What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Melena: Blood in Stool in Pets

Name: Melena: Blood in Stool in Pets
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Melena is black, tarry, foul-smelling stool produced when blood is digested in the upper gastrointestinal tract before it is passed. It is a sign, not a diagnosis, and it always means the same thing in practical terms: your pet is bleeding somewhere in the stomach or the upper small intestine, and the blood has been exposed to stomach acid and intestinal enzymes long enough to turn black. Melena blood in stool is different from hematochezia, which is fresh red blood from the lower bowel, and it is different from dark stool caused by diet, iron supplements, or certain drugs.

Owner-facing triage summary. Melena is a medical problem, not a grooming or food problem. A single black tarry stool in an otherwise bright, eating, drinking pet still warrants a veterinary call the same day. Melena combined with any of the following is an emergency: pale gums, weakness or collapse, vomiting blood, a distended or painful abdomen, a heart rate that feels fast or weak, known ingestion of a human painkiller such as ibuprofen, naproxen, or a prescription NSAID, or a puppy or kitten with vomiting and diarrhea. Do not wait for a second stool to confirm the color. Do not give human antacids, human ulcer drugs, or human pain relievers while you wait.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

At a Glance: Melena Versus Hematochezia Versus Dark Diet Stool

The single most useful thing an owner can do is look carefully at the stool and describe it accurately. The table below separates the three situations that owners most often confuse.

Feature	Melena	Hematochezia	Dark stool from diet or iron
Color	Black, tarry, like coffee grounds or tar	Bright red, fresh	Dark brown, sometimes nearly black
Texture	Sticky, gelatinous, often soft or liquid	Variable, blood often coats or streaks the stool	Normal to firm, formed
Smell	Strong, foul, digested blood odor	Normal fecal odor or mildly altered	Normal fecal odor
Source	Upper GI tract, usually stomach or upper small intestine	Lower GI tract, colon, rectum, or anus	No bleeding, pigment or mineral effect
Typical triggers	Ulcer, NSAID or steroid injury, coagulopathy, foreign body, parvovirus, hookworms, mass	Colitis, polyp, rectal mass, anal gland disease, parvovirus in some cases	High-iron diet, blood-based treats, iron tablets, bismuth, activated charcoal
Owner action	Call a veterinarian the same day	Call a veterinarian the same day	Confirm diet and supplements, then call if unsure

Two details matter. First, melena is not always uniformly black. It can range from dark coffee-ground material to true black tar, and the tarry texture is the more reliable clue than the shade alone. Second, diet-related dark stool is usually formed and normal-smelling, while melena is typically soft, sticky, and foul. If you cannot tell the difference, treat it as melena until a veterinarian says otherwise.

What Melena Actually Is: Anatomy and Physiology

Blood that enters the upper gastrointestinal tract is broken down by stomach acid, pancreatic enzymes, and intestinal bacteria. Hemoglobin is converted into hematin and other pigments that are black. That is why the stool turns black rather than red. The upper tract includes the esophagus, stomach, and the first part of the small intestine, the duodenum and jejunum. Bleeding from these regions tends to produce melena because the blood has time to be digested before it reaches the colon.

Bleeding from the colon, rectum, or anus usually produces hematochezia, because the blood passes through too quickly to be digested. A dog or cat can have both at once, and a pet with a bleeding mass high in the bowel plus colitis lower down may pass stool with black and red components. The presence of both does not change the urgency, it just widens the list of possible sources.

Melena also implies a certain volume of blood loss. Small amounts of blood from the upper tract may be invisible to the eye and are called occult bleeding. Melena becomes visible when enough blood has been digested to darken the stool. In cats, a controlled study of fecal occult blood testing showed that melena was only visible at higher doses of administered blood, while the fecal occult blood test turned positive at much lower doses [1]. That study used an animal protein-free diet and measured hemoglobin dosed by body weight. The practical takeaway is that visible melena represents a meaningful bleed, and a negative fecal occult blood test does not fully rule out small ongoing losses.

