SYMPTOM
Unexplained bleeding
Owners may observe unexplained bleeding in their pet.
Various conditions
This symptom can occur in multiple conditions and warrants further assessment.
Anticoagulant Rodenticide Toxicity
Ingestion of rat and mouse poisons depletes the vitamin K-dependent clotting factors needed for normal coagulation, typically producing spontaneous bleeding two to five days after exposure. This can appear as bruising, nosebleeds, or bleeding into body cavities, and access to baited sheds, farmland, or outbuildings raises the likelihood of exposure.
Immune-Mediated Thrombocytopenia
The immune system mistakenly targets and destroys circulating platelets, leaving too few available to seal small vessel injuries as they occur. This produces small pinpoint bruises (petechiae), larger bruises, or mucosal bleeding, and can arise on its own or secondary to infection, neoplasia, or certain medications.
Tick-Borne Infection
Organisms such as Anaplasma and Ehrlichia species, transmitted through tick bites, can suppress platelet numbers or interfere with their function, producing bleeding tendencies alongside fever and lethargy. Anaplasma phagocytophilum is carried by ticks already established across the UK, so this cause can arise without any travel history, while Ehrlichia canis is chiefly associated with dogs that have travelled or been imported from abroad, though a small number of cases have now been recorded in dogs with no travel history.
Hepatic Synthetic Failure
Most clotting factors are produced in the liver, so significant liver failure, whether from toxins, infection, or chronic disease, can leave too few functional factors circulating to support normal clot formation. Bleeding from this cause tends to develop alongside other signs of liver dysfunction, including jaundice and reduced appetite.
Vasculitis (Alabama Rot / CRGV)
Damage to the lining of small blood vessels produces skin lesions, swelling, and bruising typically below the knee or elbow, sometimes progressing to kidney injury. UK cases cluster in wet, muddy, wooded areas over the winter and spring months, though the precise environmental trigger remains unconfirmed.
Why timing matters
Early observation
Early recognition allows prompt assessment and intervention if needed.
Later presentation
Persistent or worsening signs may indicate progression requiring attention.
The significance of this symptom depends on its context, duration, and associated findings.
Conditions commonly associated
Angiostrongylus (Lungworm)
Coagulopathy causes bleeding that may manifest as bruising, prolonged wound bleeding, or internal haemorrhage.
Lymphoma in Dogs
Lymphoma can disrupt normal blood clotting mechanisms when it involves the bone marrow or causes secondary clotting abnormalities, leading to bleeding that may appear without obvious injury. In some cases, the tumour itself can erode into blood vessels or cause platelet dysfunction.
Alabama Rot (CRGV)
Alabama rot involves damage to small blood vessels in the skin and kidneys, which can manifest as skin lesions with bleeding or ulceration, often appearing on the limbs or body. The vascular injury underlying this condition may cause visible bleeding that seems disproportionate to any obvious external cause.
Pemphigus
Pemphigus causes breakdown of connections between skin cells, leading to fragile blistering lesions that rupture easily and may bleed when the surface is disrupted. The erosions and crusts that develop can appear as areas of unexplained bleeding, particularly when grooming or minor contact occurs.
Transitional Cell Carcinoma
Transitional cell carcinoma can cause bleeding from the urinary tract when tumour tissue erodes through the bladder or urethral lining, often appearing as blood in urine without other obvious explanation. The fragile, abnormal tissue may bleed intermittently, sometimes producing visible blood outside the context of urination.
Multiple Myeloma
Abnormal proteins produced by the tumour can interfere with normal blood clotting, leading to unexpected bruising or bleeding from the nose or gums.
Acute Hepatic Failure
The liver produces clotting factors, so acute failure can leave the blood unable to clot normally, resulting in unexplained bruising or bleeding.
Anaplasmosis
Anaplasma infection can lower platelet numbers, occasionally leading to unexpected bruising or bleeding.
Anticoagulant Rodenticide Toxicity
Anticoagulant rodenticides block the recycling of vitamin K, leaving the blood unable to clot and producing unexplained bleeding from the gums, nose or elsewhere.
Ehrlichiosis
A fall in platelet numbers during ehrlichiosis impairs normal clotting, so small bruises, nosebleeds or bleeding gums can appear without an obvious cause.
When to explore further
When the symptom is persistent or worsening
When other signs are present alongside
When daily activities or quality of life are affected
When there is uncertainty about the cause
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS