were prospectively identified. Prior to colonoscopy, all patients were interviewed by a research assistant who obtained detailed demographic and clinical data. Colonic lesions which were considered clinically important included cancer, adenomatous polyps ≥1 cm, active colitis, colonic ulcers ≥1 cm, and vascular ectasias that numbered 5 or more or were ≥8mm in diameter. Using the Modified Diet in Renal Disease (MDRD) equation, we estimated the glomerular filtration rate (GFR) in ml/min/1.73m2 and staged the severity of CKD using standard criteria as follows: normal/stage 1 (GFR ≥ 90), stage 2/3 (GFR 30 - 89), and stage 4/5 (GFR <30 or dialysis). Results: Among the 1,225 patients enrolled, the mean age was 68.4±9.6 years; 539 were white, 427 were black, 210 were Hispanic, and 49 were “other” racial groups. The stage of CKD was none/stage 1 in 531 patients, stage 2/3 in 497, and stage 4/5 in 197 subjects. Colonoscopy was complete to the cecum in 96.6% of patients and did not differ according to the stage of CKD (p = 0.18). Clinically important lesions were identified in 23.9% of patients with none/stage 1 CKD, 32.8% of those with stage 2/3 CKD, and 42.6% of subjects with stage 4/5 CKD (p < 0.001). Compared to patients with none/stage 1 CKD, the odds of identifying a clinically important lesion was 1.61 (95% CI, 1.21 - 2.15) in patients with stage 2/3 CKD and 2.33 (95% CI, 1.62 - 3.36) in subjects with stage 4/5 CKD after adjusting for age, sex, race, NSAID use, aspirin use, alcohol use, and smoking. The prevalence of adenomas ≥1 cm (15.1% vs 20.1% vs 22.8%, p = 0.007), cancers (5.1% vs 10.1% vs 13.2%, p < 0.001), and vascular ectasias (1.7% vs 2.4% vs 6.1%, p = 0.003) increased with the severity of CKD. Conclusions: Contrary to our initial hypothesis, we found that the PPV of FOBT for clinically important colonic lesions increases as the severity of CKD worsens. Complete colonoscopy should be offered to all individuals with a positive FOBT, regardless of the stage of CKD.