Blood in your cat’s stool usually means something is irritating or inflaming the lower digestive tract. The causes range from minor (a sudden food change, a bout of stress) to serious (intestinal parasites, inflammatory bowel disease, or even cancer). The color and appearance of the blood tells you a lot about where the problem is coming from and how urgently your cat needs veterinary attention.
What the Blood Looks Like Matters
Bright red blood, whether streaked on the surface of the stool or mixed in with diarrhea, comes from the lower digestive tract: the colon, rectum, or anal area. This is the most common type cat owners notice, and it points to problems in the last stretch of the intestines.
Black, tarry stool is a different situation entirely. That pitch-black, asphalt-like color means blood has been digested on its way through the entire gastrointestinal tract, which places the bleeding source in the stomach or upper small intestine. Black stool signals significant blood loss and is more urgent than a streak of red. One caveat: certain medications containing bismuth (the active ingredient in Pepto-Bismol) can also turn stool very dark, so consider whether your cat has ingested anything unusual.
Colitis: The Most Common Culprit
Inflammation of the colon, called colitis, is the single most frequent reason cats pass blood in their stool. Colitis can be triggered by a surprising number of things. A sudden switch to a new food, eating something they shouldn’t have, or even a stressful event like a move, a new pet in the house, or a change in routine can inflame the colon enough to cause bleeding. In these cases, you’ll typically see soft stool or diarrhea with flecks or streaks of bright red blood, sometimes accompanied by mucus.
Stress-related colitis often resolves on its own within a day or two once the trigger passes. Dietary colitis tends to improve once you transition back to the original food or introduce new foods more gradually over a week to ten days. But if the bloody stool persists beyond a couple of days or your cat seems unwell, the problem likely goes deeper than a temporary upset.
Parasites and Infections
Intestinal parasites are a leading cause of bloody stool, especially in kittens, outdoor cats, and cats recently adopted from shelters. Roundworms, hookworms, coccidia, and giardia all irritate the intestinal lining enough to cause bleeding. Hookworms in particular latch onto the intestinal wall and feed on blood, which can produce both visible blood in the stool and anemia over time.
Bacterial infections can also inflame the gut and cause bloody diarrhea. Your vet will run a fecal exam to check for parasites and bacteria, so bringing a stool sample to the appointment saves time. Collect a piece about an inch long, place it in a clean sealed container or resealable bag, and bring it within six hours. If you can’t get to the vet that quickly, refrigerate the sample, but it loses accuracy after 24 hours even when chilled.
Inflammatory Bowel Disease
When bloody stool becomes a recurring pattern rather than a one-time event, inflammatory bowel disease (IBD) is one of the more common explanations. IBD is a chronic condition where immune cells infiltrate the walls of the intestines, causing persistent inflammation. Cats with IBD often show a cluster of symptoms: bloody stools, diarrhea, vomiting, weight loss, decreased appetite, and lethargy.
Inflammation concentrated in the colon is more likely to produce blood in the stool, while inflammation higher in the digestive tract tends to cause vomiting and weight loss instead. Diagnosing IBD typically requires blood work, ultrasound, and sometimes endoscopy or surgical biopsies, because intestinal lymphoma (a form of cancer) can look almost identical to IBD on imaging alone. Distinguishing the two is critical since the treatments and outlook differ significantly.
Anal Sac Problems
Cats have two small glands just inside the anus that normally release a small amount of fluid during defecation. When the ducts leading from these glands become swollen or blocked, the fluid thickens and can’t drain properly. Bacteria then multiply in the trapped material, turning it bloody. If the gland becomes abscessed and ruptures, you may notice bloody or sticky discharge on or near your cat’s stool, or draining from a small opening beside the rectum.
Cats with anal sac problems often scoot along the floor, lick excessively at their rear end, or strain during bowel movements. The blood from an anal gland issue tends to appear on the outside of the stool or on surfaces where the cat sits, rather than mixed throughout the feces.
Poisoning and Toxin Exposure
If your cat has access to areas where rodent poison is used, this is worth knowing about. Anticoagulant rat poisons work by blocking the body’s ability to clot blood. A cat that eats poisoned prey or directly ingests the bait can develop internal bleeding that shows up as blood in the stool, nosebleeds, pale gums, bruising, or blood in the urine. Another type of rodenticide containing vitamin D3 can cause vomiting blood and bloody diarrhea through a different mechanism, damaging organs by flooding the body with calcium.
Poisoning is a time-sensitive emergency. If you suspect your cat has been exposed to any rodenticide, don’t wait for symptoms to develop fully before seeking care.
How Your Cat’s Age Shapes the Cause
In kittens and young cats, parasites and infections top the list. Kittens pick up worms from their mother or from contaminated environments, and their immature immune systems make them more vulnerable to bacterial and protozoal infections. A kitten with bloody diarrhea, especially if lethargic or not eating, needs prompt veterinary attention because dehydration can become dangerous fast at that size.
In middle-aged and senior cats, the concern shifts toward chronic conditions like IBD and intestinal lymphoma. Older cats are also more prone to kidney disease, hyperthyroidism, and other systemic illnesses that can affect the gut indirectly. A senior cat with new-onset bloody stool warrants thorough diagnostic workup including blood panels, imaging, and potentially biopsies.
What Your Vet Will Do
A veterinary visit for bloody stool typically starts with questions about your cat’s diet, environment, stress levels, and how long the bleeding has been happening. After a physical exam, a fecal test is usually the first diagnostic step, checking for parasites and bacterial overgrowth. If that comes back clean, the next round of testing may include blood work to evaluate organ function, check for infections like feline leukemia, and rule out hyperthyroidism.
When initial tests don’t reveal a cause, imaging comes next. X-rays can identify blockages or obvious masses, while ultrasound gives a more detailed view of the intestinal walls and surrounding organs. In cases where IBD or cancer is suspected, endoscopy or exploratory surgery may be needed to collect tissue samples for biopsy. This progression from simple to complex testing is standard, so don’t be alarmed if your vet recommends multiple steps.
Signs That Signal an Emergency
A single streak of bright red blood on an otherwise normal stool, with a cat who is eating, drinking, and acting like themselves, is worth monitoring but not necessarily an emergency. The situation becomes urgent when you see any of the following alongside the bloody stool:
- Lethargy or collapse: your cat is weak, unresponsive, or unwilling to move
- Pale or white gums: a sign of significant blood loss or anemia
- Repeated vomiting: especially if the vomit also contains blood
- Large volumes of blood: stool that is mostly blood rather than having traces of it
- Black, tarry stool: indicating upper GI bleeding
- Not eating or drinking for more than 24 hours
- Known or suspected toxin exposure
Kittens under six months with bloody diarrhea should be seen quickly regardless of how they seem otherwise, because their small body size means they can deteriorate within hours from fluid loss alone.