In another study, 21,805 asymptomatic patients received iFOBT based on one stool sample collected by patients following the kit instructions on the day of or the day before the colonoscopy. Stool samples were analyzed using the Magstream 1,000/Hem SP automated system (from Fujirebio Incorporated, Tokyo, Japan), which is based on the HemeSelect system (from Beckman Coulter, Palo Alto, California). Sensitivity and specificity based on subsequent colonoscopy were, respectively, 65.8% and 94.6% for cancer and 27.1% and 95.1% for advanced neoplasm.
Fecal immunochemical tests may vary with regard to numbers of stools tested and cut-off values for a positive result.[30,31,32]
A systematic review to evaluate the comparative diagnostic performance of gFOBT and iFOBT in the context of a decision to introduce screening for CRC in the United Kingdom, included 33 studies evaluating gFOBT and 35 studies evaluating iFOBT, including nine that evaluated both gFOBT and iFOBT. There was no clear evidence for superiority of either gFOBT or iFOBT. Sensitivities for the detection of all neoplasms ranged from 6.2% (specificity 98%) to 83.3% (specificity 98.4%) for gFOBTs and 5.4% (specificity 98.5%) to 62.6% (specificity 94.3%) for iFOBT. Increasing sensitivity entailed adjusting cut-points to decrease specificity. Sensitivities were higher for the detection of CRC and lower for adenomas.
Some studies have utilized the quantitative ability of iFOBT to consider detection and specificity at various test cut-points for defining a positive test. One study  found that reducing the cut-point from the standard 100 ng/mL to 50 ng/mL increased the detection of advanced adenomas but had little impact on the detection of cancer. The number of colonoscopies required to detect a single advanced adenoma or cancer increased from 1.9 to 2.3; a 20% increase. Specificity declined from 97.8% to 96%.
Potential false-positive test results due to an increased risk of upper GI bleeding are of concern with FOBT testing and pretest protocols, therefore; low-dose aspirin regimens should be discontinued for a week or more prior to FOBT. The performance of iFOBT was tested in an ongoing diagnostic study (2005-2009) at 20 internal medicine GI practices in southern Germany. Nineteen hundred seventy-nine patients (233 regular low-dose aspirin users and 1,746 never users) were identified in the records for inclusion in the analysis. All patients provided one stool sample taken within a week before colonoscopy preparation, which was collected according to instructions in a container that was kept refrigerated or frozen until rendered to the clinic on the day of colonoscopy, and the patients agreed to complete a standard questionnaire regarding the use of analgesics and low-dose aspirin (for prevention of cardiovascular disease). Stool samples were thawed within a median of 4 days after arrival at the central laboratory (shipped frozen from the recipient clinics). Fecal occult blood levels were measured by two automated iFOBT tests according to the manufacturer's instructions (RIDASCREEN Haemoglobin and RIDASCREEN Haemo-/Haptoglobin Complex, r-biopharm, Bensheim, Germany) following clinical procedures and blinded to colonoscopy results. Advanced neoplasms were found in 24 aspirin users (10.3%) and in 181 nonusers (10.4%). At the cut-point recommended by the manufacturer, sensitivities for the two tests were 70.8% (95% CI, 48.9%-87.4%) for users compared with 35.9% (95% CI, 28.9%-43.4%) for nonusers and 58.3% (95% CI, 36.6%-77.9%) for users compared with 32% (95% CI, 25.3%-39.4%) for nonusers (P = .001 and P = .01, respectively). Specificities were 85.7% (95% CI, 80.2-90.1%) for users compared with 89.2% (95% CI, 87.6%-90.7%) for nonusers and 85.7% (95% CI, 80.2%-90.1%) for users compared with 91.1% (95% CI, 89.5%-92.4%) for nonusers (P = .13 and P = .01, respectively). For these iFOBTs, sensitivity for advanced neoplasms was notably higher with the use of low-dose aspirin while specificity was only slightly reduced, suggesting that there might be an advantage to aspirin use to increase sensitivity without much decrease in specificity.