Testing for Signs of Pallor

What is pallor?

By definition, pallor means paleness or absence of skin coloration. Because our pets are covered with a thick hair coat, we usually cannot appreciate pale skin, but pallor may be seen on mucous membranes such as the gums or inner eyelids, or on the skin of the ears.

What causes pallor?

"Pallor may be caused by anemia or by circulatory problems such as cardiac disease."

Pallor may be caused by anemia or by circulatory problems such as cardiac disease.

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

A history and thorough physical examination may give us some 'clues' regarding the cause of pallor in your pet. For example, cardiac disease may be suggested by abnormal heart or lung sounds, while abdominal palpation may reveal the presence of a mass within the abdomen that could be the source of anemia through chronic blood loss.

Often no specific cause of pallor is found on initial examination. We must then undertake a series of screening tests to try to determine its underlying cause.

What screening tests are suggested?

Certain screening tests are suggested when the underlying cause of pallor is not readily apparent following the history and physical examination. These tests include a complete blood count (CBC), a serum biochemistry profile, and a urinalysis.

If specific problems such as cardiac disease are identified on physical examination, then specific additional testing such as electrocardiography or echocardiography will be required. Such cardiac testing is discussed elsewhere.

What might these screening tests indicate?

A complete blood count (CBC) provides an evaluation of the red blood cell, the white blood cell, and the platelet components of a blood sample. A hematology (blood) analyzer will provide us with the total numbers of these cells, and evaluation of a blood smear will allow us to look at the physical characteristics of these cells.

"Anemia is the most common cause of pallor."

Anemia is the most common cause of pallor. Since there are many different causes of anemia, an evaluation of the red blood cell parameters is of utmost importance. The PCV (packed cell volume), total red blood cell numbers, and the hemoglobin measurement will tell us the degree of anemia present. Additional characteristics of the red blood cells will be evaluated on the blood smear. These include assessment of the average cell size and average hemoglobin content of the red blood cells. Such characteristics are important as they may give us clues to the underlying cause of the anemia. For example, small red blood cells with a decreased amount of hemoglobin are associated with iron deficiency anemia associated with chronic blood loss.

Changes in the shape of the red blood cells may also help us. Small, dense red blood cells called spherocytes may be associated with immune mediated destruction of red blood cells. Spiculated (spiky) red blood cells called acanthocytes are often found in association with underlying tumors. The degree of bone marrow response to the anemia can be indirectly evaluated on the blood smear. Newly produced red blood cells, called polychromatic erythrocytes (literally 'multicolored red blood cells'), are often found in large numbers in response to anemia due to immune mediated destruction of red blood cells, whereas low numbers of polychromatic erythrocytes are noted in association with iron deficiency anemia from chronic blood loss. A special stain can be used to make these polychromatic erythrocytes stand out for ease of counting. 

The CBC also provides us with total platelet numbers. Platelets are involved in the clotting process by forming a "plug" at the site of any blood vessel injury. Occasionally anemia is due to hemorrhage or blood loss from inadequate platelet numbers.

"Anemia (with subsequent pallor) may be a consequence of underlying inflammatory or infectious conditions."

Anemia (with subsequent pallor) may be a consequence of underlying inflammatory or infectious conditions. A CBC provides us with an evaluation of total white blood cell numbers and with a 'differential' of their types so such conditions can be identified. Occasionally anemia may be the result of an underlying bone marrow disorder such as leukemia. In some instances, abnormal white blood cells that are present due to underlying leukemia are identified.

A serum biochemistry profile provides us with an overall assessment of many organ systems including the liver, pancreas and kidneys. Any chronic disease associated with these organs may result in mild to moderate degrees of anemia. Premature destruction of red blood cells may be associated with some disease conditions. For example, severe diabetes mellitus may result in marked decreases in blood phosphorus levels, which will cause red blood cells to rupture.

A urine dipstick tests the properties of urine.

"It is important to rule out the urinary tract as a source of blood loss."

A urinalysis provides us with an assessment of the physical and chemical characteristics of a urine sample. It is important to rule out the urinary tract as a source of blood loss. This is done by evaluating the urine using special chemical strips that detect the presence of blood in the urine, and by looking microscopically at the cells present in a urine sample. In addition to looking for red blood cells, the presence of unusual urinary tract lining cells is also evaluated. Such unusual cells might indicate the presence of a bleeding tumor in the bladder.

What additional tests might be indicated?

"Any additional testing is entirely dependent upon the combined results of the physical examination, history, and screening tests."

Any additional testing is entirely dependent upon the combined results of the physical examination, history, and screening tests.

If we suspect an underlying bone marrow disorder as a cause of the anemia and pallor, then bone marrow collection and evaluation are indicated.

If underlying organ disease or a tumor is suspected, then further tests might include imaging studies (such as x-ray or ultra-sound) or sampling (fine needle aspiration biopsy or tissue biopsy) of the organ or mass.

If infectious disease is thought to play a role in the anemia, then blood tests for infectious agents such as feline leukemia virus or feline immunodeficiency virus may be undertaken.

Iron deficiency anemia may require confirmation by serum iron tests.

Suspected bleeding into the gastrointestinal tract may be confirmed by a fecal occult blood test.