SYMPTOM
Unexplained bleeding
Bleeding or bruising appears with no injury to account for it, or carries on far longer than a small wound would explain. It may show as a nosebleed, blood at the gum line, tiny purplish-red spots (petechiae) or larger bruises on the gums or skin, black tarry stools, blood in the urine or vomit, or bleeding in the eye. Bleeding into the chest or abdomen cannot be seen from outside: the outward signs are pale gums, weakness, laboured breathing or collapse.
Angiostrongylus (Lungworm)
Infection with the lungworm Angiostrongylus vasorum can disturb clotting, and bleeding may be the only abnormality recognised, with no cough or other breathing signs. In one published study of 180 infected dogs, 65 (36.1%) had signs of bleeding, and survival to hospital discharge was 76.9% in the bleeding dogs against 94.8% in those without bleeding.
Anticoagulant Rodenticide Toxicity
Ingestion of anticoagulant rat and mouse poisons depletes the vitamin K-dependent clotting factors needed for normal coagulation, with bleeding typically first noted three to seven days after a toxic dose is eaten, so a dog can look well in the days between eating bait and the first bleed. 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.
Cutaneous and Renal Glomerular Vasculopathy (Alabama Rot)
Damage to small blood vessels (a thrombotic microangiopathy) produces skin sores and swelling, mostly on the lower limbs, sometimes followed by acute kidney injury and, in most dogs, a fall in platelet numbers. In one UK analysis 92% of diagnoses fell between November and May and cases were generally associated with woodland. The cause remains unknown.
Why timing matters
Early observation
The first visible sign, such as a nosebleed or a scatter of pinpoint spots, may be the only outward evidence of a clotting failure that is already advanced. Dogs that bleed spontaneously from immune-mediated thrombocytopenia usually have platelet counts below about 30,000 per microlitre at diagnosis, and often below 10,000.
Later presentation
Bleeding into the chest, abdomen, brain or spinal cord can follow with no further blood seen externally, and bleeding into a body cavity can lead to sudden collapse. In a published series of 15 dogs with lungworm whose main complaint was unexplained bleeding, four died, three of them on the day of admission.
The amount of blood visible is not a guide to severity, and nothing seen at home separates one cause from another. Several causes respond to targeted treatment once identified, which makes the time taken to reach a diagnosis the main thing that can be changed.
Conditions commonly associated
Angiostrongylus (Lungworm)
Lungworm infection can disturb clotting, so bleeding may appear as bruising, prolonged wound bleeding or internal haemorrhage, sometimes with no cough.
Lymphoma in Dogs
Lymphoma can lower platelet numbers and disturb normal clotting, more so in advanced disease, so bruising or bleeding may appear without obvious injury.
Alabama Rot (CRGV)
Alabama rot damages small blood vessels in the skin and kidneys, producing skin sores and swelling, mostly on the lower limbs. Platelet numbers fall in most affected dogs, which is why the condition is considered when bleeding or bruising is unexplained.
Transitional Cell Carcinoma
Transitional cell carcinoma of the bladder or urethra commonly causes blood in the urine, often with straining or frequent 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 and altered platelet function during ehrlichiosis impair normal clotting, so small bruises, nosebleeds or bleeding gums can appear without an obvious cause.
When to explore further
When any bleeding or bruising has no injury to explain it, including a single nosebleed or a few pinpoint spots on the gums, because platelet numbers and clotting times can only be measured by blood tests
When pale gums, weakness, laboured breathing or collapse appear alongside any bleeding, as these are the outward signs of blood loss into the chest or abdomen
When there are black tarry stools, blood in the urine or vomit, or bleeding from a small wound that does not stop
When there has been known or possible access to rat or mouse bait in the previous week, even where the dog seems well, because bleeding typically starts three to seven days after the bait is eaten
Details that help a veterinary assessment include where the bleeding was seen and when it began, gum colour, any possible access to rat or mouse bait over the previous week (with the product packaging if it exists), lungworm prevention history, tick exposure, travel or import history, recent woodland walks, and all medicines and supplements given.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS