Lower Gastrointestinal Bleeding Workup

The 3 nonsurgical modalities used to diagnose lower gastrointestinal bleeding (LGIB) are colonoscopy, radionuclide scans, and angiography. Apart from colonoscopy, endoscopic procedures, such as esophagogastroduodenoscopy (EGD), wireless capsule endoscopy (WCE), push enteroscopy, and double-balloon enteroscopy, are used depending on the clinical circumstance. The sequence of using various modalities depends on such factors as rate of bleeding, hemodynamic status of the patient, and inability to localize bleeding with the initial modality.

Patients who have experienced multiple episodes of LGIB without a known source or diagnosis should undergo elective mesenteric angiography, upper and lower endoscopy, Meckel scanning, upper gastrointestinal (GI) series with small bowel, and enteroclysis. Elective evaluation of the entire GI tract may identify uncommon lesions and undiagnosed arteriovenous malformations (AVMs).

Ryan et al performed 17 elective provocative bleeding studies for occult LGIB in 16 patients.^[17] Although an abnormality was identified in 50% of patients, bleeding was provoked in 6 (37.5%) patients. Most of the positively provoked patients (ie, 5 patients) had a previously positive tagged red cell scintigraphy.^[17] Of the 6 patients with provoked bleeding, 3 were treated with superselective embolization at the time of provoked bleeding, 2 were treated with estrogen therapy, and 1 was treated with palliative therapy.^[17] Ten patients did not bleed during the provoked study.^[17]

Appropriate blood tests include a complete blood cell (CBC); serum electrolytes levels (eg, sequential multiple analysis 7 [SMA7]); and a coagulation profile, including activated partial thromboplastin time (aPTT), prothrombin time (PT), manual platelet count, and bleeding time.

Macari et al assessed the ability of computed tomography (CT) scanning to differentiate between intestinal ischemia and intramural hemorrhage and found that although some of the CT features overlap, ischemia typically involves a long segment with wall thickening of less than 1 cm, whereas intramural hemorrhage typically involves a short segment with wall thickening of 1 cm or greater.^[18] Diagnosis was confirmed by laboratory findings, clinical parameters, and follow-up examinations, or at surgery.

Helical CT scanning of the abdomen and pelvis can be used when a routine workup fails to determine the cause of active gastrointestinal (GI) bleeding.^[19] Multiple criteria, including vascular extravasation of the contrast medium, contrast enhancement of the bowel wall, thickening of the bowel wall, spontaneous hyperdensity of the peribowel fat, and vascular dilatations, are used to establish the bleeding site with helical CT scans.^{[20, 21]} The presence of diverticula alone is not enough to define the bleeding site.^[20]

Three-phase helical CT scanning should be performed using intravenous (IV) contrast. Water can be used as an oral contrast in the workup of patients who are actively bleeding.^[19]

A pilot study done in Sydney, Australia, to evaluate helical CT scanning as a diagnostic tool for acute LGIB suggested that this imaging modality is a safe, convenient, and accurate diagnostic tool relative to mesenteric angiography and colonoscopy.^[22] The authors proposed a new management algorithm for acute lower GI hemorrhage using helical CT scanning as the preselective mesenteric angiography screening tool.

Multidetector row CT (MDCT) scanning is also useful in the evaluation of LGIB.^[23] Frattaroli et al compared the sensitivity of MDCT scanning with endoscopy in identifying the site and etiology of acute UGIB and LGIB and reported that, in terms of identifying the anatomic location and etiology of UGIB, MDCT scanning had a sensitivity of 100% and 90.9%, respectively, whereas endoscopy had a sensitivity of 72.7% and 54.5%, respectively.^[24] For LGIB, MDCT had a sensitivity for site and etiology identification of 100% and 88.2%, respectively, whereas endoscopy had a sensitivity of 52.9% for both identifications.^[24]

In most patients with LGIB, colonoscopy is the initial diagnostic method of choice. Colonoscopy is successfully used to identify the origin of severe LGIB in approximately 74-82% of patients.^[8] In addition to its diagnostic utility, colonoscopy offers the opportunity for therapeutic intervention in the treatment of vascular ectasias, diverticular bleeding, neoplastic lesions, and ulcerative processes. Rapid colonic lavage with GoLYTELY (orally or by nasogastric [NG] tube) clears the intraluminal blood, clot, and stool, providing an adequate environment for visualization of the lower GI mucosa and lesions.

