Risk Factors Of False-Positive Fecal Immunochemical Test Results

BackgroundsColorectal cancer is at a high incidence in China.Fecal immunochemical test(FIT)can directly measure the concentration of hemoglobin in stool samples,and the sensitivity and specificity in the diagnosis of colorectal cancer were at a high level.At present,FIT has become the main method of colorectal cancer screening among population.Meta-analysis showed that,for the detection of advanced adenomas,the positive predictive values of FIT ranged from 28.6%to 62.9%,indicating that a large proportion of positive FIT results were false positive.A portion of the research focused on exploring the epidemiological risk factors associated with falsepositive FIT results.However,only a few studies have studied the relationship between falsepositive FIT results and upper gastrointestinal diseases.Whether people with false-positive FIT results are at higher risk of upper gastrointestinal diseases remains controversial.AimsThis study aimed to evaluate the risk factors associated with false-positive FIT results for the detection of lower gastrointestinal bleeding,and to explore the association of false-positive FIT results with other digestive diseases.MethodsPatients aged 50 to 75 years who underwent both gastroscopy and colonoscopy in Qilu hospital of shandong university were continuously and prospectively enrolled from April 2020 to April 2021.All patients were required to complete FIT test prior to colonoscopy.Falsepositive FIT refers to positive FIT without significant lower gastrointestinal lesions in subsequent colonoscopy.Logistic regression was applied to analyze the risk factors associated with false-positive FIT results.ResultsA total of 929 participants were prospectively enrolled.A total of 55 participants were diagnosed with advanced adenomas and 10 with colorectal cancers during colonoscopy.The positive rate of FIT was 16.04%(149/929).A total of 42 cases of colorectal cancer or advanced adenoma were detected in 149 positive FIT participants.Gastric cancer was detected more frequently in participants with positive FIT results(2.7%VS 0.4%,P=0.014).The sensitivity and specificity of FIT for the detection of colorectal cancer were 100.0%(95%CI:65.6%100.0%)and 84.9%(95%CI:82.4%-87.1%).For the detection of advanced adenoma,the corresponding values were 58.2%(95%CI:44.1%-71.1%)and 86.6%(95%CI:84.1%-88.8%).After correcting confounding factors,except colorectal cancer and advanced adenoma,male(OR=1.70,95%CI:1.14-2.55,P=0.010),colorectal inflammation(OR=2.62,95%CI:1.20-5.33,P=0.010),presence of ≥3 non-advanced adenomas(OR=1.68,95%CI:1.06-2.63,P=0.026)and gastric cancer(OR=10.96,95%CI:2.32-57.63,P=0.002)were also independent risk factors associated with positive FIT results after adjusting confounding factors.Moreover,after excluding all lower gastrointestinal lesions which may result in gastrointestinal bleeding,gastric cancer(OR=9.48,95%CI:2.04-49.19,P=0.004)was independent risk factor for false-positive FIT after adjusting confounding factors,while there was no significant correlation between false-positive FIT results and comsumption amount of meat,recent usage of aspirin,reflux esophagitis and peptic ulcer.Conclusion1.In addition to colorectal cancer and advanced adenoma,male,colorectal inflammation,presence of ≥3 non-advanced adenomas and gastric cancer were independent risk factors associated with positive FIT results.2.After excluding all lower gastrointestinal lesions which may result in gastrointestinal bleeding,gastric cancer was independent risk factor for false-positive FIT results.3.For patients with both positive FIT results and negative colonoscopy,other gastrointestinal diseases that may lead to false-positive results such as gastric cancer should be considered for examination closely.