Causes of atraumatic bleeding in dogs: key facts and guidance

Atraumatic bleeding in dogs refers to bleeding that occurs without an obvious injury or trauma, such as blood appearing from natural orifices including the ears, rectum, urinary tract, mouth, or reproductive organs. This type of bleeding is a symptom that should never be ignored, as it often signals underlying health issues requiring prompt veterinary attention.

In this comprehensive article, we explore the common areas where atraumatic bleeding may occur in dogs, uncover the typical causes, and explain why early diagnosis and treatment are essential to protect your pet's wellbeing.

Common sites of atraumatic bleeding in dogs

Any of a dog's natural orifices can bleed without external trauma if an internal problem arises. Common sites include:

• The ears
• The rectum
• The vulva or penis
• The mouth
• The bladder or urinary system

Bleeding from the ears

One prevalent cause of atraumatic ear bleeding is an infestation of ear mites, which are tiny parasites that cause intense itching and irritation. As your dog persistently scratches or shakes its head, this can lead to cuts, lesions, or even small abscesses inside or around the ear canal, resulting in bleeding. Veterinary examination and appropriate treatment are necessary to eliminate ear mites and manage any secondary infections.

Rectal bleeding

Rectal bleeding can result from issues affecting the anus and lower digestive tract. Causes range from inflamed anal glands and rectal polyps to more serious internal bowel problems.

Bright red blood or pus-like discharge often points to issues near the anus, such as infections or inflammation. Conversely, dark brown or black blood typically suggests bleeding higher up in the digestive tract and warrants urgent veterinary evaluation to rule out ulcers, tumours, or other serious diseases.

Blood in the urine

When blood appears in your dog’s urine—sometimes visible as red streaks or causing orange discoloration—it is usually a sign of urinary tract inflammation or infection, such as cystitis or kidney disease. Other causes include bladder or kidney stones and crystals, which can irritate and damage the delicate urinary lining, leading to bleeding.

Any sign of blood in the urine should be assessed promptly by your vet, who may perform urine testing, imaging, or other diagnostics to find the cause and recommend appropriate treatment.

Bleeding from the penis

Penile bleeding can be indicative of reproductive system problems, often linked to the testes or prostate gland. Prostate disease is a common cause, especially in entire (unneutered) male dogs. Other causes may be internal injuries or sexually transmitted infections.

Your vet will conduct a thorough examination and may suggest blood tests, ultrasound, or other investigations to identify the underlying cause and provide targeted care.

Bleeding from the vulva

In unspayed female dogs of breeding age, bleeding from the vulva is generally linked to the heat (oestrus) cycle, which occurs twice yearly. This natural bleeding is accompanied by behavioural changes and physical signs such as swelling.

If bleeding occurs outside of the expected heat cycle, it may indicate health issues such as pyometra, a dangerous infection of the uterus. In open pyometra, discharge containing blood or pus can be seen, and this condition requires emergency veterinary treatment to avoid life-threatening complications.

Oral bleeding

Bleeding from the mouth or gums that is not caused by recent trauma or eating something abrasive often points to dental disease. Common issues include gum inflammation (gingivitis), dental abscesses, loose or damaged teeth, and sometimes benign or malignant growths within the mouth.

A full dental examination by your vet is essential. They may recommend professional dental cleaning under anaesthesia and treatment for any infections or tumours detected.

Underlying causes of atraumatic bleeding in dogs

Beyond the visible sites of bleeding, atraumatic haemorrhage may arise from several serious internal conditions:

• Internal tumours: Aggressive cancers like hemangiosarcoma frequently cause spontaneous internal bleeding, especially in organs such as the spleen or liver.
• Clotting disorders: Problems with blood clotting can lead to spontaneous bleeding, caused by factors such as anti-coagulant rodenticide poisoning, immune-mediated diseases destroying platelets, liver disease impairing clotting factor production, or disseminated intravascular coagulation (DIC).
• Blood vessel disorders: Rare congenital defects like Ehlers-Danlos syndrome weaken vessel walls, while some infections (e.g., tick-borne diseases or canine herpesvirus in puppies) cause vascular inflammation and bleeding.
• Post-operative bleeding: In some cases, blood vessels may reopen and bleed after recent surgery, even without new trauma.

When to see a vet

Any unexplained bleeding in your dog warrants prompt veterinary assessment, even if your dog appears otherwise well. Early diagnosis is critical to identify potentially life-threatening causes and start treatment promptly.

Observe the bleeding site carefully, monitor your dog’s overall condition, appetite, and behaviour, and note any other signs such as lethargy, loss of appetite, vomiting, or changes in urination or defaecation. This information will help your vet make an accurate diagnosis.

Responsible pet ownership and prevention

Maintaining your dog's health through regular vet check-ups, vaccinations, parasite control, and good dental care helps reduce the risk of many conditions that can cause bleeding. Promptly addressing infections, managing chronic diseases, and neutering pets when appropriate can also prevent reproductive-related bleeding issues.

Knowing your dog's normal behaviour and body condition aids early detection of problems, which can save lives.

Conclusion

Atraumatic bleeding in dogs can have diverse causes, ranging from common issues like ear mites to serious internal diseases such as haemangiosarcoma or clotting disorders. Understanding the possible sources and recognising symptoms early ensures timely veterinary care.

If you notice unexplained bleeding from any site on your dog, seek veterinary advice promptly. Responsible monitoring and preventive care support your dog's health and wellbeing for years to come.