Causes of Melena in Dogs and Cats

Melena has a long differential list. The goal of the workup is not to guess, but to move through the list in a logical order based on history, examination, and basic testing.

Gastrointestinal ulceration

Ulcers in the stomach or duodenum are among the most common causes of melena in small animal practice. Ulcers can be caused by drugs, by systemic illness, by stress in a hospitalized patient, or by a mass that has eroded through the mucosa. A gastric leiomyoma, a benign smooth muscle tumor, has been reported to cause melena and abdominal pain when it ulcerates [2]. In dogs, a neuroendocrine carcinoma at the gallbladder neck caused acute melena and hematemesis, and the bleeding only stopped after the mass was removed [3]. A gastric carcinoma in the chow chow breed is associated with vomiting, loss of appetite, diarrhea, and melena, and most affected dogs in that report were euthanized within two weeks of diagnosis [4]. These cases share a pattern: an ulcerated mass bleeds into the upper tract, and the bleeding does not respond to gastroprotectants alone.

NSAID and steroid use

Nonsteroidal anti-inflammatory drugs are a leading cause of gastrointestinal ulceration and bleeding in dogs. A report of four dogs that ingested lornoxicam, a human NSAID not approved for canine use, described melena, anorexia, and depression appearing one to four days after ingestion [5]. Three of those dogs had also received low doses of prednisolone close in time to the NSAID. Major findings included mucosal pallor, severe anemia, neutrophilic leukocytosis, and panhypoproteinemia, and three dogs had perforated pyloric and duodenal ulcers confirmed at surgery or postmortem. Three of the four dogs survived to discharge after prolonged hospitalization, supportive care, and multiple transfusions. The combination of an NSAID and a steroid is a well-recognized risk multiplier, and owners should never give a human NSAID to a pet.

Coagulopathy

Any disorder that impairs clotting can produce melena. This includes rodenticide poisoning, liver failure, disseminated intravascular coagulation, and inherited clotting factor deficiencies. A juvenile dog with a jejunal arteriovenous malformation and multiple acquired extrahepatic portosystemic shunts presented with a one-month history of persistent melena and severe anemia [6]. The malformation was removed surgically, but the dog later developed hepatic encephalopathy and was euthanized fifteen months after surgery. That case shows how abnormal vasculature and abnormal portal blood flow can combine to cause chronic gastrointestinal bleeding.

Foreign body and linear foreign body

A foreign body that lodges in the stomach or small intestine can erode the mucosa and bleed. An 8-year-old Beagle with a history of recurrent ingestion of cotton-based toy fragments presented with anorexia, abdominal pain, intermittent vomiting, and melena, and was found to have an intestinal osteosarcoma at surgery [7]. That case is unusual because the mass was a tumor, but the history of repeated foreign material ingestion is a common thread in dogs that present with chronic intermittent melena.

Parvovirus

Canine parvoviral enteritis damages the intestinal crypts and can cause bloody diarrhea. In a large retrospective study of 322 dogs with parvoviral enteritis, 91 percent survived with in-hospital treatment and a median hospitalization of 79 hours [8]. Low blood glucose, high total magnesium, and a low hematocrit at presentation were associated with lower odds of survival. Melena can occur in parvovirus because the virus damages the small intestine, and any puppy with vomiting, diarrhea, and black or bloody stool should be seen immediately.

Hookworms and other parasites

Hookworms attach to the small intestinal mucosa and feed on blood. Heavy infestations can cause melena and anemia, especially in puppies and kittens. The Companion Animal Parasite Council recommends year-round parasite prevention and periodic fecal testing for pets, and that guidance applies directly here. A fecal flotation and a fecal antigen test are part of the standard workup for melena in a young animal or any animal with a history of scavenging or incomplete prevention.

