Blood in the stool: causes, symptoms, diagnosis, treatment: what's important to know

Blood in the stool is not a diagnosis in itself, but a symptom of bleeding in the gastrointestinal tract. The source may be in the anal canal, rectum, colon, small intestine, stomach, or even the esophagus. The presence of blood alone does not indicate the exact cause, but it always requires evaluation, as the same external symptom can conceal both benign anorectal problems and potentially dangerous conditions. [1]

Blood in stool can vary in appearance. Bright red blood often indicates a source in the rectum or anal canal. Dark red or maroon blood often suggests a higher source in the colon. Black, tarry stool, called melena, is usually associated with bleeding from the upper gastrointestinal tract. [2]

There is an important exception: very heavy bleeding from the upper gastrointestinal tract sometimes also manifests as bright red blood from the rectum. This is why the blood color alone cannot definitively determine the source. The doctor always compares the stool color with the person's overall condition, the duration of the symptom, pain, vomiting, hemoglobin levels, and other factors. [3]

Bleeding can be acute or chronic. Acute bleeding begins suddenly and can quickly lead to weakness, dizziness, fainting, and shock. Chronic bleeding can be minor, intermittent, and less noticeable, but over time it can cause iron deficiency anemia, fatigue, pallor, and shortness of breath. [4]

Even if bleeding is rare and seems "understandable," such as after constipation, this doesn't mean an examination isn't necessary. The American Society of Colorectal Surgeons specifically emphasizes that rectal bleeding should not be automatically attributed to hemorrhoids, especially if the symptom recurs, bowel habits change, abdominal pain, anemia, or weight loss develops. [5]

Table 1. How the appearance of blood helps to suggest the source

Type of stool or blood	What is more often assumed
Scarlet blood on paper or on the surface of the stool	Hemorrhoids, anal fissure, other anorectal source
Dark red or maroon blood mixed with stool	Source in the colon or distal small intestine
Black tarry stool	Upper gastrointestinal bleeding
Blood without visible pain after straining	Most often hemorrhoids, but not only
Intermittent bleeding and signs of anemia	Chronic hidden or barely noticeable bleeding

The table summarizes current understanding of the symptoms of gastrointestinal bleeding and anorectal bleeding. [6]

The main causes of blood in the stool

The most common and, at the same time, most misleading causes are hemorrhoids and anal fissures. Internal hemorrhoids are typically accompanied by small amounts of bright red blood on stool, paper, or in the toilet bowl after defecation, often without significant pain. Anal fissures, on the other hand, are more typically characterized by pain, burning, cramping, and a streak of blood on the surface of hard stool. Both conditions are common, but they should not be used as an explanation for every episode of bleeding without an examination. [7]

One of the most common causes of severe bleeding from the lower gastrointestinal tract in adults, and especially in the elderly, is diverticular disease. With diverticular bleeding, the bleeding often appears suddenly, can be quite profuse, and is not always accompanied by pain. In some patients, the bleeding stops on its own, but in others it recurs and requires endoscopic or radiological endovascular intervention. [8]

Another important cause is vascular lesions, primarily angiodysplasia and angioectasias. These are particularly significant in recurrent episodes of unexplained bleeding, in iron deficiency anemia, and in situations where colonoscopy reveals no obvious source in the colon. In the small intestine, vascular lesions are generally considered the leading cause of bleeding. [9]

Blood in the stool is common in inflammatory bowel disease and infectious colitis. These conditions typically involve blood along with diarrhea, urgency, abdominal pain, and sometimes fever, weight loss, and elevated inflammatory markers. In ulcerative colitis, blood in the stool can be one of the most noticeable symptoms even in the early stages of the disease. [10]

Polyps and colorectal cancer are particularly important to avoid. Blood in the stool can be the first noticeable symptom of a tumor, and not just in the elderly. The National Cancer Institute notes that in people under 50, four warning signs associated with early colorectal cancer include abdominal pain, rectal bleeding, diarrhea, and iron deficiency anemia. Rectal bleeding showed the strongest association with diagnosis. [11]

Finally, not all blood in the stool originates from the colon. Peptic ulcers of the stomach and duodenum, gastritis, mucosal tears following vomiting, esophageal varices, and other causes of upper bleeding can manifest as melena, and sometimes dark red or scarlet blood in cases of massive blood loss. It is especially important to remember the role of nonsteroidal anti-inflammatory drugs and blood thinners, which increase the risk of bleeding and can increase its severity. [12]

