Colorectal cancer is among the third most commonly diagnosed malignancy today. It is the second leading cause of cancer-related deaths across the world with an estimated 1.9 million new cases and about 9 lakh deaths in the year 2020 alone [1]. Early detection of colorectal cancers through specific screening can significantly reduce the rate of mortality by identifying precancerous lesions at early stages where there is curative treatment [2]. Among the methods of screening used colonoscopy and fecal immunochemical test (FIT) are the two most widely used approaches with unique advantages and limitations in terms of sensitivity, specificity, and invasiveness. Colonoscopy is considered the gold standard for CRC screening because it provides direct visualization of the entire colon and allows immediate biopsy or removal of suspicious lesions. It has been shown that the sensitivity of colonoscopy for detecting colorectal cancers and advanced adenomas was greater than 95% [3]. However, the procedure is invasive and can be associated with rare chances of bowel perforation and bleeding. Furthermore, the equipment is high cost and it also requires bowel preparation, sedation, and time for the procedure which can limit its acceptability in an asymptomatic population. Whereas the fecal immunochemical test (FIT) is a non-invasive and low-cost procedure. It appears to be an easily accessible screening modality that detects human hemoglobin stool, which is an indication of potential lower GI bleeding. FIT has slowly replaced the older guaiac-based fecal occult blood test (gFOBT). FIT appears to be superior in specificity and also does not require dietary restrictions [5]. Studies and trials have shown that FIT can be an effective population-level screening tool that can be performed annually. It also appears to be more acceptable to the general population. Having said that its sensitivity is generally lower than colonoscopy, particularly for detecting advanced adenomas and colorectal lesions on the right side [6]. Studies have reported sensitivity of FIT for colorectal ranges from 73% to 88% and specificity varies between 90% and 95%, depending on the threshold used and the study population included [7]. Since the global burden of CRC has been increasing in recent years due to changes in dietary habits and availability of fast foods and the logistical constraints of widespread use of colonoscopy screening understanding the comparative diagnostic accuracy of FIT in our cohort is essential. However, colonoscopy remains an indispensable tool for diagnostic follow-up, especially in high-risk individuals. FIT may offer an affordable and acceptable alternative for average-risk case screening. Research on FIT performance in identifying colorectal issues shows conflicting results depending on age characteristics, sex variations, and differences in location and hemoglobin cutoff levels used [8]. Based on this background we in the current study aimed to evaluate the sensitivity and specificity of the fecal immunochemical test (FIT) compared to colonoscopy as the reference standard for colorectal cancer screening. The results of this study can provide data to inform clinical decision-making optimize screening strategies and enhance compliance and outcomes in colorectal cancer prevention programs.

This prospective observational study was conducted in the Department of Gastroenterology, Government Medical College and Hospital, Sangareddy, Telangana. Institutional Ethical approval was obtained for the study based on Helsinki declaration of 1964 for human research with all its amendments till date. Written consent was obtained from all the participants of the study after explaining the nature of study in vernacular language. The sample was collected by convenience sampling method. Participants were recruited from individuals undergoing routine colorectal cancer screening or diagnostic evaluation.

Inclusion criteria

1. Age between 45 and 75 years
2. Average risk for colorectal cancer (no family history, personal history of colorectal neoplasia, or inflammatory bowel disease).
3. Ability and willingness to provide informed consent

Exclusion criteria

1. Known colorectal cancer or previous colorectal surgery
2. Overt gastrointestinal bleeding
3. Recent use (within 2 weeks) of non-steroidal anti-inflammatory drugs or anticoagulants
4. Incomplete colonoscopy or poor bowel preparation

Fecal Immunochemical Test (FIT): Participants (n=50) were instructed to collect a stool sample at home using a commercially available quantitative FIT kit which detects hemoglobin in stool using antibodies specific to human hemoglobin. Instructions were provided to avoid contamination and improper storage. Samples were returned for investigation within 24 hours and analyzed in the central laboratory. A hemoglobin concentration ≥20 µg Hb/g feces was considered a positive result, consistent with established diagnostic thresholds [9].

