Faecal immunochemical tests for haemoglobin: Analytical challenges and potential solutions

Stable hemoglobin concentration with fecal immunochemical test at high temperatures in a Caribbean colorectal cancer screening program

BACKGROUND AND AIMS

High temperatures may reduce fecal immunochemical test (FIT) positivity and colorectal cancer (CRC) detection sensitivity. We investigated the effect of temperature on hemoglobin concentration [Hb], in the FOB Gold®. Additionally, we examined FIT pick-up, storage, return times and specimen collection.

MATERIALS AND METHODS

In vitro experiments with buffer containing FIT devices, inoculated with Hb-spiked stool. For 7 days, 144 samples were stored in groups of 36 at 4 °C, 22 °C, 30 °C, and 50 °C. Additionally, 54 samples were stored in groups of 18 at 34 °C, 42 °C and 50 °C for 20 h. Paired t-tests and repeated measure ANOVA assessed [Hb] change. Sixty-five screening participants completed a FIT-handling questionnaire.

RESULTS

After 7 days, mean [Hb] was stable at 30 °C (0.8 µg Hb/g;95 %CI: -1.5 to 3.1;p = 0.50). For 50 °C, mean [Hb] decreased within 2 days (-21.3 µg Hb/g;95 %CI: -30.2 to -12.5;p < 0.001) and after 20 h (-63.0 µg Hb/g;95 %CI: -88.7 to -37.3;p < 0.001), respectively. All other temperature categories showed significant mean [Hb] increase. Same-day FIT return was reported by 80 %. Eighty-seven percent experienced specimen collection as easy and 33 % kept the FIT refrigerated after collection.

CONCLUSIONS

The FOB Gold® is suitable for CRC screening in tropical climates. Although most respondents indicated same-day sample return, we recommend avoiding FIT storage above 30 °C for longer than7 days.

Precision Colorectal Cancer Fecal Immunological Test Screening With Fecal-Hemoglobin-Concentration-Guided Interscreening Intervals

Importance

Given a gradient relationship between fecal hemoglobin (f-Hb) concentration and colorectal neoplasia demonstrated previously, using f-Hb-guided interscreening interval has increasingly gained attention in population-based fecal immunological test (FIT), but it is very rare to address how to implement such a precision strategy and whether it can economize the use of FIT and colonoscopy.

Objective

To demonstrate the applicability of personalized colorectal cancer (CRC) screening with f-Hb-guided screening intervals to reduce the number of FITs and colonoscopy with as equivalent efficacy as universal biennial screening.

Design, Setting, and Participants

A retrospective cohort study for developing f-Hb-guided precision interscreening interval was conducted using data on a Taiwanese biennial nationwide FIT screening program that enrolled more than 3 million participants aged 50 to 74 years between 2004 and 2014. The cohort was followed up over time until 2019 to ascertain colorectal neoplasia and causes of death. A comparative study was further designed to compare the use of FIT and colonoscopy between the personalized f-Hb-guided group and the universal biennial screening group given the equivalent efficacy of reducing CRC-related outcomes.

Main Outcomes and Measurements

A spectrum of f-Hb-guided intervals was determined by using the Poisson regression model given the equivalent efficacy of a universal biennial screening. The use of FIT and colonoscopy for the pragmatic f-Hb-guided interval group was measured compared with the universal biennial screening group. Data analysis was performed from September 2022 to October 2023.

Results

Using data from the 3 500 250 participants (mean [SD] age, 57.8 [6.0] years) enrolled in the Taiwanese biennial nationwide FIT screening program, an incremental increase in baseline f-Hb associated with colorectal neoplasia and CRC mortality consistently was observed. Participants with different f-Hb levels were classified into distinct risk categories. Various screening intervals by different f-Hb levels were recommended. Using the proposed f-Hb-guided screening intervals, it was found that the personalized method was imputed to reduce the number of FIT tests and colonoscopies by 49% and 28%, respectively, compared with the universal biennial screening.

Conclusion and Relevance

The gradient relationship between f-Hb and colorectal neoplasia and CRC mortality was used to develop personalized FIT screening with f-Hb-guided screening intervals. Such a precision interscreening interval led to the reduced use of FIT test and colonoscopy without compromising the effectiveness of universal biennial screening.

