What causes coughing?
Coughing can have many different causes. A few examples include:
- Inflammation or irritation of the respiratory passages due to allergies or inhaled foreign material such as food particles, dust, smoke, or plant fragments
- Infection of the respiratory system due to bacteria, viruses, fungi, or parasites
- Pneumonia (infection of the lungs)
- Tracheal collapse caused by a weak trachea (windpipe) that flattens on itself when the pet inhales (breathes in) rather than staying open like a rigid pipe
- Lung or airway tumors
- Heart disease, especially congestive heart failure
How do we determine the cause of my pet’s cough?
The search for answers starts with a complete history and physical examination. A pet’s history is the information you give your veterinarian about your pet’s illness. In a coughing pet, this would include details such as how long the cough has been present, possible contact with other pets, and whether the cough is triggered by any particular circumstances.
"The search for answers starts with a complete history and physical examination."
History can be very helpful when determining the cause of your pet’s cough. For example, a dog that develops a cough after staying in a boarding kennel may have a respiratory infection called kennel cough; a toy breed dog that coughs only when it is excited may have a collapsing trachea; a coughing cat with a history of being outdoors may have feline heartworm disease or lungworms.
A thorough physical examination involves looking at all parts of the body, examining the mouth and throat, and listening to the heart and lungs with a stethoscope. This examination may provide clues about the cause of the cough. For example, a pet with an irregular heartbeat or heart murmur may have heart disease, the presence of loud raspy sounds in the lung may indicate underlying pneumonia, a dog who coughs easily when the throat is touched may have tracheitis or a collapsing trachea.
History and physical examination provide important information, but additional diagnostic tests may be needed, and your veterinarian may recommend screening tests. These are a series of simple tests that provide information about the overall health of your pet and may provide further clues about the underlying problem.
What screening tests might be recommended, and what can they tell us?
In a coughing pet, the recommended screening tests could include a complete blood count, serum biochemistry profile, urinalysis, parasite tests, and chest X-rays (radiographs). Further testing may be recommended, depending on the results of the initial screening tests.
Complete blood count (CBC)
This is a simple blood test that provides information about the different cell types in the blood. These include red blood cells, which carry oxygen to the tissues; white blood cells, which fight infection and respond to inflammation; and platelets, which help the blood to clot.
The CBC provides details about the number, size, and shape of the various cell types and identifies the presence of abnormal cells in circulation. See handout "Complete Blood Count" for further information.
In a coughing pet, a CBC might show:
- Anemia (a decrease in the number of red blood cells and the amount of hemoglobin). This could be due to bleeding in the respiratory tract, or could be a sign of longstanding respiratory inflammation or other chronic disease.
- Polycythemia (an increase in the number of red blood cells and the amount of hemoglobin). This is seen with longstanding lung problems and represents the body’s attempt to increase the amount of oxygen the blood can carry to the tissues.
- Increased numbers of white blood cells. Increased numbers of neutrophils (a type of white blood cell) often signal an underlying infection. Increased numbers of eosinophils (another type of white blood cell) are associated with allergies and parasitic infections.
Serum biochemistry profile
Serum biochemistry profile refers to the chemical analysis of serum, which is the liquid part of blood that remains after the cells and clotting factors have been removed. There are many substances in serum, including proteins, enzymes, fats, sugars, hormones, and electrolytes. Measuring the levels of these substances provides information about the organs and tissues in the body, as well as the metabolic state of your pet. Changes and abnormalities found in the biochemistry profile can help to diagnose a variety of diseases and disorders. See handout "Serum Biochemistry" for further information.
Urinalysis
This is a simple test that analyzes the physical and chemical composition of urine. It measures how well the kidneys are working, identifies inflammation and infection in the urinary system, and helps to detect diabetes and other metabolic disturbances. Urinalysis is important for the proper interpretation of the serum biochemistry profile and should be done at the same time as blood testing. See handout "Urinalysis" for further information.
In a coughing pet, serum biochemistry and urinalysis testing help to determine if a cough is part of a larger systemic illness. A systemic illness is a disorder that affects many organs and body systems at one time and can involve the lungs. If serum biochemistry and urinalysis are abnormal, then systemic disease may be causing the cough and further investigation of the underlying illness is recommended. However, if the serum biochemistry and urinalysis are normal, then the cough likely involves only the respiratory system and further testing would investigate problems affecting only the lungs and airways.
Parasite testing
In a coughing pet, both stool and blood should be tested for parasites.
