Testing for Unexplained Bleeding

By Malcolm Weir, DVM, MSc, MPH; Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

What is unexplained bleeding?

Most bleeding (hemorrhage) is caused by trauma. A wound or a history of injury usually explains why a pet is bleeding. Typically, the bleeding stops when a blood clot forms at the injury site. 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 pass blood in the urine for no apparent reason. There is often bleeding under the skin or on the gums, seen as tiny pinpoint spots of hemorrhage called petechiae or larger blotches called ecchymoses.

Unexplained bleeding is worrisome because it suggests 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.

"Unexplained bleeding is worrisome because it suggests a problem with the body’s blood clotting or coagulation system."

How will my veterinarian 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.

A 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 essential to note if they are purebred, as they are more likely to have hereditary blood clotting problems.

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

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 can these screening tests tell us?

(a) The complete blood count (CBC) provides information about the three cell types in the blood: 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 clot. The CBC provides details about the number, size, and shape of the various cell types and identifies the presence of abnormal cells. See the handout “Complete Blood Count” for more information.

In a pet with unexplained bleeding, the most essential information is the platelet count, a measure of the number of platelets in the blood. 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.

"In a pet with unexplained bleeding, the most essential information is the platelet count, a measure of the number of platelets in the blood."

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

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, the number of red blood cells may be deficient. 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 (the pale-yellow liquid part of blood that remains after the cells and clotting factors have been removed). The 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 diagnose various diseases and disorders. See the handout “Serum Biochemistry” for more information.

(c) Urinalysis is a simple test that analyzes urine's physical and chemical composition. It measures how well the kidneys are working, identifies inflammation and infection in the urinary system, and helps detect diabetes and other metabolic disturbances. Urinalysis is necessary for adequately interpreting the serum biochemistry profile and should be done at the same time as blood testing. See the handout “Urinalysis” for more information.

Severe systemic diseases like 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:

  • Coagulation profile. This blood test determines if there are proper levels of clotting factors in the blood. Abnormal results indicate a shortage of one or more clotting factors, which would explain why a pet is bleeding. This test is instrumental 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.
  • 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 in purebred dogs.
  • 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, there are enough platelets in the blood, and the platelets are working correctly.

Sometimes a patient will have a normal amount of platelets, but the BMBT is abnormal. This indicates a platelet function defect, which means the platelets are not working correctly 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 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 that 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, radiographs (X-rays), ultrasound, or biopsy.
  • If an infectious disease is suspected, tests for specific infectious agents, such as Ehrlichiain dogs and feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV) 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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