Faecal Immunochemical Test (FIT) Sensitivity; A Five Year Audit

Introduction: Colorectal cancer has a high prevalence and mortality rate in the United Kingdom. Cancerous colorectal lesions often bleed into the gastrointestinal lumen. The faecal immunochemical test (FIT) detects haemoglobin (Hb) in the faeces of patients and is used as a first line test in the diagnosis of colorectal cancer. Materials and Methods: A retrospective audit of all FIT performed and all colorectal cancers diagnosed in the Hull and East Riding of Yorkshire counties of the United Kingdom (population approximately 609,300) between 2018 and 2022 was conducted. FIT were performed using a HM-JACKarc analyser from Kyowa medical. The predominant symptom suggestive of colorectal cancer which prompted the FIT was recorded. Colorectal cancer was diagnosed using the gold standard of histological biopsy following colonoscopy. Results: Between 2018 and 2022, 56,202 FIT were performed on symptomatic patients. Follow on testing identified 1,511 with colorectal cancer. Of these people, only 450 people with a confirmed colorectal cancer had a FIT within the 12 months preceding their diagnosis. Of these 450 FIT results, 36 had a concentration of <10 μg/g and may be considered to be a false negative. The sensitivity of FIT in the patients identified was 92.00%. The most common reason stated by the clinician for a FIT being performed in patients with colorectal cancer was a change in bowel habits, followed by iron deficient anaemia. The number of patients diagnosed with colorectal cancer decreased in 2020, but increased significantly in 2021. Discussion: This study shows that 8.00% of people diagnosed with colorectal cancer in the Hull and East Riding of Yorkshire regions had a negative FIT. This study also shows that the SARS-CoV-2 pandemic affected the number of people diagnosed with colorectal cancer, and therefore skews the prevalence and pre-test probability of a positive test. There are many reasons why a FIT could produce a false negative result, the most likely being biological factors affecting the stability of haemoglobin within the gastrointestinal tract, or pre-analytical factors influencing faecal sampling preventing the detection of haemoglobin. Some colorectal lesions do not protrude into the gastrointestinal lumen and are less likely to bleed. Conclusion: This is the first study showing data from outside of a structured clinical trial and provides the largest study to date showing the sensitivity of FIT in a routine clinical setting. This study also provides evidence for the impact COVID-19 had on the rate of colorectal cancer diagnosis.

Interval cancers in a national colorectal screening programme based on faecal immunochemical testing: Implications for faecal haemoglobin concentration threshold and sex inequality

OBJECTIVE

To compare interval cancer proportions (ICP) in the faecal immunochemical test (FIT)-based Scottish Bowel Screening Programme (SBoSP) with the former guaiac faecal occult blood test (gFOBT)-based SBoSP and investigate associations between interval cancer (IC) and faecal haemoglobin concentration (f-Hb) threshold, sex, age, deprivation, site, and stage.

METHODS

The ICP data from first year of the FIT-based SBoSP and the penultimate year of the gFOBT-based SBoSP were compared in a prospective cohort design.

RESULTS

With FIT, 801 colorectal cancers (CRCs) were screen detected (SDC), 802 were in non-participants, 548 were ICs, 39 were colonoscopy missed and 72 were diagnosed after incomplete screening; with gFOBT: 540, 904, 556, 45, and 13, respectively. FIT had a significantly higher proportion of SDC compared to IC than gFOBT. For FIT and gFOBT, ICP was significantly higher in women than men. As f-Hb threshold increased, ICP increased and, for any f-Hb threshold for men, a lower threshold was required for comparable ICP in women. In Scotland, the current threshold of ≥80 µg Hb/g faeces would have to be lowered to ≥40 µg Hb/g faeces for women to achieve sex equality for ICP. In the FIT-based SBoSP, there were four times as many stage I SDC than IC. This was reversed in advanced stages, with twice as many stage IV CRC diagnosed as IC versus SDC.

CONCLUSIONS

Reducing the numbers of IC requires lowering the f-Hb threshold. Using different f-Hb thresholds for women and men could eliminate the sex disparity, but with additional colonoscopy.