- Stool tests: Parasites that infect the lungs can be detected by examining a pet’s stool for parasite eggs or larvae (baby worms). The two most common stool tests are fecal flotation and fecal Baermann. Both tests require only a small amount of fresh stool. Fecal flotation identifies the presence of parasite eggs in stool. Fecal flotation can be done in-house at many clinics, or at a referral laboratory. Fecal Baermann identifies the presence of parasite larvae in stool. It is a more complicated test and samples are usually submitted to a referral laboratory for testing.
- Blood test: Testing for heartworm (Dirofilaria immitis) may be required if a pet lives in an area where heartworm infection is common or has visited an area where heartworm infection occurs. Heartworm disease is seen mostly in dogs, but is also seen in cats, so both cats and dogs should be tested. Even a dog on a preventative program should be tested for heartworm infection if a cough develops. The test requires a simple blood sample.
Chest X-rays (radiographs)
X-rays can be performed in-clinic and may reveal tumors, fluid in or around the lungs, or abnormal heart size/shape. A narrow trachea may also be identified, which supports tracheal collapse.
What specific tests may be required if my pet’s cough just involves the respiratory system?
Several tests might be recommended depending on the results of a pet’s history, physical examination, and screening tests. A, few examples would include:
- More advanced imaging studies. Ultrasound of the chest would be recommended to look for evidence of heart disease, tumors, fluid accumulation in the chest, fungal infection, or parasites.
- Bronchoscopy. This test allows your veterinarian to look directly down the trachea and respiratory passages to identify problems (see details below).
- Transtracheal wash and bronchoalveolar lavage. These are techniques that collect material from the trachea and lungs for microscopic examination to look for causes of cough (see details below).
- Sputum cytology. Sometimes a pet coughs up material and “spits” it on the floor. This material is called sputum, and it can be examined microscopically for evidence of organisms, parasites, inflammation, cancer, etc.
- Fine needle aspiration of the chest (thoracocentesis). This technique involves inserting a needle through the body wall, into the chest cavity, and extracting fluid that has built up there. This fluid is sent to a veterinary referral laboratory for examination by a veterinary pathologist. This test can identify the presence of infection, inflammation, fungal disease, parasites, and cancer.
- Fine needle biopsy. This is like fine needle aspiration, except that samples are collected from solid tissue, such as a lung mass.
- Culture and sensitivity. If bacterial infection is suspected, culture and sensitivity tests identify what types of bacteria are present and which antibiotic is best to treat the infection. Samples for culture and sensitivity can be collected by transtracheal wash, bronchoalveolar lavage, or thoracocentesis.
- Fungal serology. This is a blood test that helps to detect certain types of fungal infection.
- Testing for heart disease. This includes chest X-rays, cardiac echocardiogram, electrocardiogram, and possibly ProBNP blood testing (detects an enzyme released from damaged heart muscle).
When is a transtracheal wash indicated?
A transtracheal wash is indicated when a cough is due to a problem in the windpipe (trachea) or the large airways of the lung, called bronchi. A transtracheal wash involves flushing a small amount of sterile fluid into the trachea and then quickly suctioning or “re-aspirating” the fluid back into the syringe. The aim is to collect secretions, cellular material, and any infectious organisms such as bacteria, fungi, or parasites present in the trachea. There are two ways of performing a transtracheal wash.
- The first method is done with mild sedation and local freezing of the throat area. The procedure involves making a small cut in the skin over the larynx (voice box) and passing a special catheter (long, tiny tube) through the skin and into the trachea. A syringe of sterile fluid is attached, and fluid is flushed into the trachea and then quickly re-aspirated back into the syringe. This method is usually needed in medium to large breed dogs.
- The second method is done under general anesthetic with the placement of an endotracheal tube (a large tube that is routinely placed in the trachea during general anesthesia). This is sometimes called an endotracheal wash. A small catheter is threaded down the endotracheal tube, into the trachea, and a syringe is used to flush sterile fluid into the trachea. The fluid is then re-aspirated, as described for the first method.
Bronchoscopy involves passing a small, flexible, fiberoptic endoscope down the windpipe to look directly at the lining of trachea and bronchi. If there are signs of inflammation, bleeding, or tumors, small biopsies can be collected for later microscopic examination. Bronchoscopy can also identify the presence of certain parasites that live in the airways and can detect malformations such as collapsing trachea. A general anesthetic is required for bronchoscopy.
Bronchoalveolar lavage is used to collect samples from deep in the lung. The technique involves passing an endoscope down the trachea and into a small airway in the lung. Then, like a transtracheal wash, a small amount of sterile fluid is flushed into the airway and then quickly re-aspirated. The collected material is sent to a veterinary pathologist for examination. A general anesthetic is required for bronchoalveolar lavage.
Once the cause of the cough has been determined, your veterinarian will then be able to develop the most appropriate treatment plan.