Neoplasia

Tumors of the stomach, small intestine, and adjacent organs can bleed. A feline primary duodenal carcinoid caused recurrent hematemesis and melena in a 15-year-old Persian cat, and the bleeding could not be controlled despite partial resection and cauterization, and the cat died of severe anemia [9]. A primary colonic hemangiosarcoma in a 13-year-old miniature dachshund caused hematochezia, melena, and weight loss [10]. A primary mesenteric root osteosarcoma in a 10-year-old boxer mix caused hematochezia, melena, and dyschezia, and the dog was euthanized because the mass was not resectable [11]. A cervical intravascular osteosarcoma in a 10.5-year-old standard poodle caused severe anemia and melena before euthanasia [12]. These reports illustrate that neoplasia can cause melena from many locations, not only from the stomach.

Hypoadrenocorticism

Hypoadrenocorticism, or Addison's disease, can present with chronic gastrointestinal signs and gastrointestinal blood loss. A multicenter study of 151 dogs with chronic gastrointestinal disease found hypoadrenocorticism in 6 dogs, a prevalence of 4 percent, and 4 of those 6 dogs had melena or hematochezia [13]. A separate case report described a 3-year-old Rottweiler with hypoadrenocorticism that developed severe acute anemia from gastrointestinal hemorrhage and required a blood transfusion when the hematocrit fell to 9 percent [14]. Hypoadrenocorticism is a treatable cause of melena that is easy to miss if the veterinarian does not consider it.

Uncommon causes

A dog envenomated by multiple paper wasps developed vomiting, melena, and anuria, with anemia, severe azotemia, hyperbilirubinemia, and markedly elevated creatine kinase, and died 48 hours after presentation despite treatment [15]. Canine tuberculosis is rare in the United States, and in a review of five cases in Brazil, melena was reported in all dogs with clinical signs [16]. These causes are uncommon, but they show why a full history, including travel, exposure, and recent events, matters.

Differential Table by Species: Dog Versus Cat

The same sign has a different probability distribution in dogs and cats. This table organizes the main differentials by species.

Cause	Dogs	Cats
NSAID or steroid-associated ulcer	Common, especially with human NSAIDs or combined NSAID and steroid use [5]	Less commonly reported but still a risk with any NSAID or steroid
Gastric or duodenal ulcer	Common	Common
Parvovirus	Common in unvaccinated puppies and young dogs [8]	Not a canine parvovirus disease, feline panleukopenia is the analogous viral enteritis
Hookworms	Common in puppies and dogs with incomplete prevention	Hookworms occur but are less common than in dogs
Foreign body	Common, especially in young dogs with pica [7]	Common, especially linear foreign bodies such as string or tinsel
Gastrointestinal neoplasia	Gastric carcinoma in chow chows [4], intestinal osteosarcoma [7], colonic hemangiosarcoma [10], mesenteric osteosarcoma [11]	Duodenal carcinoid [9], lymphoma, adenocarcinoma
Coagulopathy	Rodenticide, liver failure, DIC	Rodenticide, liver failure, DIC
Hypoadrenocorticism	Recognized cause of chronic GI signs with melena [13] [14]	Rare
Vascular malformation	Jejunal arteriovenous malformation reported in a juvenile dog [6]	Rare
Gallbladder or biliary neoplasia	Neuroendocrine carcinoma reported [3]	Rare

Cats hide gastrointestinal disease until it is advanced. A cat with a bleeding duodenal carcinoid may eat normally and behave normally until the anemia is severe [9]. Weight loss, subtle vomiting, and a change in grooming or hiding behavior are often the only early clues. Owners should weigh cats monthly at home if possible, because a slow downward trend is easier to detect than a single low weight at the clinic.

Risk Factors

Several factors raise the probability that melena is caused by a specific problem.

Age. Puppies and kittens are at higher risk for parvovirus, hookworms, and foreign bodies. Middle-aged and older pets are at higher risk for neoplasia and for chronic kidney or liver disease that alters drug handling.
Breed. Chow chows have an increased risk of gastric carcinoma [4]. Belgian Tervurens also have a recognized increased risk. Any breed can develop ulcers or foreign bodies.
Medications. Any NSAID, especially a human NSAID such as ibuprofen, naproxen, or lornoxicam, raises the risk of ulceration and bleeding [5]. Corticosteroids raise the risk further, particularly when combined with an NSAID.
Parasite prevention. Pets without year-round prevention are at higher risk for hookworm-associated bleeding.
Diet and chewing behavior. Dogs that chew and swallow toys, string, or fabric are at higher risk for foreign body obstruction and mucosal injury [7].
Vaccination status. Unvaccinated puppies are at high risk for parvovirus [8].
Chronic illness. Liver disease, kidney disease, and hypoadrenocorticism can all predispose to gastrointestinal bleeding [13] [14].

