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Testing for Pallor

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

Diagnosis, Pet Services

What is pallor?

Pallor means paleness or loss of color. In pets, pallor is usually detected as a loss of color from 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 is usually a sign of anemia or poor circulation "

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 we determine the cause of pallor in my pet?testing_for_signs_of_pallor-1

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. 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.

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 an  intestinal parasites causing blood loss and anemia.

"When the cause of pallor cannot be determined… further testing is needed…”

When the cause of pallor cannot be determined from the history and physical examination, then 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 reccommended?

The most common screening tests are complete blood count (CBC), serum biochemistry profile, and urinalysis.

(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).

(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 analyses 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).

What can these screening tests tell us?

(a) The complete blood count (CBC).

1. Red Blood Cells

The most common cause of pallor is anemia, which means there aren’t 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’s 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)
"The most common cause of pallor is anemia."

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

  • Small pale red blood cells suggests 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 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.


"Anemia and pallor may develop due to underlying inflammation, infectious disease, or cancer."

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 indicates 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.

(b)  A Serum biochemistry profile assesses many organ systems including the liver, pancreas and kidneys. Any longstanding disease associated with these organs may result in mild to moderate anemia and pallor. Sometimes, serum biochemistry helps to confirm a diagnosis of immune mediated anemia, which is an important cause of anemia and pallor.

"A urinalysis should always be done to look for signs of urinary bleeding…”"


(c) 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 things such as 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…"

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 would include:testing_for_signs_of_pallor-4

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

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