Table 2. Common causes and clinical clues

Cause	What is especially typical
Haemorrhoids	Bright red blood after a bowel movement, often without pain
Anal fissure	Pain during defecation, spasm, a little scarlet blood
Diverticular bleeding	Sudden, sometimes profuse, scarlet or burgundy blood
Inflammatory bowel disease	Blood along with diarrhea, pain, urgency, weight loss
Infectious colitis	Bloody stools accompanied by diarrhea, pain, and sometimes fever
Polyps and colorectal cancer	Recurring blood, anemia, stool changes, weight loss
Ulcerative bleeding	Black tarry stools, weakness, sometimes vomiting blood
Angiodysplasia and angioectasia	Recurrent bleeding, anemia, sometimes unclear source

The table is based on materials on gastrointestinal bleeding, hemorrhoids, inflammatory bowel disease and early signs of colorectal cancer.[13]

When urgent help is needed

The most dangerous situation is the combination of blood in the stool with signs of circulatory problems. These signs include fainting, severe weakness, clammy sweat, pallor, cold hands and feet, rapid pulse, confusion, shortness of breath, and severe dizziness. The National Institute of Diabetes and Digestive and Kidney Diseases (US) emphasizes that shock due to gastrointestinal bleeding is life-threatening and requires immediate treatment. [14]

Black, tarry stools also require urgent evaluation, especially if accompanied by coffee-ground vomiting, weakness, pre-syncope, or a drop in blood pressure. This is typical of upper gastrointestinal bleeding and is considered an emergency. Repeated passage of scarlet blood with clots is equally alarming. [15]

Not only massive bleeding but also recurring bleeding is considered dangerous. If blood appears repeatedly, if stool pattern and frequency change, if anemia, weight loss, nocturnal symptoms, or abdominal pain occur, an in-person examination by a doctor and often a colonoscopy are necessary. The "wait and see" approach often leads to a late diagnosis. [16]

A separate group consists of patients taking anticoagulants and antiplatelet agents. With these medications, even a seemingly minor bleeding episode requires a more careful assessment. However, current guidelines do not support independent discontinuation of medications, as the risk of bleeding is accompanied by the risk of thrombosis, heart attack, or stroke. [17]

Even if bleeding appears "typically hemorrhoidal," a doctor's visit is essential if the symptom persists after home treatment, if episodes recur, if the person is over 45 and has not been screened recently, or if there is a family history of colorectal cancer or inflammatory bowel disease. The presence of hemorrhoids does not rule out another, more serious condition. [18]

Table 3. When emergency care is needed and when a routine examination is needed

Situation	Tactics
Fainting, severe weakness, cold sweat, rapid pulse	Immediate emergency care
Black tarry stool	Same day urgent assessment
Multiple bright red or clotted blood	Same day urgent assessment
Blood while taking anticoagulants and antiplatelet agents	Urgent contact with a doctor, without unauthorized drug withdrawal
Recurring blood, anemia, weight loss, change in stool	A scheduled but quick in-person examination
Minor one-time bleeding after constipation	A medical evaluation is still needed, although the urgency may be lower.

The table summarizes the current criteria for suspicion of gastrointestinal bleeding. [19]

Diagnostics

Diagnosis begins with a detailed medical history and physical examination, rather than immediately with a comprehensive endoscopy. It is important to clarify the specific type of blood seen, whether it is associated with defecation, whether there is pain, constipation, diarrhea, fever, weight loss, anemia, use of nonsteroidal anti-inflammatory drugs, aspirin, or anticoagulants, and whether similar episodes have occurred in the past. If an anorectal source is suspected, a perianal examination, digital rectal examination, and, if possible, anoscopy are mandatory. [20]

Blood tests are usually performed initially. These include hemoglobin, platelets, coagulation parameters, kidney function, and sometimes blood type and Rh factor. If diarrhea is present, stool tests for infectious causes may be necessary. In cases of repeated episodes and suspected chronic blood loss, iron and ferritin levels are assessed. [21]

Colonoscopy remains the primary method for identifying the source in hemodynamically stable patients with suspected lower gastrointestinal bleeding. However, the modern approach differs from the old paradigm: performing colonoscopy within the first 24 hours in stable patients has shown no clear advantage over performing the procedure within 14 days. Therefore, the decision on urgency is not made "out of habit," but rather based on the severity of the condition and the likelihood of ongoing bleeding. [22]

If bleeding is significant and ongoing, especially in the presence of hemodynamic instability, computed tomography angiography plays a crucial role. It helps quickly localize the source and define the vascular anatomy for subsequent embolization. According to a review based on the updated guidelines of the American College of Gastroenterology, this method is particularly useful for significant lower bleeding. [23]

If the clinical picture strongly suggests an upper source, gastroscopy becomes the first line of defense. This is especially important in cases of melena, hematemesis, epigastric pain, use of nonsteroidal anti-inflammatory drugs, and signs of massive blood loss. With upper bleeding, gastroscopy not only identifies the cause but also allows for immediate hemostasis. [24]

If colonoscopy and gastroscopy fail to explain the bleeding and episodes continue, the physician considers a small intestinal source. In this situation, capsule endoscopy, enteroscopy, and other imaging techniques are used. Immune occult blood testing can be used to triage patients with symptoms of possible colorectal cancer in primary care, but it does not replace clinical evaluation and endoscopy for obvious blood in the stool or for significant red flags. [25]

Table 4. What diagnostic methods are needed and why?