How Veterinarians Evaluate Melena

The workup for melena is systematic. The veterinarian starts with a full history and physical examination, then uses testing to narrow the source and the cause.

History

The history should cover the color, consistency, and frequency of the stool, the duration of the problem, any vomiting or hematemesis, appetite and water intake, weight change, energy level, and any known ingestion of drugs, toys, garbage, or rodenticide. Ask specifically about human medications. Owners often do not think of a single ibuprofen tablet as a drug exposure, but it can cause severe ulceration [5].

Physical examination

The veterinarian will check mucous membrane color, capillary refill time, heart rate, pulse quality, hydration, abdominal palpation, and rectal examination. Pallor suggests anemia. A painful or distended abdomen suggests ulceration, obstruction, or peritonitis. A rectal examination can detect a mass, melena coating the rectal mucosa, or hematochezia.

Laboratory testing

A complete blood count, serum biochemistry profile, and urinalysis are standard. The blood count shows whether the anemia is regenerative or non-regenerative and whether there is an inflammatory leukogram. The biochemistry profile assesses liver and kidney function, electrolytes, glucose, and total protein. A low glucose, high magnesium, or low hematocrit at presentation is associated with lower survival in parvoviral enteritis [8]. Coagulation testing is indicated if bleeding is suspected to be due to a clotting disorder.

The plasma urea-to-creatinine ratio has been proposed as a non-invasive marker of upper gastrointestinal bleeding. In a prospective study of 95 anemic dogs, the ratio was not significantly different between dogs with overt gastrointestinal bleeding, occult gastrointestinal bleeding, and anemia of other cause [17]. That means the ratio should not be used alone to make or exclude the diagnosis. It can still be part of the overall picture, but it does not replace imaging or endoscopy.

Fecal testing

Fecal flotation and fecal antigen testing for hookworms and other parasites are part of the standard workup. Fecal occult blood testing has good analytical sensitivity in cats, with positive results at doses as low as 1.5 mg/kg of hemoglobin in one cat and in all cats at 15 mg/kg or higher [1]. The test is a screening tool, not a substitute for imaging or endoscopy.

Imaging

Abdominal radiographs can show a foreign body, an obstruction, or a mass. Abdominal ultrasound is often more useful because it can show wall thickening, masses, ulcers, free fluid, and vascular abnormalities. In the gallbladder carcinoma case, ultrasound showed signs of an early mucocele and the mass was only found at surgery [3]. In the duodenal carcinoid case, ultrasound and CT showed a mass in the proximal descending duodenum [9].

Endoscopy and surgery

Gastroduodenoscopy allows direct visualization of the stomach and duodenum and can identify ulcers, masses, and areas of active bleeding. It also allows biopsy. In the gallbladder carcinoma case, gastroduodenoscopy was unremarkable, and the diagnosis required exploratory laparotomy [3]. That is an important lesson: a normal endoscopy does not rule out a bleeding source outside the stomach or duodenum. Exploratory surgery is sometimes necessary for diagnosis and treatment.

Decision Flowchart for Upper Versus Lower GI Bleeding

The flowchart below walks through the first decisions a veterinarian makes when a pet presents with blood in the stool.

flowchart TD
    A[Blood in stool] --> B{Stool black and tarry}
    B -->|Yes| C[Melena upper GI source]
    B -->|No| D{Stool bright red}
    D -->|Yes| E[Hematochezia lower GI source]
    D -->|No| F[Dark stool from diet or drug]
    C --> G[Check perfusion and anemia]
    E --> H[Check for mass or colitis]
    G --> I{Unstable or pale}
    H --> I
    I -->|Yes| J[Emergency stabilization]
    I -->|No| K[Staged diagnostic workup]
    J --> L[Transfusion and source control]
    K --> M[Imaging and endoscopy]

Evidence-Based Management

Management depends on the cause, but the general principles are the same: stabilize the patient, stop the bleeding, treat the underlying cause, and monitor for recurrence.