Breath Fingerprint of Colorectal Cancer Patients Based on the Gas Chromatography-Mass Spectrometry Analysis

The human body emits a multitude of volatile organic compounds (VOCs) via tissues and various bodily fluids or exhaled breath. These compounds collectively create a distinctive chemical profile, which can potentially be employed to identify changes in human metabolism associated with colorectal cancer (CRC) and, consequently, facilitate the diagnosis of this disease. The main goal of this study was to investigate and characterize the VOCs' chemical patterns associated with the breath of CRC patients and controls and identify potential expiratory markers of this disease. For this purpose, gas chromatography-mass spectrometry was applied. Collectively, 1656 distinct compounds were identified in the breath samples provided by 152 subjects. Twenty-two statistically significant VOCs (p-xylene; hexanal; 2-methyl-1,3-dioxolane; 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; hexadecane; nonane; ethylbenzene; cyclohexanone; diethyl phthalate; 6-methyl-5-hepten-2-one; tetrahydro-2H-pyran-2-one; 2-butanone; benzaldehyde; dodecanal; benzothiazole; tetradecane; 1-dodecanol; 1-benzene; 3-methylcyclopentyl acetate; 1-nonene; toluene) were observed at higher concentrations in the exhaled breath of the CRC group. The elevated levels of these VOCs in CRC patients' breath suggest the potential for these compounds to serve as biomarkers for CRC.

Comparison and commutability study among four faecal immunochemical tests (FIT) systems

OBJECTIVES

Faecal immunochemical tests for haemoglobin (FIT) are used in colorectal cancer screening programs around the world and increasingly for triage of symptomatic patients. FIT results are currently not traceable to a common reference standard and results obtained on various FIT systems may not be equivalent. The size of the bias between the systems is difficult to quantify due to the complex pre-analytical aspects of FIT.

METHODS

This study aimed to quantify the bias and the correlation between four FIT systems by measuring a panel of 38 faecal samples while limiting the effect of the pre-analytical aspects. In addition, the commutability of seven candidate reference materials (RM) was assessed.

RESULTS

Pairwise method comparisons based on faecal samples demonstrated Pearson correlation coefficients ranging between 0.944 and 0.970 and an average proportional bias of -30 to -35 % for one FIT system compared to the other three. The relative standard deviation among biases of the individual samples was around 20 %. Due to these sample specific differences, no decisive conclusions could be drawn in the commutability study. However, two candidate RMs, prepared in the FIT system-specific storage/extraction buffers, had a better commutable profile than the other five.

CONCLUSIONS

The use of a common threshold for all FIT systems is currently not possible due to the presence of a proportional bias. We have identified potential commutable RMs to take to further studies on the production of a common calibrator, with the aim being to reduce the analytical bias observed on different FIT systems.

Faecal haemoglobin: Measurement, applications, and future potential

Faecal hemoglobin concentrations (f-Hb) can be quantitated using faecal immunochemical test for haemoglobin (FIT) analytical systems. FIT are of proven value and widely used in colorectal cancer (CRC) screening. Several factors affect f-Hb including sex, age, deprivation, geographical region, and FIT system. Thus, FIT data may not be transferable. Women are disadvantaged in programmes using a single f-Hb threshold for all participants, but risk scoring or sex stratified thresholds could be used to minimise this problem. In addition, low but detectable f-Hb, below the threshold, implies future risk of CRC. In several countries, where colonoscopy resources are constrained, FIT are now accepted as of added value in assessment of patients presenting in primary or secondary care with symptoms, although some serious colorectal disease is missed. Elevated f-Hb in the absence of any discernible colorectal lesions is common and has been found in several diseases with a systemic inflammatory component, including circulatory, respiratory, digestive, neuropsychological, blood and endocrine diseases, and others. There is growing evidence for the value of f-Hb in post-polypectomy surveillance, potentially saving costs and colonoscopy. There may be a role for FIT systems which have lower limits of detection than currently available methods. The faecal material remaining in FIT specimen collection devices could be used for further studies, including assessment of the microbiome. The estimation of f-Hb is now a mature investigative tool but further research will undoubtedly expand applications of value.

An observational study of replicate faecal immunochemical tests in the urgently referred symptomatic cohort

INTRODUCTION

Triage of patients with suspected colorectal cancer (CRC) utilises a single faecal immunochemical test (FIT) at a defined threshold. Limited evidence exists regarding whether replicate FIT improves the positive and negative predictive value in symptomatic patients. This study examines urgently referred symptomatic patients undergoing replicate FIT. Primary aim is to assess two FITs and CRC/serious bowel disease. Secondary aims are to determine correlation and utility of replicate FIT.