Colonoscopy Procedure: Colonoscopy examinations occurred within two weeks of performing FIT sampling for all participants. Experienced gastroenterologists who were unaware of the FIT outcomes conducted the colonoscopies. The procedure for bowel preparation utilized a standard polyethylene glycol solution. Gastroenterologists evaluated the entire colon segment extending from the cecum and collected biopsies or performed surgical removal of observed polyps and suspicious lesions which underwent histological analysis. Lesions were classified as no neoplasia, non-advanced adenomas (small, tubular adenomas without high-grade dysplasia), Advanced adenomas (≥10 mm, villous histology, or high-grade dysplasia), Colorectal cancer. The primary outcome measurements were the sensitivity and specificity of FIT for detecting colorectal cancer. Sensitivity and specificity for advanced adenomas as a secondary outcome. Colonoscopy with histopathology was used as the gold standard for comparison.

Statistical Analysis:

All the available data was refined, segregated, and uploaded to an MS Excel spreadsheet and analyzed by SPSS version 23 in Windows format. The continuous variables were represented as frequency, mean, standard deviation, and percentages. The categorical variables were calculated by Pearson's Chi-square test for p values. The values of p (<0.05) were considered as significant. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FIT were calculated with 95% confidence intervals.

A total of n=100 cases were included in the study for analysis. The baseline demographics and risk profiles were comparable between the FIT and colonoscopy groups given in Table 1. The mean age was 58.4 ± 10.2 years in the FIT group and 59.1 ± 9.8 years in the colonoscopy group. Gender distribution was nearly equal across both groups. Risk factors such as family history of colorectal cancer, smoking, and obesity were similarly distributed, with a slightly higher prevalence of family history and obesity in the colonoscopy group. This balanced baseline ensures that the diagnostic performance comparison between FIT and colonoscopy is not confounded by demographic or risk factor imbalances.

Table 2 shows the diagnostic performance of FIT versus colonoscopy. A critical analysis of the table shows that FIT demonstrated a high diagnostic accuracy with a sensitivity of 90% and specificity of 88%, closely approaching colonoscopy's perfect diagnostic profile. In this study, FIT yielded 45 true positives and 44 true negatives, but also recorded 6 false positives and 5 false negatives. Despite these discrepancies, FIT showed strong predictive values: a PPV of 88.2% and an NPV of 89.8%. While colonoscopy remains the gold standard with 100% values across all metrics, FIT still offers reliable detection, especially in large-scale population screening scenarios where resource constraints are a concern.

Table 3 shows the FIT performance varied by cancer stage. The results show that sensitivity was highest for Stage III cancers, detecting all 18 cases (100%). Detection remained strong for Stage II (93.8%) and Stage I (83.3%) cancers, though two early-stage cases were missed. Moreover, only 50% of Stage IV cases were detected by FIT, indicating reduced sensitivity in advanced disease, possibly due to intermittent or non-bleeding tumors. These results suggest FIT is most effective in detecting moderate-stage colorectal cancer and underscores the importance of follow-up colonoscopy for negative FIT results in high-risk populations.

Analysis of Table 4 reveals the common causes of diagnostic errors that occur through false FIT results. Hemorrhoids along with inflammatory bowel conditions including ulcerative colitis appeared in six false positive tests because of their capacity to cause occult bleeding. The condition diverticulosis also resulted in incorrect positive FIT test results. Right-sided lesions were the main cause of false negative results because they deteriorate hemoglobin while traveling through the stool. The tests managed to miss two small cancers (microadenomas) showing that FIT does not perform well at detecting low-volume or non-bleeding lesions in the colon. An ongoing assessment with colonoscopy must take place whenever physicians continue to suspect a patient has colorectal cancer.

Table 5 shows the patient compliance and preferences for the evaluation methods. FIT showed superior patient compliance and acceptability. The completion rate was 100% for FIT compared to 92% for colonoscopy, with four individuals declining colonoscopy due to bowel preparation discomfort. Patient satisfaction was significantly higher for FIT, with 96% finding it easy to use and 94% willing to repeat the test, compared to 60% and 70%, respectively, for colonoscopy. These findings underline FIT's value as a preferred, user-friendly screening tool that may enhance participation in colorectal cancer screening programs, especially among asymptomatic individuals.