Method	What is it used for?
Examination of the perianal area and digital examination	Search for fissures, hemorrhoids, rectal tumors, and other anorectal pathologies
Anoscopy	Clarification of the source in the anal canal and distal rectum
Complete blood count	Assessment of anemia and severity of blood loss
Coagulation and renal function tests	Risk assessment and preparation for interventions
Colonoscopy	The primary method when a lower source is suspected in a stable patient
Gastroscopy	The main method when an upper source is suspected
Computed tomography angiography	Rapid localization of active significant bleeding
Capsule endoscopy	Searching for a source in the small intestine in case of unclear bleeding

The table is based on current data on the diagnosis of gastrointestinal bleeding and recommendations for hemorrhoids and lower gastrointestinal bleeding. [26]

Treatment

Treatment depends not on the presence of blood in the stool itself, but on the cause and severity of the bleeding. In cases of significant blood loss, the first step is stabilization: venous access, fluid replacement, monitoring of vital signs, blood preparation if necessary, and rapid identification of the probable source. Regarding red blood cell transfusion, a restrictive strategy is now more commonly used: in hemodynamically stable patients without acute myocardial ischemia, a hemoglobin level below 7 g/dL is targeted, while in patients with cardiovascular disease, a higher threshold of approximately 8 g/dL is often considered. [27]

Endoscopic treatment plays a central role. During gastroscopy or colonoscopy, the physician can perform injection, thermal, or mechanical hemostasis. This not only confirms the diagnosis but also stops the bleeding without surgery. The National Institute of Diabetes and Digestive and Kidney Diseases (US) explicitly states that endoscopy and angiography are the primary treatment methods for gastrointestinal bleeding. [28]

For ongoing significant lower gastrointestinal bleeding after a positive computed tomography angiography (CT angiography), transarterial embolization is performed. According to a review based on the American College of Gastroenterology guidelines, performing embolization within 90 minutes of a positive angiography results in bleeding control in approximately 98% of cases, although the risk of complications and subsequent adverse outcomes remains. [29]

If hemorrhoids are the cause, dietary fiber, adequate fluid intake, and toilet habit modifications, particularly avoiding prolonged sitting on the toilet and straining, are considered first-line treatments. The American Society of Colorectal Surgeons notes that dietary and behavioral measures are the basis of treatment, while fiber reduces the risk of ongoing symptoms and bleeding. For anal fissures, stool softening and soaking are important, and for chronic fissures, topical calcium channel blockers are considered the preferred first-line treatment based on tolerability. [30]

If the source is located in the upper gastrointestinal tract and is associated, for example, with ulcerative bleeding, high-dose proton pump inhibitor therapy is used after successful endoscopic hemostasis. The European Society of Gastrointestinal Endoscopy, in its updated guidelines, recommends such therapy after endoscopic control of ulcerative bleeding to reduce the risk of recurrence. Further treatment depends on the cause, such as the need for Helicobacter pylori eradication or discontinuation of causative medications. [31]

A separate and very important issue is bleeding associated with anticoagulant and antiplatelet therapy. A joint guideline from the American College of Gastroenterology and the Canadian Gastroenterology Association does not support routine platelet transfusions in patients on antiplatelet therapy without severe thrombocytopenia and does not recommend automatically discontinuing aspirin if it is prescribed for secondary prevention of cardiovascular events. Therefore, self-discontinuing such medications when blood appears in the stool is a potentially dangerous mistake. [32]

Table 5. Treatment depending on the cause

Cause	What is usually the basis of treatment?
Haemorrhoids	Fibers, fluid, straining correction, local and minimally invasive therapy as indicated
Anal fissure	Stool softening, baths, local calcium channel blockers, and sometimes surgical treatment
Diverticular bleeding	Colonoscopic hemostasis; in case of active bleeding, angiography and embolization
Ulcerative bleeding	Gastroscopic hemostasis, proton pump inhibitors, treatment of the cause of the ulcer
Inflammatory bowel disease	Anti-inflammatory and immunomodulatory therapy based on a confirmed diagnosis
Infectious colitis	Treatment depends on the pathogen and severity
Angiodysplasia and angioectasia	Endoscopic treatment, sometimes drug therapy and repeated interventions
Bleeding associated with antithrombotic drugs	Individual correction under the supervision of a physician, without unauthorized cancellation