METHODOLOGY

Patients carried out one additional FIT during COVID-19 pandemic. FIT 1 and FIT 2 (the replicate sample) were analysed in relation to symptoms, diagnoses, investigations, future colonoscopy and missed CRC. Study period was 01/03/2020-31/07/2020. Three subgroups were compared; double positive (≥10 μg Hb/g faeces), double negative, and discordant FIT (one positive).

RESULTS

111 patients had replicate FIT (50 male, 61 female). 43 (38.7%) patients had double negative, 32 (28.8%) double positive and 36 (32.4%) had discordant FITs. Median time between FITs was 14 days (IQR = 11-19). 83% of double positive patients underwent colonoscopy/virtual colonoscopy (61% in double negative patients). Six CRC and one high-risk polyp were in double positive patients (none in other groups). One discordant patient was not investigated and a CRC missed.

CONCLUSIONS

Replicate FIT as a triage strategy appears most effective where both FITs are negative. CRC risk is low when FIT results are discordant. Double negative FITs are reassuring given benign associated diagnoses, or for patients where endoscopic investigation is high-risk. Larger studies are required to evaluate discordant FITs, enabling refinement of urgent investigation pathways.

Strategies to minimise the current disadvantages experienced by women in faecal immunochemical test-based colorectal cancer screening

Currently, women are disadvantaged compared to men in colorectal cancer (CRC) screening, particularly in programmes that use faecal immunochemical tests for haemoglobin (FIT) followed by colonoscopy. Although there is no single cause for all the known disadvantages, many can be attributed to the ubiquitous finding that women have lower faecal haemoglobin concentrations (f-Hb) than men; there are many plausible reasons for this. Generally, a single f-Hb threshold is used in CRC screening programmes, leading to lower positivity for women than men, which causes poorer outcomes for women, including lower CRC detection rate, higher interval cancer (IC) proportion, and higher CRC mortality. Many of the now widely advocated risk scoring strategies do include factors taking account of sex, but these have not been extensively piloted or introduced. Using different f-Hb thresholds for the sexes seems advantageous, but there are difficulties, including deciding which characteristic should be selected to achieve equivalency, for example, positivity, IC proportions, or specificity. Moreover, additional colonoscopy resources, often constrained, would be required. Governments and their agencies should be encouraged to prioritise the allocation of resources to put simple strategies into practice, such as different f-Hb thresholds to create equal positivity in both sexes.

Faecal immunochemical testing (FIT) in patients with signs or symptoms of suspected colorectal cancer (CRC): a joint guideline from the Association of Coloproctology of Great Britain and Ireland (ACPGBI) and the British Society of Gastroenterology (BSG)

Faecal immunochemical testing (FIT) has a high sensitivity for the detection of colorectal cancer (CRC). In a symptomatic population FIT may identify those patients who require colorectal investigation with the highest priority. FIT offers considerable advantages over the use of symptoms alone, as an objective measure of risk with a vastly superior positive predictive value for CRC, while conversely identifying a truly low risk cohort of patients. The aim of this guideline was to provide a clear strategy for the use of FIT in the diagnostic pathway of people with signs or symptoms of a suspected diagnosis of CRC. The guideline was jointly developed by the Association of Coloproctology of Great Britain and Ireland/British Society of Gastroenterology, specifically by a 21-member multidisciplinary guideline development group (GDG). A systematic review of 13 535 publications was undertaken to develop 23 evidence and expert opinion-based recommendations for the triage of people with symptoms of a suspected CRC diagnosis in primary care. In order to achieve consensus among a broad group of key stakeholders, we completed an extended Delphi of the GDG, and also 61 other individuals across the UK and Ireland, including by members of the public, charities and primary and secondary care. Seventeen research recommendations were also prioritised to inform clinical management.

A comparison of the faecal haemoglobin concentrations and diagnostic accuracy in patients suspected with colorectal cancer and serious bowel disease as reported on four different faecal immunochemical test systems

OBJECTIVES

Faecal immunochemical tests for haemoglobin (FIT) are used in colorectal cancer (CRC) screening programmes and to triage patients presenting with symptoms suggestive of CRC for further bowel investigations. There are a number of quantitative FIT analytical systems available. Currently, there is no harmonisation or standardisation of FIT methods. The aim of the study was to assess the comparability of numerical faecal haemoglobin concentrations (f-Hb) obtained with four quantitative FIT systems and the diagnostic accuracy at different f-Hb thresholds.