The 2008 SIGN guideline recommends the use of early colonoscopy to determine the cause and site of massive LGIB; the procedure can be used with CT scanning, CT angiography, or digital subtraction angiography. If colonoscopy fails to define the site of bleeding in patients with massive LGIB, angiographic transarterial embolization is recommended as an effective approach to control hemorrhage.^[13]

Colonoscopy has become the first choice of diagnostic modality following rapid purge with volume cathartics, such as GoLYTELY. Jensen and Machicado prospectively evaluated the role of urgent colonoscopy after purge in 80 consecutive patients with severe hematochezia and noted 74% of patients had colonic lesions, 11% had upper GI lesions, and 9% had presumed small bowel lesions; in 6%, no bleeding site was identified.^[25] Although the investigators recommended that EGD be performed before colonoscopy, upper and lower endoscopies can be performed simultaneously.

In another study, colonoscopy yielded a diagnosis in 90% of the patients, which provided opportunity for therapy at the same time. The patients who underwent colonoscopic evaluation had a significantly shorter hospital stay. Perform the urgent colonoscopy in the operating room or endoscopy suite on hemodynamically stable patients. If patients become unstable or colonoscopy reveals an active fulminant inflammation, abort the procedure.

Colonoscopy tends to result in improved patient outcomes. In patients who are hemodynamically stable with moderate to severe bleeding, diagnostic colonoscopy is the test of choice, because of its higher diagnostic yield and lower complication rate as compared with angiography.^{[25, 26]} The 2009 AAFP diverticular bleeding recommendations emphasize that urgent colonoscopy in the context of lower GI bleeding is safe.^[16]

Actively bleeding lesions can be treated with colonoscopic thermoregulation, epinephrine injection, photocoagulation, clip application, and a combination of these various methods.^[10] Incidentally discovered lesions should be left alone.

Candidate screening criteria

Candidates for colonoscopy should be properly screened and include patients who are hemodynamically stable with no ongoing brisk bleeding, because the diagnostic yield is lowered in such patient populations. Thus, the best candidates for colonoscopic evaluation are patients who are bleeding slowly or who have already stopped bleeding. The bowel should be well prepared, with a rapid oral purge (or via NG tube in selected patients), because performing a colonoscopy on an unprepared bowel is difficult and frequently unsuccessful. The bowel preparation does not reactivate or increase the rate of bleeding. In cases of suspected perforation or obstruction, plain abdominal radiography should be performed before colonoscopy to rule out these complications.

A randomized controlled trial comparing urgent versus elective colonoscopy was performed for patients with serious lower gastrointestinal bleeding. This study recommended that upper endoscopy should be performed initially to rule out an upper gastrointestinal source. This study also showed that the use of urgent colonoscopy does not improve the clinical outcome or cost of care when compared with elective colonoscopy in patients with serious hematochezia.^[27]

Advantages and disadvantages of colonoscopy

The advantages of colonoscopy include the following: (1) A bleeding lesion is localized in about 50-70% of patients; (2) definitive treatment, such as thermoregulation, epinephrine injection therapy, clip application, or laser photocoagulation, is possible during the procedure; (3) massively bleeding lesions that have stopped hemorrhaging are identified more often with colonoscopy than with angiography.

The disadvantages of colonoscopy include the following: (1) Colonoscopy must be performed by skilled endoscopists; (2) colonoscopy requires a bowel preparation that can cause a 3- to 4-hour delay; (3) a perforation during the examination is possible, particularly in a patient who is ill; (4) colonoscopy carries the risks of sedation for patients who are acutely bleeding; and (5) technical problems can make diagnosis and treatment more difficult.

