Blood in Cat Urine: Cystitis, Stones or Urethral Blockage

Blood in cat urine almost never arrives alone: something about the litter box has usually changed too. And urgency is decided not by the colour of the urine but by that — whether the cat can pass urine at all.

First Things First: A Male Cat That Cannot Urinate

The male feline urethra is long and narrow, and a plug of mucus, crystals and cells seals it shut. Urine stops leaving the body, the kidneys stop clearing potassium, and within a day or two the rising potassium disrupts the heart rhythm and kills the cat. This is not a wait-until-Monday problem. It is the nearest emergency clinic, tonight.

Owners mistake this blockage for constipation all the time, because from the outside it looks identical: the cat squats, strains, cries, produces nothing, walks away and squats again. The difference is what he is trying to pass. Check the litter: if no damp clump has appeared in 8–12 hours and the cat keeps straining, treat it as a urethral blockage until a vet says otherwise. Supporting signs are a tense, painful belly with a firm plum-sized or orange-sized bladder low down, insistent licking under the tail, vomiting, refusing food, and later lethargy and cold paws. What genuine constipation looks like is covered in constipation in cats.

In female cats the urethra is shorter and wider, so complete obstruction is uncommon. Blood in her urine still means the same lower urinary tract inflammation and deserves the same work-up.

What Blood in the Urine Actually Means

Blood enters urine wherever the lining is damaged — most often the bladder and urethra, less often the kidneys. Colour says little about severity: faintly pink urine can come from mild inflammation, while dark brown often means older bleeding that has already stopped. The behaviour around it is far more informative — repeated trips to the tray producing drops, crying while urinating, puddles outside the box, licking of the perineum.

It is also worth separating blood from its lookalikes. A reddish patch in the litter can come from beetroot in the diet, from a bleeding wound, or from the vulva of an unspayed queen in season. So "my cat is peeing blood" stays a hypothesis until urinalysis, not a diagnosis.

Feline Idiopathic Cystitis: The Commonest Cause

In cats under ten, most cases of blood in the urine turn out to be neither infection nor stones but idiopathic cystitis — inflammation of the bladder wall with no organism found. It is tightly linked to stress: a house move, a new pet, building work, an owner away, competition over the litter tray in a multi-cat home. The mechanism involves a damaged protective layer of the bladder lining and heightened pain signalling, which is why the cat goes often and passes very little.

Two practical consequences follow. First, antibiotics do not help, because there is no infection to treat. Second, an episode usually settles within five to seven days on its own but tends to come back, so prevention is built around water and environment — more wet food, more bowls, more trays, less competition between animals. What that means for the bowl is covered in choosing food for a cat.

Bladder Stones: Struvite Versus Oxalate

The second commonest cause is stones and sandy crystal debris. The two main types behave in opposite ways. Struvite forms in alkaline urine and can be dissolved on a therapeutic diet. Calcium oxalate does not dissolve at all and has to be removed physically. That is why "a urinary food" without knowing the stone type is risky: a diet that dissolves struvite can make oxalate management worse. The difference and what diet genuinely changes is set out in feeding a cat with urinary stones, and when a prescription diet is justified at all in therapeutic pet food.

Stones and crystals are also what most often produce the blockage in male cats: fine crystals bound with mucus form the plug itself.

Urinary Infection: Rare in Young Cats

Bacterial cystitis is the familiar explanation in humans, but in cats under ten it is uncommon. Infection becomes plausible when there is a background: chronic kidney disease, diabetes, age over ten, recent catheterisation. In an older cat with blood in the urine it is worth looking wider straight away — kidneys and metabolism. If she has also started drinking much more, that strongly favours a systemic cause: see cat drinking a lot and feeding a cat with kidney disease.

When to See a Vet Urgently

Tonight, without waiting for morning:

• a male cat strains and produces no urine — no damp clumps for more than eight hours;
• crying or groaning while urinating, refusing to leave the tray (telling pain vocalising from ordinary demands is covered in cat meowing constantly);
• a tense abdomen the cat will not let you touch;
• vomiting and refusing food and water alongside litter box trouble — that combination is discussed in vomiting and diarrhoea in cats;
• lethargy, an unsteady gait, cold paws, hiding and not responding — see lethargic cat;
• urine the colour of strong tea, or visible clots.

Within a day or two if the cat eats, is active and passes normal volumes, but the urine looks pink or the trips to the tray have become noticeably more frequent.

What Not to Do at Home

• Do not give human medicines. Human painkillers and anti-inflammatories are lethal to cats; any medication comes only on a veterinarian's prescription.
• Do not massage or press on the abdomen of a cat suspected of being blocked: an overfull bladder can rupture.
• Do not restrict water to make the cat go less often — that is the opposite of what is needed.
• Do not start a therapeutic urinary diet blindly, before the stone type is known.
• Do not wait it out once appetite has dropped: refusing food is dangerous in itself — why a cat is not eating.

What Tests and Scans Will Clarify It

The baseline set is short and usually enough:

• Urinalysis with sediment microscopy — red and white cells, pH, specific gravity, crystals. This is the only way to separate cystitis from stones and from infection.
• Urine culture — when the sediment and the cat's age make infection plausible.
• Biochemistry and a complete blood count — urea, creatinine and especially potassium in a blocked cat; the values are explained in cat blood test.
• Ultrasound of the bladder and kidneys — shows sand, stones and wall thickening: cat abdominal ultrasound.
• Radiographs — many stones are radiopaque and count well on a film: cat X-ray.

A lab report or ultrasound conclusion can be uploaded to pet results interpretation, and an imaging report to pet imaging interpretation: the service explains what the numbers and phrasing mean against feline reference ranges. If there is no report yet and all you have is behaviour and the litter tray, start by describing the symptoms. Other common complaints are collected on the cat symptoms page.

This article is informational. Diagnosis and treatment of your pet are the job of a veterinarian.