METHODS

A subgroup of the National Institute for Health and Care Excellence (NICE) FIT study, a multicentre, prospective diagnostic accuracy study were sent four FIT specimen collection devices from four different FIT systems or two FIT devices for one FIT system. Faecal samples were examined and analysis of results carried out to assess difference between methods at thresholds of limit of detection (LoD), 10 µg haemoglobin/g faeces (µg/g) and 100 μg/g.

RESULTS

233 patients returned specimen collection devices for examination on four different systems; 189 patients returned two FIT kits for one system. At a threshold of 100 μg/g the sensitivity is the same for all methods. At lower thresholds of LoD and 10 μg/g differences were observed between systems in terms of patients who would be referred and diagnostic accuracies.

CONCLUSIONS

The lack of standardisation or harmonisation of FIT means that differences are observed in f-Hb generated on different systems. Further work is required to understand the clinical impact of these differences and to minimise them.

Evaluation of the Sentinel-FOB gold faecal immunochemical test for the presence of haemoglobin using the automated Roche Cobas 8000 system

Objectives

Design

Results

Conclusion

•

The SENTIFIT-FOB Gold assay for the quantitation of haemoglobin in faeces was evaluated on the widely used automated Roche Cobas 8000 system.

•

Good analytical and clinical performance were confirmed.

•

The diagnostic accuracy was assessed and the optimal cutoff for use in symptomatic patients was determined.

Comparison of the QuikRead go® point-of-care faecal immunochemical test for haemoglobin with the FOB Gold Wide® laboratory analyser to diagnose colorectal cancer in symptomatic patients

OBJECTIVES

Faecal immunochemical testing for haemoglobin (FIT) is used to triage patients for colonic investigations. Point-of-care (POC) FIT devices on the market have limited data for their diagnostic accuracy for colorectal cancer (CRC). Here, a POC FIT device is compared with a laboratory-based FIT system using patient collected samples from the urgent referral pathway for suspected CRC.

METHODS

A prospective, observational cohort study. Patients collected two samples from the same stool. These were measured by POC QuikRead go^® (Aidian Oy, Espoo, Finland) and laboratory-based FOB Gold Wide^® (Sentinel Diagnostics, Italy). Faecal haemoglobin <10 μg haemoglobin/g of faeces was considered as negative. At this threshold, comparisons between the two systems were made by calculating percentage agreement and Cohen's kappa coefficient. Proportion of negative results were compared with Chi squared testing. Sensitivities for CRC were calculated.

RESULTS

A total of 629 included patients provided paired samples for FIT to compare the QuikRead go^® and FOB Gold Wide^®. The agreement around the negative threshold was 83.0% and Cohen's kappa coefficient was 0.54. The QuikRead go^® reported 440/629 (70.0% of samples) as negative compared to 523/629 (83.1%) for the FOB Gold Wide^®, this difference was significant (p-value<0.001). Sensitivities for CRC detection by the QuikRead go^® and FOB Gold Wide^® were 92.9% (95% confidence interval (CI): 68.5-98.7%) and 100% (CI: 78.5-100%) respectively.

CONCLUSIONS

Both systems were accurate in their ability to detect CRC. Whilst good agreement around the negative threshold was identified, more patients would be triaged to further colonic investigation if using the QuikRead go^®.

Faecal immunochemical test to triage patients with possible colorectal cancer symptoms: meta-analysis

BACKGROUND

This review evaluated the utility of single quantitative faecal immunochemical test (FIT) as a triaging tool for patients with symptoms of possible colorectal cancer, the effect of symptoms on FIT accuracy, and the impact of triaging incorporating FIT on service provision.

METHODS

Five databases were searched. Meta-analyses of the extracted FIT sensitivities and specificities for detection of colorectal cancer at reported f-Hb thresholds were performed. Secondary outcomes included sensitivity and specificity of FIT for advanced colorectal neoplasia and serious bowel disease. Subgroup analysis by FIT brand and symptoms was undertaken.