The table summarizes current approaches to treating the main causes of blood in the stool. [33]

Prevention, surveillance and screening

Prevention begins with reducing the likelihood of the most common benign causes of bleeding. For hemorrhoids and fissures, soft, regular stools, sufficient dietary fiber, normal fluid intake, and avoiding prolonged straining are key. While this isn't universal protection against all causes, it does work for the anorectal area. [34]

Medication review is also important. Nonsteroidal anti-inflammatory drugs (NSAIDs) increase the risk of gastrointestinal bleeding, while anticoagulants and antiplatelet agents can worsen existing bleeding. If such medications are needed for cardiovascular reasons, their adjustment should be made by a physician, not by the patient themselves. [35]

For asymptomatic adults at average risk for colorectal cancer, a separate preventive strategy is screening. The U.S. Preventive Services Task Force recommends screening for people aged 45–75 years, while for those aged 76–85 years, the decision is made on an individual basis, taking into account their health status and previous screenings. Screening options include colonoscopy and high-sensitivity stool tests. [36]

But it's important to distinguish between screening and diagnosis. Screening is intended for people without symptoms. If blood is already visible in the stool, it's not a matter of screening, but of diagnosing the cause. In such a situation, visible bleeding requires a clinical assessment, regardless of age, and even young age should not reassure either the patient or the physician. [37]

Monitoring after a bleeding episode depends on the cause. For some patients, relieving constipation and treating anorectal pathology is sufficient, while others require follow-up iron and hemoglobin tests. Still others require repeat endoscopy or long-term management for inflammatory bowel disease or vascular lesions. The most dangerous option is to assume the problem is resolved simply because the bleeding has temporarily stopped. [38]

Table 6. When colonoscopy is especially important

Situation	The role of colonoscopy
Recurring blood in the stool	Often shown to search for a source
Anemia and weight loss	Particularly important for excluding tumors and inflammation
Changing bowel habits	Often shown
No obvious anorectal source on examination	Shown more often
Bleeding persists after hemorrhoid treatment	Further search for the source is needed.
Asymptomatic person 45-75 years old with average risk	It is used as one of the screening options.

The table is based on guidelines for hemorrhoids, colorectal cancer, and lower bleed assessment.[39]

Frequently Asked Questions

If the blood is bright red, is it almost always hemorrhoids?
No. Bright red blood is indeed often associated with hemorrhoids and anal fissures, but it can also be caused by inflammatory bowel disease, rectal tumors, and other causes. Current guidelines explicitly warn that rectal bleeding should not be automatically attributed to hemorrhoids. [40]

Is there dangerous bleeding without pain?
Yes. For example, diverticular bleeding can be sudden and quite profuse without significant pain. Polyps and colorectal cancer also often bleed without pain. The absence of pain does not make the situation safe. [41]

What's more dangerous: scarlet blood or black stool?
Both can be serious. Black, tarry stools often indicate an upper source and require urgent evaluation. Scarlet blood can be a sign of a fissure, massive lower bleeding, or even severe upper bleeding. [42]

Is it possible to wait if there was only a small amount of bleeding and it was only a single event?
A small, one-time episode is indeed more often associated with a benign cause, but even in this situation, a face-to-face discussion with a doctor is advisable, especially if there is constipation, age over 45, anemia, a family history of colorectal cancer, or a recurrence of the symptom. If the episodes are repeated, waiting is no longer an option. [43]

Does every person with blood in their stool need a colonoscopy?
Not everyone, but many do. The decision depends on age, medical history, blood type, examination results, the presence of anemia, weight loss, and other red flags. If a clear anorectal source is not confirmed, the role of colonoscopy increases dramatically. [44]

If hemorrhoids are already present, can they be assumed to be the cause without further testing?
No. The presence of hemorrhoids does not rule out the possibility of another pathology. Attributing bleeding solely to hemorrhoids is considered one of the common reasons for delayed diagnosis of colorectal cancer. [45]

What should you do with aspirin or an anticoagulant if bleeding occurs?
Don't stop taking it on your own. Current guidelines require a simultaneous assessment of the risk of ongoing bleeding and the risk of thrombosis. For some medications and clinical situations, maintaining therapy is more important than immediate discontinuation. [46]

Can blood in the stool in young people also be a sign of cancer?
Yes, although benign causes are more common in young people. The US National Cancer Institute emphasizes that in people under 50, rectal bleeding is one of the main warning signs of early colorectal cancer and has the strongest association with diagnosis among the symptoms studied. [47]