The present study was done to compare the diagnostic accuracy of fecal immunochemical test (FIT) versus colonoscopy for the detection of colorectal cancer (CRC) screening. The overall findings of this study suggested that FIT is a good substitute and offers a viable non-invasive alternative with relatively high sensitivity, and specificity with higher patient compliance and satisfaction however, it is not a perfect substitute for colonoscopy. Our study was conducted for 100 participants equally divided between FIT and colonoscopy groups. As given in Table 1, baseline demographics and risk profiles were well-balanced across both groups. The mean ages of both groups were comparable and the gender distribution was nearly equal. The analysis of key risk factors such as the family history of CRC, smoking, and obesity was similarly distributed, minimizing the likelihood of bias that could influence the diagnostic outcomes. We found that the fecal immunochemical test (FIT) performed compared to colonoscopy for CRC screening through accuracy assessment and patient acceptance evaluations. The research findings show that FIT provides a good non-invasive screening method with sensitivity and specificity rates that match well with colonoscopy at the same time patients adhere to the testing process. The FIT was able to achieve a sensitivity of 90% and a specificity of 88%. This was in agreement with previous studies in this field where they found the sensitivity ranging from 79% to 94% and specificity from 85% to 95% [10, 11]. Colonoscopy remains the cornerstone for the diagnosis of CRC because of its excellent diagnostic performance. The FIT's performance appears to be clinically meaningful, especially considering the accessibility and non-invasive nature. From the FIT screening model of this study, a total of 45 patients received accurate positive results, while 44 received accurate negative results and six patients were misdiagnosed as positive but only five received accurate negative results. The study data reflected a positive predictive value of 88.2% and a negative predictive value of 89.8% which confirms FIT's effectiveness for screening programs. The important consideration of this study was the stage-wise breakdown of FIT performance depicted in Table 3. We found that FIT showed the highest sensitivity in stage III cancers (100%) followed by stage II (93.8%) and stage I (83.3%). However, the sensitivity dropped to 50% in stage IV cases. While the results appear to be contradictory this pattern is consistent with literature indicating that the advanced tumors may not always bleed continuously or their bleeding may be considerably decreased thereby reducing its chances of being detected by FIT analysis [8, 12].  Early-stage cancer detection through FIT tests produces lower results yet remains helpful because it enables timely treatment of such conditions. The high detection success rates for Stage II and Stage III cancers demonstrate that FIT serves well in detecting CRC before it becomes untreatable. Table 4 shows the reasons for diagnostic errors associated with FIT analysis. Hemorrhoids and IBD such as ulcerative colitis are the primary causes for false positive reporting because this can produce occult bleeding in the absence of malignancy. We found that diverticulosis also contributed to false positive results. Among the false negatives, right-sided lesions were the major factor. The possible reason could be due to hemoglobin degradation during transit through the colon reducing the chances of detection [13]. In addition, FIT failed to detect two cases of microadenomas which highlights its limited efficacy in identifying small, non-bleeding lesions. This shows that while FIT can be a valuable first-line tool it must be followed by colonoscopy, especially in cases with high clinical suspicion. Our study showed that patient compliance and preferences favored FIT and the completion rate was 100% versus 92% for the colonoscopy examination because four participants refused bowel preparation. FIT was also rated easier to use by the participants (96% vs. 60%) and more participants were willing to repeat it (94% vs. 70%). These differences underscore an important advantage of FIT evaluation and its acceptability. Because adherence is a critical determinant of screening success at the population level, a test that is easier, less invasive, and more acceptable can lead to better participation rates and earlier detection of disease [14].

In conclusion, while colonoscopy remains the definitive diagnostic and therapeutic tool for colorectal cancer screening, FIT offers a practical, accurate, and patient-preferred alternative. Its performance is especially notable in detecting Stage II and III cancers. However, its limitations particularly in detecting right-sided and early-stage tumors highlight the need for integrated strategies that combine FIT with targeted colonoscopy follow-up in high-risk cases. Widespread implementation of FIT, particularly in low-resource settings, could significantly improve screening coverage, and early detection, and ultimately reduce colorectal cancer mortality.

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