There are a number of reasons for a dog coughing up blood. This condition is called hemoptysis, or the expectoration of blood or blood-dried mucus from the respiratory tract. Irritation or inflammation can cause blood to be produced from the larynx, trachea or lungs. The severity of the underlying issue will depend upon a number of factors, but usually if a dog is coughing up blood, it's almost always a significant matter of concern. Other factors will come into play when attempting to determine and diagnose the cause, such as the amount of blood that is present, the color (i.e., whether it's fresh or dried blood), whether it's accompanied by any mucus and any other symptoms which may be present.
Pulmonary Vascular Disease
Pulmonary vascular disease in dogs can be caused by one or more of several underlying conditions. Heart disease associated with blood clots may result in your dog coughing up blood. A heartworm infection increases the risk for pulmonary thormboembolism, which may cause blood or bloody fluid to be pushed into the airways. Dogs with pancreatitis, some types of anemia, lung cancer, systemic bleeding, inflammatory diseases and hyperadrenocorticism will also be at an increased risk for pulmonary disorders.
Tuberculosis
Tuberculosis is a bacterial infection that can affect your dog. This condition may produce upper respiratory symptoms and cause dogs to cough up bloody mucus or phlegm. Tuberculosis is uncommon in dogs, but typically contracted through inhalation, so the lungs would be a primary target for infection. If coughing up blood is accompanied by symptoms such as jaundice, weight loss, increased thirst and urination, vomiting and dehydration, a diagnosis of tuberculosis is possible.
Hematemesis
Hematemesis is the technical term for vomiting blood. While a dog coughing blood likely has respiratory problems, vomiting blood generally points to problems with the digestive tract. Throat or stomach ulcers, cancer of the digestive tract, blood coagulation problems and severe inflammatory conditions may cause hematemesis. It's important to note that bloody phlegm produced by a dog's cough may easily be swallowed. Ingestion of sharp and foreign objects, like bones or other materials, may get stuck in the esophagus or severely irritate the throat causing bleeding. Additionally, consumption of toxins like insecticides or rodenticides could produce blood. If blood is coughed up and swallowed in significant amounts, signs of blood may be discovered in vomit or stool.