Testing for Unexplained Bleeding

By Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

What is “unexplained” bleeding?

Most bleeding (or hemorrhage) is caused by trauma. There is usually a wound or a history of injury to explain why a pet is bleeding. Typically, the bleeding stops when a blood clot forms at the site of injury.

However, sometimes bleeding occurs when there is no wound and no history of injury. In these cases, the bleeding cannot be explained. For example, a pet may suddenly start bleeding from the nose or start passing blood in the urine for no apparent reason. Often there is bleeding under the skin or on the gums, which is seen as tiny “pinpoint” spots of hemorrhage called petechiae or as larger blotches called ecchymoses.

Unexplained bleeding is worrisome because it suggests there is a problem with the body’s blood clotting or coagulation system. Disorders of the coagulation system can arise for many reasons including shortages of coagulation factors (clotting proteins), a shortage of platelets (a type of blood cell), defective platelets, and serious systemic disease affecting the whole body.


How do we determine the cause of unexplained bleeding in my pet?

The search for answers starts with a complete history and physical examination. A pet’s “history” is the information you give the veterinarian about your pet’s illness. For example, it would be important to mention whether your pet has had contact with rat poison or is known to hunt for mice or rats. You would also want to mention medications or supplements your pet has received recently, or describe any signs of illness your pet is showing.

Physical examination involves looking at all parts of the body, checking for petechiae and ecchymoses, listening to the heart and lungs with a stethoscope, and “palpating” the abdomen (gently squeezing or prodding the abdomen with the fingertips to detect abnormalities of the internal organs). In dogs, it would be important to note if the pet is a purebred, since purebred dogs are more likely to have hereditary blood clotting problems.

If the cause of the bleeding cannot be found, your veterinarian may recommend doing screening tests. These are a series of simple tests that provide information about the overall health of the pet and may provide further clues about the underlying problem.


What screening tests would be recommended?

The most common screening tests include complete blood count (CBC), serum biochemistry profile, and urinalysis. In addition, special tests to evaluate the coagulation system may be recommended including coagulation profile, von Willebrand's factor assay (in dogs), and possibly buccal mucosal bleeding time (BMBT).

What might these screening tests tell us?testing_for_signs_of_bleeding-1

(a) The CBC (complete blood count) provides information about the three different cell types in the blood. These are: 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 cells types, and identifies the presence of abnormal cells. (See article Complete Blood Count).

In a pet with unexplained bleeding the most important information is the platelet count. This is a measure of the number of platelets found in the blood.

"if the platelet count is too low, then unexplained bleeding may occur..."

Platelets are an essential part of the coagulation process and if the platelet count is too low, then unexplained bleeding may develop. A low platelet count is called thrombocytopenia. There are many causes of thrombocytopenia. A few examples include: immune-mediated destruction of platelets, decreased production of platelets in the bone marrow, and increased use of platelets by the body.

Sometimes the CBC provides clues about the cause of the thrombocytopenia. For example, if there are too many white blood cells in the blood then severe inflammation or infection may be present, which can cause thrombocytopenia. If there are too few white blood cells then a viral infection may be damaging the bone marrow and causing platelet numbers to fall. If there are abnormal cells in the blood, then leukemia (bone marrow cancer) may be causing thrombocytopenia.

"If bleeding is severe… a blood transfusion may be needed."

The CBC also counts the number of red blood cells in the blood. If bleeding is severe or has been going on for a long time then the number of red blood cells may be very low. Specific treatment such as a blood transfusion may be needed to bring the number of red blood cells back to normal.

(b) Serum biochemistry refers to the chemical analysis of serum, which is the pale yellow liquid part of blood that remains after the cells and clotting factorshave been removed. Serum contains many substances including enzymes, proteins, lipids (fats), glucose (sugar), hormones, electrolytes, and metabolic waste products. Testing for these substances provides information about the health of various organs and tissues in the body, as well as the metabolic state of the animal. Changes and abnormalities found in the biochemistry profile can help to diagnose a variety of diseases and disorders. (See article Serum Biochemistry).

(c) Urinalysis 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 article Urinalysis).

Severe systemic disease such as liver or kidney failure can interfere with normal coagulation. Serum biochemistry and urinalysis help to determine if such diseases are present and might be causing a pet’s unexplained bleeding.


(d) Coagulation tests

1. Coagulation profile. This blood test determines if there are proper levels of clotting factors in the blood. Abnormal results indicate there is a shortage of one or more clotting factors, which would explain why a pet is bleeding. This test is especially useful in diagnosing warfarin poisoning (rat poison). If the coagulation profile is normal, then proper levels of clotting factors are present and rat poison is not likely involved.

2. Von Willebrand's factor (VWF) is a protein found in the blood that makes platelets “sticky” and helps them attach to a damaged blood vessel to get the clotting process started. Von Willebrand’s factor also helps other coagulation factors work better. A shortage of VWF is found in dogs, and many purebred dogs have an inherited shortage of von Willebrand's factor. A test for von Willebrand's factor should be done in any dog with unexplained bleeding, especially if it is a purebred.

3. A buccal mucosal bleeding time (BMBT) is a test that evaluates the ability of platelets to stick to each other to make a platelet “plug” whenever a blood vessel is damaged. The platelet plug is the first step in the coagulation process and is essential for proper clot formation. The test involves making a tiny precise cut on the inside of the upper lip and measuring how long it takes for bleeding to stop. If the BMBT is normal it means there are enough platelets in the blood and that the platelets are working properly.

Sometimes a patient will have normal numbers of platelets but the BMBT is abnormal. This indicates a platelet function defect, which means the platelets are not working properly and can’t form a platelet plug. Some drugs, such as aspirin, interfere with platelet function and can lead to unexplained bleeding.

What additional tests might be recommended?

Screening tests and coagulation tests will likely identify the cause of the unexplained bleeding. However, there may be underlying problems that need to be investigated further.

Some examples:

  • The CBC may show the unexplained bleeding is due to severe thrombocytopenia. If the thrombocytopenia appears to be due to a bone marrow disorder then bone marrow collection and examination may be recommended to understand the underlying problem.
  • If the serum biochemistry shows the unexplained bleeding is due to severe liver disease, then tests may be recommended to learn more about the liver problem. Testing may include measuring serum bile acids, doing X-rays or ultrasound, and possibly taking a biopsy.


  • If infectious disease is thought to play a role, then tests for specific infectious agents such as Ehrlichia in   dogs, and Feline Leukemia Virus or Feline Immunodeficiency Virus in cats, would be appropriate.

  • If platelet numbers are normal but the unexplained bleeding points to a problem with platelet function, then specific platelet function tests may be helpful. These tests are available only in a few specialized research facilities.
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