Stabilization

A pet with melena and signs of shock needs intravenous fluids, oxygen if needed, and possibly a blood transfusion. The decision to transfuse is based on the degree of anemia, the rate of ongoing blood loss, and the clinical status of the patient. In human medicine, a restrictive transfusion strategy targeting a hemoglobin threshold of 7 g per deciliter improved survival and reduced further bleeding compared with a liberal strategy targeting 9 g per deciliter in patients with severe acute upper gastrointestinal bleeding [18]. That trial was in people, not pets, so the exact threshold does not transfer directly. The principle does transfer: transfuse for clinical need, not for a number alone.

Source control

If the bleeding is from an ulcer, medical management with a proton pump inhibitor and removal of the offending drug is often enough. If the bleeding is from a mass, surgery is usually required. The gallbladder carcinoma case was cured by cholecystectomy, and the dog remained free of clinical signs 13 months later [3]. The jejunal arteriovenous malformation was removed by enterectomy, and the dog improved initially [6]. The duodenal carcinoid could not be controlled surgically, and the cat died of severe anemia [9]. Source control is the single most important determinant of outcome when a structural lesion is bleeding.

Gastroprotectants

Proton pump inhibitors are commonly used in pets with gastrointestinal ulceration. A randomized placebo-controlled trial of prophylactic omeprazole in dogs undergoing surgery for acute thoracolumbar intervertebral disc extrusion found that omeprazole did not decrease the frequency of gastrointestinal complications compared with placebo [19]. Gastrointestinal signs developed in 50 percent of the omeprazole group and 41 percent of the placebo group, and melena was not observed in either group. That trial was about prophylaxis in a specific surgical population, not about treatment of active ulceration, so it does not mean omeprazole is useless for a bleeding ulcer. It does mean that prophylactic acid suppression is not a guaranteed protection against gastrointestinal signs.

Deworming

If hookworms or other blood-feeding parasites are found, appropriate deworming is part of treatment. The Companion Animal Parasite Council recommends year-round prevention and follow-up fecal testing after treatment to confirm clearance.

Treating the underlying disease

Hypoadrenocorticism is treated with mineralocorticoid and glucocorticoid replacement, and the gastrointestinal bleeding resolves with treatment of the underlying disease [13] [14]. Coagulopathy is treated with vitamin K, plasma, or specific factor replacement depending on the cause. Parvovirus is treated with supportive care, antiemetics, fluids, and antibiotics for secondary bacterial translocation, and most dogs survive with in-hospital treatment [8].

Follow-up and recheck timing

The recheck schedule depends on the cause. A pet treated for an ulcer is usually rechecked in one to two weeks to confirm that melena has resolved and that the hematocrit is stable. A pet treated for parasites is rechecked with a fecal test after treatment. A pet that had surgery for a mass is rechecked according to the surgeon's plan, often at two weeks for the incision and then at longer intervals for staging. A pet with hypoadrenocorticism is rechecked with electrolytes and an ACTH stimulation test to confirm the dose is correct.

Unsafe Home Remedies

Several common home remedies are dangerous in a pet with melena.

Human NSAIDs. Ibuprofen, naproxen, aspirin, and lornoxicam can cause severe ulceration and perforation [5]. Never give these to a pet.
Human antacids and acid suppressants. These are not dosed for pets, and they can mask signs without treating the cause. Do not give them without veterinary direction.
Withholding food and water. A pet with melena may be dehydrated and anemic. Withholding water worsens perfusion. Follow veterinary instructions.
Waiting to see if it resolves. Melena can be the first sign of a life-threatening bleed. Waiting allows the anemia to worsen.
Giving iron supplements. Iron can darken the stool further and does not treat the bleeding source.

Prevention

Prevention focuses on the causes that are avoidable.

