Testing for Pallor

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

What is pallor?

Pallor means paleness or loss of color. In pets, pallor is usually detected as a loss of color in the gums and inner eyelids. These are normally a light rosy pink, but when pallor develops, they become faint pink to white. Pallor is a sign of illness.

What causes pallor?

Pallor in pets is usually a sign of anemia or “thin” blood, but can also be a sign of poor circulation due to conditions such as heart disease or shock.

How can you determine the cause of pallor in my pet?

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. A detailed history may help identify the underlying problem. For example, pallor in a pet with a history of trauma might be due to internal bleeding, while a history of progressive weight loss might signal longstanding illness such as cancer or organ failure.

"A pet’s history is the information you give your veterinarian about your pet’s illness. A detailed history may help identify the underlying problem."

Physical examination involves looking at all parts of the body, and typically includes 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). Physical examination may provide clues about what is causing pallor in a pet. For example, abnormal heart or lung sounds might indicate heart disease; abdominal palpation may reveal the presence of a cancerous tumor, causing blood loss and anemia.

When the cause of pallor cannot be determined from the history and physical examination, further testing is needed, and 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 are recommended?

The following screening tests are recommended:

Complete Blood Count (CBC)

This is a simple blood test that provides information about the three different cell types in the blood. These include the 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 (see handout “Complete Blood Count” for more information).

1) Red Blood Cells. The most common cause of pallor is anemia, which means there are not enough red blood cells or enough hemoglobin to carry oxygen to the body. The CBC will confirm that anemia is present. It will also determine the severity of the anemia, how long it has been going on, and what might be causing it.

There are many causes of anemia, but in general, anemia is caused by:

  • loss of red blood cells (bleeding)
  • destruction of red blood cells (immune-mediated disease; cell breakage)
  • failure of the bone marrow to make new red blood cells (bone marrow disease)

Examination of the red blood cells helps to classify the anemia. For example:

  • Small and pale red blood cells suggest iron deficiency anemia associated with longstanding bleeding or poor nutrition.
  • Small, densely colored red blood cells called spherocytes are often associated with immune-mediated destruction of red blood cells, primarily in dogs.
  • Oddly shaped red blood such as acanthocytes, which are spikey, or broken red blood cells called schistocytes may point to an underlying tumor, liver disease, or damaged blood vessels.
  • Large numbers of young red blood cells, called polychromatic erythrocytes indicate the bone marrow is working properly and is responding to a demand for new red blood cells.
  • Persistently low numbers of polychromatic erythrocytes in an anemic pet suggests the bone marrow is having difficulty producing new red blood cells.

2) Platelets. The CBC also provides information about platelets, which are part of the body’s blood clotting system. If the number of platelets falls too low then sudden bleeding may occur, leading to anemia and pallor.

3) White Blood Cells. A CBC reports the total number of white blood cells and describes the different types of white blood cells present. Anemia and pallor may develop due to underlying inflammation, infectious disease, or cancer.

  • High numbers of white blood cells usually indicate inflammation or infection, but may signal leukemia (bone marrow cancer).
  • Abnormal cells in the blood is a sign of underlying bone marrow disease including leukemia.

Serum Biochemistry Profile

This refers to the chemical analysis of serum, which is the pale-yellow liquid part of blood that remains after the cells and clotting factors have been removed. Serum contains many substances including enzymes, proteins, lipids (fats), glucose (sugar), hormones, electrolytes, and metabolic waste products.

"Changes and abnormalities found in the biochemistry profile can help to diagnose a variety of diseases and disorders"

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 handout “Serum Biochemistry” for more information).

Any longstanding disease associated with liver, pancreas, and kidneys may result in mild to moderate anemia and pallor. Sometimes, serum biochemistry helps to confirm a diagnosis of immune mediated anemia, which is another important cause of anemia and pallor.

Three-part illustration explains the common screening tests: complete blood test, serum biochemistry, and urinalysis. Part 1: A complete blood test (CBC) analyzes the cellular components of the blood. Illustration shows red blood cells, white blood cells, and platelet cells. Part 2: Serum biochemistry refers to the chemical analysis of the liquid component of blood that remains after the cells and clotting factors have been removed. Illustration shows a test tube with a small amount of red at the bottom (blood cells), and a pale-yellow liquid (serum) at the top. Part 3: Urinalysis includes a dipstick test of the chemical properties of the urine. Illustration shows a cup of urine and some small, paper dipsticks with stripes of various colors that will test for various chemicals in the urine.


This is a simple test that analyzes the physical and chemical composition of the 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 more information).

"Urinalysis should always be done to look for signs of urinary bleeding that might be contributing to pallor."

Urinalysis should always be done to look for signs of urinary bleeding that might be contributing to pallor. Urinary bleeding can be caused by many conditions, including bladder stones, urinary infection, infectious disease, kidney injury, and cancer. All of these disorders can be identified by examining urine for red blood cells, white blood cells, crystals, bacteria, or cancerous cells.

What additional tests might be recommended?

There are a variety of additional tests that may be recommended depending on the results of a pet’s history, physical examination, and screening tests. Some examples of additional tests include:

  • Tests for heart disease such as X-rays, electrocardiography, echocardiography, and specific blood tests that detect heart muscle damage.
  • Bone marrow aspiration and evaluation look for bone marrow disease or bone marrow cancer.
  • Coagulation testing is done if there is unexplained bleeding or if a blood clotting disorder is suspected.
  • Parasite tests check for internal or external parasites, especially in puppies and kittens since they are more likely to carry parasites.
  • Tests for organ disease may include organ-specific tests (liver, kidney), function tests, as well as X-ray, ultrasound, or biopsy.
  • Tumor evaluation may include X-ray, ultrasound, or biopsy by fine needle aspiration or tissue biopsy.
  • Tests for infectious disease include blood tests for specific agents such as feline leukemia virus, feline immunodeficiency virus, Leptospira, Rickettsia, or Mycoplasma.
  • Iron tests measure levels of iron in the blood or bone marrow if iron deficiency anemia is suspected.
  • Fecal occult blood test detect bleeding into the gastrointestinal tract.
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