The role of radionuclide scanning, or nuclear scintigraphic imaging, in the diagnosis and treatment of patients who present with LGIB remains controversial. Radionuclide scans include the technetium-99 ( ⁹⁹ Tc) sulfur colloid scan and the ^99m Tc pertechnetate–labeled autologous red blood cell scan (TRBC scan), as well as indium-111 ( ¹¹¹ In)–labeled RBC scintigraphy.

Nuclear scintigraphy is a sensitive diagnostic tool (86%) and can detect hemorrhage at rates as low as 0.1 mL/min (0.1-0.5 mL/min), as opposed to angiography, which detects bleeding at rates of 1-1.5 mL/min. This technique is reportedly 10 times more sensitive than mesenteric angiography in detecting ongoing bleeding, but it suffers from a low specificity (50%) compared with endoscopy or angiography due to its limited resolution; this has led many investigators to recommend that scintigraphic imaging be used primarily as a screening examination to select patients for mesenteric angiography. The 2008 SIGN guideline suggests nuclear scintigraphy may be effective in determining the source of bleeding in patients with significant recent hemorrhage.^[13]

Radionuclide scans frequently are performed before angiography, because the scans detect bleeding at a slower rate than what can be detected with angiography, thereby potentially eliminating the need for an invasive procedure.^[28] Negative findings on radionuclide scan make subsequent angiography less likely to be of benefit. In patients who are hemodynamically unstable and in patients with brisk ongoing LGIB, an angiography with or without a preceding radionuclide scan can be performed.

Ng and colleagues retrospectively reviewed the records 86 patients with positive TRBC scintigraphy findings and found that those with an immediate blush (within 2 min of the study) revealed a positive predictive value of 75% for angiography.^[29] However, patients with a delayed blush (after 2 min of the study) had a negative predictive value of 93% for angiography. Thus, patients with delayed blush should proceed with colonoscopic evaluation instead of mesenteric angiography. Use TRBC scintigraphy as a prescreening test for selective mesenteric angiography. The 2009 AAFP recommendations state that TRBC or arteriography may be used in patients with continued bleeding when endoscopy has not aided in making a diagnosis.^[16]

In a study by Ryan et al, TRBC scintigraphy identified the site of bleeding accurately in 9 patients with massive LGIB^[30] ; in 6 of 9 patients, the scintigraphy finding was positive in the first 5 minutes of the study. In 3 patients, the scintigraphy finding was positive at 14-45 minutes.

Emslie et al found that TRBC scanning is effective in localizing GI bleeding when positive within the continuous phase of imaging.^[28]

TRBC scans

The TRBC scan is preferred, because its half-life is longer and abdominal images can be obtained for up to 24 hours, which is advantageous in patients with intermittent bleeding. TRBC scans detect slow bleeds and have a sensitivity ranging from about 80% to 98%.^[31] The bleeding site can be identified accurately when intraluminal accumulation of TRBC is observed during the dynamic phase of scanning.

^99m Tc sulfur colloid scans

No preparation is required for ^99m Tc sulfur colloid. This agent has a very short half-life (2.5-3.5 min), because it is rapidly cleared by the reticuloendothelial system; as a result, images provided by such scans can be taken for the few minutes that the colloid is in circulation. However, these scans may not adequately demonstrate abnormalities in patients with intermittent bleeding. ^99m Tc sulfur colloid enhances the liver and spleen such that bleeding from both the hepatic flexures and the splenic flexures may be obscured.

¹¹¹ In-labeled RBC scintigraphy

The use of ¹¹¹ In–labeled RBC scintigraphy to detect intermittent bleeding has been described in the medical literature in a handful of publications. Ferrant and colleagues initially used ¹¹¹ In-labeled RBC scintigraphy in patients with lower GI bleeding in 1980,^[32] but this technique remains underutilized because of a prolonged half-life of 67 hours. It is also a more expensive and more labor-intensive technology than ^99m Tc labeling. Furthermore, the image quality and localization of bleeding can be less than desirable because of the prolonged half-life and intestinal motility.

