The Canine Ledger

Blood in the Urine, Infections, and the Dog Who Strains but Can't Pee

A dog straining but passing little or no urine may be blocked, and that can kill. When blood in the urine can wait a day, what an infection is, and cranberry.

Written by thecanineledger

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If your dog keeps straining to pee but little or nothing comes out, or cries while trying: go to a vet now. This is especially urgent in male dogs, and in any dog who is also vomiting, weak or has a swollen, painful belly. A blocked bladder can kill within a short time.

The Merck Veterinary Manual’s owner page on urinary emergencies, reviewed in October 2026, is blunt about a blocked urethra: “A complete blockage can quickly cause dangerous changes in the blood and can lead to death if it is not treated promptly” (Merck, Urinary Emergencies in Dogs).

The danger is that it looks like something else. A dog squatting and straining in the garden looks, to most owners, like a dog who is constipated.

While many urinary problems in dogs can wait for an appointment, the dog who strains and produces nothing is the exception, and it is the one owners most often wait on. This page sets out how to tell the emergency from the problems that can wait for an appointment, what a urine infection is and isn’t, and what the evidence says about cranberry.

1. The emergency: straining with nothing coming out

What happens. Merck explains that “Most commonly, a urinary stone lodges in the urethra and blocks urine flow, especially in male dogs.” The urethra is the tube that carries urine out of the body. Tumours and blood clots can also block it. “Early on, the dog might strain and pass only drops of urine or a weak stream. Complete blockage causes toxins to build up and can lead to collapse or death. Complete obstruction is, therefore, an emergency.”

The signs Merck lists for a complete blockage:

  • “repeated straining to urinate without producing urine”
  • “frequent attempts to urinate with only a few drops or no urine”
  • “crying or other signs of pain while trying to urinate”
  • vomiting, weakness, loss of appetite, or a painful or swollen belly

Merck’s instruction: “A dog showing signs of complete urinary blockage needs emergency care right away.”

Is it pee or poo? Watch what your dog is doing. A dog straining to pee usually squats or lifts a leg in the position they use for urine, and you see drops or nothing. If you can’t tell, or you aren’t sure urine has come out in the last several hours, treat it as a possible blockage and phone.

Our note: The “is it pee or poo?” paragraph is our guidance. If your dog strains and passes no urine, treat it as an emergency.

→ Emergency Signs in Dogs: When to Go Now, Not Tomorrow

2. Blood in the urine

Blood in the urine looks alarming, and it always needs a vet. But on its own, in a dog who is otherwise well and passing urine normally, Merck’s owner pages don’t describe it as an emergency.

Common causes, from Merck’s owner pages:

CauseWhat else you might see
Bladder infection“frequent urination, painful urination, accidents in the house, and sometimes bloody urine”
Bladder stonesLarger stones can cause “pain, bloody urine, and difficulty urinating”
Tumours of the bladder or urethraMainly in older dogs. Merck notes they “often occur with urinary infections that don’t improve with antibiotics” (Merck, Tumors of the Urinary Tract in Dogs)
Prostate problems in entire malesMerck: “An infected or enlarged prostate can put pressure on the urethra, making urination difficult or painful”

When to go now rather than book an appointment: if there is blood with straining and little urine, if your dog is vomiting, weak, off food or in pain, or if the urine is very dark or there is a lot of blood. Otherwise, phone your vet the same day, and try to bring a fresh urine sample in a clean container.

Our note: We keep “go now” for blood with straining, other signs of illness, or heavy bleeding. Ask the clinic how to collect a sample.

An infection that keeps coming back is a reason to look further. Merck: “Dogs with repeated infections might need monitoring or more testing to look for urinary stones, tumors, cysts (pocket of fluids), birth defects, or other diseases.”

3. What a urine infection is, and isn’t

Female dogs are more likely to get them. Merck: “Female dogs are more likely than male dogs to get urinary infections.”

Bacteria in the urine are not always an infection. This surprises many owners. In a 2026 study of 533 dogs with no urinary signs at all, bacteria were found in the urine of 9.81% (Tallaksen et al., Journal of Veterinary Internal Medicine 2026). Vets call this subclinical bacteriuria.

A 2026 expert consensus on terms defines it as “The presence of bacteriuria, irrespective of the presence of pyuria or haematuria, in the absence of clinical signs of urinary tract disease potentially attributable to bacterial infection” (Weese et al., Journal of Small Animal Practice 2026). In plain terms: bacteria in the urine, with or without white cells or blood, in a dog who has no urinary signs.

Why this matters to you. If a routine urine test finds bacteria in a dog who seems fine, ask your vet whether treatment is really needed. Antibiotics have costs, and resistance is one of them.

Our note: We read only the abstract of the guideline on bacteria in the urine without signs, so we don’t say whether it should be treated.

→ Does Diarrhoea Need Antibiotics? What the Evidence Says

A urine culture is the test that names the bacteria. Merck: “To diagnose a bladder infection, your vet will usually collect a urine sample for analysis and bacterial culture.” A culture also shows which antibiotics will work.

Infections can climb. Merck warns that “untreated infections can spread to the kidneys”. Signs of a kidney infection include “pain near the kidneys, fever, vomiting, poor appetite, increased thirst, and increased urination.” A dog with urinary signs and fever or vomiting should be seen that day.

4. Cranberry

Cranberry supplements are widely sold for dogs’ bladders. A 2026 systematic review looked for every study of cranberry for preventing or treating urinary infection in dogs and cats (Weese & Weese, Journal of Veterinary Pharmacology and Therapeutics 2026).

It found three, with 106 dogs and 16 cats between them. “No studies reported statistically significant or numerical impacts of treatment.” The certainty of the evidence was “low to very low”.

Its conclusion: “current evidence is inadequate to properly assess the efficacy of cranberry supplementation.” That is not proof that cranberry doesn’t work. It is proof that nobody has shown it does in dogs.

Don’t use cranberry instead of a vet visit. A dog with urinary signs needs the urine tested, because the causes in the table above need different treatment.

Our note: We keep to what the review says about the evidence gap.

5. What we could not verify

Commonly saidWhat we found
“A dog straining is probably constipated”Not safe to assume. Merck lists repeated straining without producing urine as a sign of complete blockage, an emergency.
“Blood in the urine means an infection”Often, but not always. Stones, tumours and prostate problems can cause it too.
“Bacteria in the urine always need antibiotics”Not necessarily. About one in ten dogs with no urinary signs had bacteria in the urine in one 2026 study.
“Cranberry prevents bladder infections in dogs”Not shown. A 2026 systematic review found three small studies and no measurable effect.
“Only male dogs get blocked”Not only. Merck says blockage happens “especially in male dogs”, not only in males.

Sources

Always confirm with your vet before acting on anything on this page.