Nosebleeds can occur for a lot of reasons. In older dogs a major concern would be nasal tumours or nasal infections. Tumours can be pretty hard to find even with endoscopy and X-rays in some cases but the tests for this make it less likely. In any age dog bleeding disorders need to be considered when nosebleeds occur. Ehrlichia canis, immune mediated thrombocytopenia, immune mediated hemolytic anaemia and other causes of bleeding should all be considered.

In older dogs a fairly common cause of bleeding disorders is hemangiosarcoma, a type of tumour. Heartworms can cause nosebleeds in the later stages of the disease. It can be difficult to identify the cause of bleeding disorders.