The current guidelines by the American Gastroenterology Association suggest that fecal occult blood tests should only be used to screen for colorectal cancer (CRC) in average risk, asymptomatic outpatients.[7, 8] [9] As a non-invasive, easily administered and relatively inexpensive test, the FOBT has become a frequently used screening modality for CRC screening across the world.[10] [11, 12] However, the widespread availability of FOBTs has also resulted in their use beyond their sole validated purpose for CRC screening.[13, 14]. Despite little or no evidence to support the utility of FOBTs in hospitalized patients, studies demonstrate continued inappropriate use in inpatient settings .[15] [16].[17] Notably, FOBTs are frequently used in the evaluation of anemia in hospital settings and we focused our investigation in this population.[3, 17, 18] While differences in inclusion criteria make it difficult to assess the prevalence of this practice, in our sample, 12.9% (n = 817) of patients who developed a drop in hemoglobin > 2g/dl underwent an FOBT. Most patients (65.3%) did not have overt GI bleeding. Concomitant use of certain medications (e.g., acetylsalicylic acid, non-steroidal anti-inflammatory agents, Vitamin C, selective serotonin reuptake inhibitors) and certain foods (e.g., red meat, broccoli, turnips and radishes) can interfere with FOBTs and result in false positive results.[19, 20] Both anemia and the invalidators of FOBTs are common during hospitalization.[4] Given the potential consequences of exposing patients to the risk of unnecessary endoscopic procedures, clinicians should carefully consider the multiple causes of hospital acquired anemia, including blood draws, medications, and bone marrow suppression secondary to acute infections and illness before reflexive ordering of an FOBT.[21, 22]
The use of FOBTs in the setting of overt GI bleeding is also problematic. Rationally, the presence of overt blood should preclude the need for testing for occult blood. Rates of FOBTs performed in the context of overt GI bleed range from 5%- 23%.[3, 23] In our sample, 34.6% of those who had FOBTs performed in the setting of a drop in hemoglobin had a history consistent with GI bleed. We also noted a mismatch between the documentation of symptoms consistent with a GI bleed and nursing documentation of stool appearance although this may be limited by the absence of documentation in more than half the cases evaluated. Limitations in stool documentation in addition to possible under-utilization of digital rectal examinations to confirm histories may drive inappropriate FOBTs. (18,19) Understanding these drivers of potentially inappropriate testing may help us improve processes and practices.
Previous reports have described variable impacts of FOBT results on subsequent management including delays in care while awaiting testing results, no changes in management and increases in endoscopic procedures.[3, 4, 18, 23] We evaluated patients with and without symptoms of overt GI bleeding separately and found that FOBT results were associated with subsequent endoscopic procedures only in those without overt GI bleeding - where those with a positive FOBT result were more likely to undergo endoscopic evaluation. No association was noted between FOBT results and endoscopy rates in patients with overt GI bleeding. Clinicians may appropriately disregard negative test results when the history is strongly suggestive of a GI bleed but when faced with diagnostic uncertainty, positive FOBT results may lead to confirmation bias and subsequent endoscopic evaluation. We also noted that those with lower hemoglobin values were more likely to have undergone endoscopy regardless of symptoms of GI bleeding. It is likely that clinicians weigh the degree of anemia heavily in their decision to pursue diagnostic endoscopic evaluation.[24] Further study of the interplay between FOBT results, the degree of anemia, subsequent endoscopies and outcomes will help clinicians understand their own cognitive processes and decrease the risk of potentially avoidable procedures.
Interestingly, among patients without overt GI bleeding, we found a higher diagnostic yield from endoscopic procedures with positive FOBT results compared to those with negative FOBTs. The most common pathology found in patients without overt GI bleeding were gastric and duodenal ulcers. It is possible that these lesions bleed intermittently without reaching the threshold of overt GI bleeding. [18] These findings raise the question of whether there are selected clinical scenarios in which FOBTs in the inpatient setting may be helpful.
Our work has certain limitations. It is a single center’s experience, and our findings may not be generalizable. We assigned patients to the category of overt GI bleed based on the symptoms documented rather than findings on a digital rectal exam. We started with patients who developed a drop in hemoglobin and therefore cannot comment on inpatient FOBT use driven by other causes. Since this is a retrospective observational study, involving smaller number of patients, we could not do cost-effective analysis.
FOBTs continue to be utilized in inpatient settings for the evaluation of anemia and in those with overt GI bleeding. Understanding the drivers of FOBTs in the inpatient setting, including limitations in stool documentation and possible under-utilization of digital rectal examinations to confirm histories may help us improve processes and practices. Clinicians may appropriately disregard negative test results when the history is strongly suggestive of a GI bleed but when faced with diagnostic uncertainty, positive results may lead to subsequent potentially unnecessary endoscopic evaluation.