RESULTS

Fifteen prospective cohort studies, including 28 832 symptomatic patients were included. At the most commonly reported f-Hb positivity threshold of ≥ 10 µg Hb/g faeces (n=13), the summary sensitivity was 88.7% (95% c.i. 85.2 to 91.4) and the specificity was 80.5% (95% c.i. 75.3 to 84.8) for colorectal cancer. At lower limits of detection of ≥ 2 µg Hb/g faeces, the summary sensitivity was 96.8% (95% c.i. 91.0 to 98.9) and the specificity was 65.6% (95% c.i. 59.0 to 71.6). At the upper f-Hb positivity thresholds of ≥ 100 µg Hb/g faeces and ≥ 150 µg Hb/g faeces, summary sensitivities were 68.1% (95% c.i. 59.2 to 75.9) and 66.3% (95% c.i. 52.2 to 78.0), with specificities of 93.4% (95% c.i. 91.3 to 95.1) and 95.1% (95% c.i. 93.6 to 96.3) respectively. FIT sensitivity was comparable between different assay brands. FIT sensitivity may be higher in patients reporting rectal bleeding.

CONCLUSION

Single quantitative FIT at lower f-Hb positivity thresholds can adequately exclude colorectal cancer in symptomatic patients and provides a data-based approach to prioritization of colonoscopy resources.

Faecal haemoglobin concentrations in women and men diagnosed with colorectal cancer in a national screening programme

Objective

There is evidence that colorectal cancer screening using faecal haemoglobin is less effective in women than men. The faecal haemoglobin concentrations were therefore examined in women and men with screen-detected colorectal cancer.

Setting

Scottish Bowel Screening Programme, following the introduction of a faecal immunochemical test from November 2017, to March 2020.

Methods

Data were collated on faecal haemoglobin concentrations, pathological stage and anatomical site of the main lesion in participants who had colorectal cancer detected. The data in women and men were compared.

Results

For the faecal haemoglobin concentrations studied (>80 µg Hb/g faeces), the distributions indicated lower concentrations in women. Marked differences were found between women and men diagnosed with colorectal cancer. The median faecal haemoglobin concentration for women (n = 720) was 408 µg Hb/g faeces compared to 473 µg Hb/g faeces for men (n = 959) (p = 0.004) and 50.6% of the results were >400 µg Hb/g faeces in women; in men, this was 57.8%. The difference in faecal haemoglobin concentrations in women and men became less statistically significant as stage advanced from stages I–IV. For right-sided, left-sided and rectal colorectal cancer, a similar gender difference persisted in all sites. Differences in faecal haemoglobin between the genders were significant for left-sided cancers and stage I and approached significance for rectal cancers and stage II, but all sites and stages showed lower median faecal haemoglobin concentrations for women.

Conclusions

To minimise gender inequalities, faecal immunochemical test-based colorectal cancer screening programmes should evaluate a strategy of using different faecal haemoglobin concentration thresholds in women and men.

Faecal immunochemical testing (FIT): sources of result variation based on three years of routine testing of symptomatic patients in English primary care

Introduction: We aimed to determine the analytical capabilities of a commonly used faecal immunochemical test (FIT) to detect faecal haemoglobin (Hb) in symptomatic people attending primary care in the context of the English NICE DG30 guidance.Materials and Methods: Data obtained from independent verification studies and clinical testing of the HM-JACKarc FIT method in routine primary care practice were analysed to derive performance characteristics.Results: Detection capabilities for the FIT method were 0.5 µg/g (limit of blank), 1.3 µg/g (limit of detection) and 3.0 µg/g (limit of quantitation). Of 33 non-homogenized specimens, 31 (93.9%) analysed in triplicate were consistently categorized relative to 10 µg/g, compared to all 33 (100%) homogenized specimens. Imprecision was higher (median 27.8%, (range 20.5% to 48.6%)) in non-homogenized specimens than in homogenized specimens (10.2%, (7.0 to 13.5%)). Considerable variation was observed in sequential clinical specimens from individual patients but no positive or negative trend in specimen degradation was observed over time (p = 0.26).Discussion: The FIT immunoassay evaluated is capable of detecting faecal Hb at concentrations well below the DG30 threshold of 10 µg/g and is suitable for application in this context. The greatest practical challenge to FIT performance is reproducible sampling, the pre-analytical step associated with most variability. Further research should focus on reducing sampling variability, particularly as post-COVID-19 guidance recommends greater FIT utilization.