Keep all human medications out of reach. Store ibuprofen, naproxen, aspirin, and prescription NSAIDs in closed cabinets. Never give a human painkiller to a pet.
Use pet-specific NSAIDs only under veterinary supervision. Do not combine an NSAID with a steroid unless the veterinarian specifically directs it.
Keep parasite prevention current. Follow the Companion Animal Parasite Council recommendations for year-round prevention and periodic fecal testing.
Vaccinate puppies and kittens on schedule. Parvovirus is preventable with vaccination, and unvaccinated puppies are at highest risk [8].
Manage chewing and pica. Keep toys, string, and fabric out of reach for dogs that swallow foreign material [7].
Monitor older pets for subtle signs. Weight loss, reduced appetite, and intermittent vomiting can precede a bleeding mass. Early evaluation is easier than emergency treatment.

Prognosis

Prognosis depends on the cause and how quickly treatment starts. Dogs with parvoviral enteritis have a good prognosis overall, with 91 percent survival in one large study [8]. Dogs with NSAID-induced perforated ulcers can survive with aggressive care, but the morbidity is high and multiple transfusions may be needed [5]. Dogs with hypoadrenocorticism can do well once the underlying disease is treated [13] [14]. Dogs with gastric carcinoma in the chow chow breed often have a poor prognosis, with most euthanized within two weeks of diagnosis in one report, although two dogs treated aggressively survived 12 and 36 months [4]. Cats with duodenal carcinoid may have a poor prognosis if the bleeding cannot be controlled [9]. The common thread is that early recognition and source control improve the odds.

Limitations and When to Contact a Veterinarian

Individual cases vary, and only a veterinarian who examines your pet can determine the cause and the right treatment. Contact a veterinarian immediately if any of the following apply:

Black tarry stool, especially if it is new or recurrent
Pale gums, weakness, collapse, or difficulty breathing
Vomiting blood or material that looks like coffee grounds
A distended, painful, or rigid abdomen
Known or suspected ingestion of a human NSAID, rodenticide, or other toxin
A puppy or kitten with vomiting, diarrhea, and lethargy
A cat that has stopped eating, is hiding more, or is losing weight
Melena that persists after treatment or recurs after it resolves

If you are unsure whether the stool is melena or diet-related dark stool, call your veterinarian and describe the color, texture, and smell. A photograph of the stool can help.

Frequently Asked Questions

Is melena always a sign of a serious problem?

Melena always means blood has been digested in the upper gastrointestinal tract, so it always deserves veterinary attention. The cause may be as treatable as a hookworm infection or as serious as a bleeding tumor, and only testing can tell the difference.

How can I tell melena from dark stool caused by diet?

Melena is black, tarry, sticky, and foul-smelling, while diet-related dark stool is usually formed and has a normal fecal odor. If you cannot tell, treat it as melena and call your veterinarian.

Can I give my pet an antacid while I wait for the appointment?

No. Human antacids and acid suppressants are not dosed for pets and can mask signs without treating the cause. Do not give any medication without veterinary direction.

What is the difference between melena and hematochezia?

Melena is digested blood from the upper gastrointestinal tract and appears black and tarry. Hematochezia is fresh red blood from the lower gastrointestinal tract and usually coats or streaks the stool.

Do cats get melena?

Yes. Cats can develop melena from ulcers, tumors, coagulopathy, and other causes. Cats often hide gastrointestinal disease until it is advanced, so weight loss and subtle behavior changes matter.

Is melena in puppies an emergency?

Yes. Melena in a puppy can be caused by parvovirus, hookworms, or a foreign body, and puppies can deteriorate quickly. Call an emergency veterinary hospital right away.

Can melena go away on its own?

Sometimes the bleeding stops on its own, but the underlying cause does not. Melena that resolves without treatment can recur, and the anemia may persist. A veterinarian should still evaluate your pet.

What tests will my veterinarian run for melena?

Expect a physical examination, blood count, biochemistry profile, fecal testing, and imaging such as radiographs or ultrasound. Endoscopy or exploratory surgery may be needed if the source is not found with less invasive tests.