The sensitivity and specificity of guaiac and immunochemical fecal occult blood tests for the detection of advanced colonic adenomas and cancer.

PURPOSE: Fecal immunochemical tests (FITs) have been developed to address analytical problems inherent in the older guaiac-based fecal occult blood tests (g-FOBTs). Our aim was to compare the performance characteristics of one g-FOBT (Hemoccult II) and two FITs (the Hemoccult ICT and MagStream HemSp) relative to colonoscopy for the detection of colorectal cancer and significant precursor lesions. We also examined whether a 1-day collection strategy would negatively impact test diagnostic performance. METHODS: We used a prospective observational cohort design in a Canadian population eligible for screening. All participants received colonoscopy after performing the occult blood tests. RESULTS: One thousand seventy-five individuals were enrolled (mean age 56.3 years, 53.8 % females). Using colonoscopy as the gold standard, the sensitivity for screen-relevant neoplasm was determined for Hemoccult II (7.2, 95 % CI: 1.1-13.4), Hemoccult ICT (23.2 %: 13.2-33.1), and MagStream HemSp using 67 µg/gram stool as the cut-off (23.2 %: 13.2-33.1). The Magstream HemSp, using a cut-off threshold of 30 µg/gram stool, had the lowest specificity at 87.6 % (85.4-89.6), while the Hemoccult II had the highest at 98.8 % (98.1-99.5). Single-day stool testing reduced the false-positive rates of all tests without significantly reducing the sensitivity. CONCLUSION: We found that FITs have a significantly increased sensitivity but reduced specificity for screen-relevant neoplasm compared to g-FOBT using colonoscopy as the gold standard. Optimal threshold levels for hemoglobin detection depend on the desired trade off between sensitivity and false-positive rate. Single-day testing with an FIT may be an option to enhance population compliance with screening.

Do cardiac troponins provide prognostic insight in hemodialysis patients?

BACKGROUND: The diagnosis of myocardial necrosis in patients with chronic renal failure is often difficult because biochemical markers of cardiac damage such as creatine kinase MB (CKMB) and cardiac troponin T (cTnT) may be spuriously elevated. Recent small studies also report unexplained elevations in cardiac troponin I (cTnI) in chronic renal failure patients undergoing hemodialysis. The relative incidence of elevated cardiac troponins in this population and their relationship to clinical events remain unknown. OBJECTIVE: To determine the incidence and prognostic significance of asymptomatic elevations of cTnT and cTnI in patients undergoing hemodialysis for chronic renal failure. DESIGN: Prospective cohort study. SETTING: University tertiary care teaching hospital. PATIENTS: One hundred thirteen patients over 21 years of age undergoing onsite hemodialysis were enrolled between December 1997 and February 1998. MEASUREMENTS: All-cause and cardiovascular mortality, hospitalization for acute myocardial infarction, unstable angina or congestive heart failure, new onset sustained arrhythmia or need for unscheduled emergency hemodialysis due to volume overload at 30 days and six months. RESULTS: The incidence of abnormal results for cTnT, cTnI and CKMB were 42%, 15% and 4%, respectively. Independent predictors of mortality at six months were median age greater than 63 years (odds ratio 14.3, 95% CI 1.5 to 130.3, P=0.019) and positive cTnT (odds ratio 13.6, 95% CI 2.5 to 73.2, P=0.002). Diabetics were more likely to have positive cTnI and cTnT results than nondiabetics (P<0.001 and P=0.023, respectively). CONCLUSIONS: cTnT is commonly elevated in patients with chronic renal failure even in the absence of acute coronary syndromes. cTnT may be an important independent prognostic marker in patients on hemodialysis for chronic renal failure. While less common, elevations of cTnI are more frequent than CKMB elevations. The basis of these cardiac troponin elevations is unclear. These findings may represent, in part, a subclinical myocardial injury, an inflammatory response to chronic renal failure or a chronically volume overloaded state.