Nonetheless, the longer half-life of ¹¹¹ In-labeled RBC scintigraphy can be useful in locating intermittent bleeding points, particularly when conventional methods have failed. Schmidt et al published a report on 6 patients in whom ^99m Tc scanning was initially unrewarding.^[33] Subsequent scintigraphy with ¹¹¹ In-labeled RBCs located the site of bleeding in all patients. In another study, Mole et al detected synchronous, small and large intestinal adenocarcinomas with ¹¹¹ In-labeled RBC scintigraphy in a 70-year-old patient with intermittent GI bleeding and profound blood loss anemia.^[34]

Advantages and disadvantages of radionuclide scanning

Advantages for radionuclide scans include their noninvasiveness and their high sensitivity. The disadvantages of radionuclide scans include the fact that the scans have a high false localization rate, ranging from approximately 3% to 59%.^[35] In 24 publications, the bleeding point was accurately localized in 52-90% of positive cases, with an average of 86% and incorrect localization of 14%. Because of the high false localization rate (10-60%) for the bleeding site, performing segmental resections based solely on scintigraphy results is not recommended. Another disadvantage of radionuclide scans is that the scans must be performed during active bleeding.

The difficulty of localization was demonstrated in a study by Hunter et al in which the results of TRBC scanning were incorrect in about 25% of patients^[36] ; 8 patients underwent unwarranted surgical procedures based upon the findings of more definitive tests. Poor localization of the source of the bleed in radionuclide scans often is due to the overlapping segments of bowel and the migration of tagged RBCs in the large bowel.

Recurrent lower GI bleeding occurs after negative TRBC scintigraphy. Hammond et al reported the overall rebleeding rate to be 27% and concluded that age, sex, bleeding source, use of anticoagulant/antiplatelet agents, length of hospital stay, admission hematocrit (Hct), Hct nadir, and transfusion requirements are not predictive of the patients who will rebleed.

In 1965, Baum et al described selective mesenteric angiography in the diagnosis of gastrointestinal (GI) bleeding.^[2] Since then, the value of mesenteric angiography in the diagnosis and management of LGIB has been well established.

Angiography is performed when active bleeding that precludes colonoscopy occurs and after colonoscopy has failed to identify a bleeding site. Selective mesenteric angiography can detect bleeding at a rate of more than 0.5 mL/min.

In a patient with active GI bleeding, the radiologist first cannulates the superior mesenteric artery, because most of the hemodynamically significant bleeding originates in the right colon. The extravasation of contrast material indicates a positive study finding. If the findings from the study are negative, the inferior mesenteric artery is cannulated, followed by the celiac artery. In some cases, aberrant vascular anatomy can contribute to colonic or small bowel circulation; in other cases, patients with upper GI bleeding (UGIB) may present in an uncommon clinical fashion.

Diverticula, angiodysplasia, and intestinal varices can be visualized by angiography. The characteristic angiographic findings of colonic angiodysplasias are clusters of small arteries during the arterial phase of the study, accumulation of contrast media in vascular tufts, early opacification, and persistent opacification due to the late emptying of the draining veins. If mesenteric angiography is performed at the time of active bleeding, extravasation of contrast media is visualized.

Once the bleeding point is identified, angiography offers potential treatment options, such as selective vasopressin drip and embolization. Thirteen publications reported experiences with selective mesenteric angiography. When 657 patients underwent mesenteric angiography, the percentage of positive study findings fluctuated between 27% and 86%, with an average of 45%. Because of the intermittent nature of LGIB, the number of positive study findings is significantly less with this invasive diagnostic modality.

Emergency angiography

Emergency angiography as an initial study is indicated in a highly selected group of patients with massive ongoing LGIB. Browder et al used 2 criteria to triage patients for emergency angiography^[37] : at least 4 units of blood transfusion in the first 2 hours following hospital admission and systolic blood pressure of less than 100 mm Hg with aggressive resuscitation. Fifty patients underwent emergency angiography, and bleeding was localized in 72% of patients. Vasopressin infusion was successful in 91%; however, 50% experienced bleeding following cessation of the vasopressin infusion.^[37] Thus, patients with ongoing hemorrhage, emergency angiography, and vasopressin infusion have improved operative morbidity, mortality, and outcome.

Widlus and Salis suggested that the use of Reteplase, a fibrinolytic agent, is safe and effective as a provocative agent in angiography. By stimulating bleeding to allow localization, in patients with occult, recurrent, massive LGIB.^[38] An initial diagnostic visceral arteriogram was performed and failed to identify the source of bleeding in each patient. When Reteplase was administered and provocative arteriography was repeated, bleeding was identified in 8 of 9 (89%) patients, and these patients were treated with microembolization, segmental resection, or conservatively.^[38]

Advantages and disadvantages of angiography

The advantages of angiography include: (1) This modality provides accurate localization of the bleeding; (2) it has a therapeutic utility that includes the use of vasopressin infusion or embolization; and (3) it does not require preparation of the bowel.

The disadvantages of angiography include: (1) It has a sensitivity of approximately 30-47%; (2) it can only be performed during active bleeding; and (3) it has a complication rate of about 9%. Such complications include thrombosis, embolization, and renal failure.^[25]

Also see Radiologic Approach to Lower Gastrointestinal Bleeding.

Double-contrast barium enema examinations can be justified only for elective evaluation of unexplained LGIB. Do not use barium enema examination in the acute hemorrhage phase, because it makes subsequent diagnostic evaluations, including angiography and colonoscopy, impossible.

Elective contrast radiography of the small bowel and/or enteroclysis is often valuable in investigation of long-term, unexplained LGIB (see Small Bowel Visualization ).

An esophagogastroduodenoscopy (EGD) is performed if a nasogastric (NG) tube aspirate is positive for blood, because about 10% of patients presenting with LGIB have bleeding originating from the upper GI tract. Small bowel endoscopic procedures are usually performed after EGD, colonoscopy, radionuclide scans, and angiography have been used and the bleeding site not localized.

Small bowel visualization includes the following modalities: (1) wireless capsule endoscopy (WCE), (2) push enteroscopy, (3) enteroclysis, and (4) double-balloon enteroscopy. Although no consensus exists on which modality to use initially, WCE is increasingly being used as the test of choice for small bowel bleeding.

Advantages and disadvantages of WCE

The advantages of WCE include: (1) it is noninvasive; (2) as opposed to push enteroscopy, WCE permits visualization of most or all of the small bowel; and (3) WCE identifies bleeding more often than push enteroscopy.^[39] Disadvantages of WCE include possible retention of the capsule in patients with severe motility disorders and Crohn disease with strictures, and no therapeutic capability is possible.

Contraindications to WCE include the following: (1) dementia (eg, patients not being able to cooperate with the swallowing of the capsule), (2) esophageal strictures, and (3) partial small bowel obstruction.

Push enteroscopy

Although WCE is used as the initial test for small bowel visualization, some experts recommend push enteroscopy as the initial test because of its therapeutic capability. Push enteroscopy is performed with a pediatric colonoscope or a dedicated enteroscope, and once the bleeding site is visualized, it can be treated or tattooed. The main disadvantage of push enteroscopy is that it generally reaches only the proximal 60 cm of the jejunum; bleeding sites beyond that cannot be detected.

Enteroclysis

Enteroclysis is a double-contrast study performed by passing a tube into the proximal small bowel and then injecting barium. Therefore, this evaluation is avoided in acute bleeding, because enteroclysis may compromise subsequent attempts at endoscopy and angiography. For the same reason, barium studies, such as air contrast barium enemas, are best avoided in acute LGIB.

Most colonic diverticula are false pulsion diverticula and are composed only of mucosa and submucosa herniated through the colonic wall musculature. Hemorrhage associated with diverticula comes from perforated vasa rectae located at the neck or the apex of the diverticula.

Colonic angiodysplasias are vascular ectasias commonly located on the right side of the colon. Microscopically, vascular ectasia consists of dilated thin-walled venules and capillaries localized in the submucosa of the colonic wall.