Cornell University College of Veterinary Medicine

Anemia means a decreased number of red blood cells in circulation. Packed Cell Volume (PCV, also often called hematocrit) is the most common way to measure anemia and refers to the percentage of blood volume that is taken up by red blood cells. The normal PCV for a cat is 25-45%, and any PCV below 25% is considered anemic. 

Red blood cells carry oxygen and nutrients to the body’s tissues. These cells circulate for about 70-80 days before being removed from circulation and replaced with new red blood cells from the bone marrow. Without enough red blood cells in circulation, cells will not receive enough oxygen or nutrients to survive, so anemia can become a critical or even fatal situation very quickly.

Clinical Signs

Because anemia starves the body of oxygen (the body’s fuel), the first sign is often lethargy. An anemic cat may have little energy to play or may sleep more than usual. The cat’s gums may appear almost white or even yellow (a condition called jaundice) due to red blood cell destruction. In extreme cases, the cat may have trouble breathing, and respiratory and heart rates can increase as the body tries to compensate for the lowered oxygen delivery by the red blood cells.

Depending on the cause of anemia, fever and loss of appetite may occur due to an infection or inflammatory response. Black stools can be seen if blood loss occurs in the stomach or intestinal tract, and discolored urine can be a sign of red blood cell destruction. The signs of anemia can be very vague, however, and if a cat has been anemic for a long time, their body has likely had time to compensate and the cat may show no signs at home.

Causes of Anemia

There are many causes of anemia in the cat, but they can be broken down into three major categories: loss of red blood cells, destruction of red blood cells, and failure to produce new red blood cells. A discussion of some, but not all of the common causes of anemia from each of those categories is provided below.  Feline anemia is common and can be secondary to many health conditions.

Loss of red blood cells

Loss of red blood cells (hemorrhage) can be due to an obvious source such as a wound or trauma, or from more insidious causes. Flea and tick infestations are a major cause of anemia, especially in kittens, as the parasites suck blood from the body faster than it can be replaced.  The hookworm parasite (Ancylostoma tubaeforme), which feeds on blood in the intestines, can cause anemia in cases of severe infestation. 

Hemorrhage can also occur in the stomach or intestines due to ulcers or inflammation in the gastrointestinal tract. Cats with blood loss in these areas may have chronic vomiting, diarrhea, or black stools.

Reticulocytes are a specific type of red blood cell made and released by the bone marrow when it senses anemia in an attempt to compensate for the low red blood cell numbers. With chronic blood loss through the intestinal tract or from parasites, cats would be expected to show an elevated reticulocyte count. When a cat has a low red blood cell count and high reticulocyte count, this is called a “regenerative” anemia, as the body is reacting appropriately to blood loss. As long as red blood cells are being lost faster than reticulocytes can be released from the bone marrow, however, the cat will remain anemic.

Destruction of red blood cells

Red blood cells that have reached the end of their lifespan (about 70-80 days) are routinely removed from circulation by a cat’s body and replaced by new red blood cells made in the bone marrow. However, certain diseases can cause red blood cells to be broken down or destroyed more quickly than normal, leading to anemia as they are removed more quickly than they can be replaced.

Certain infectious diseases can lead to damage and destruction of red blood cells. These include Mycoplasma haemofelis, Candidatus, Mycoplasma haemominutum, Cytauxzoon felis, and Babesia species infections. These diseases are spread to cats by fleas and ticks, and they then attach to red blood cells, leading to their destruction.

Red blood cells can also be damaged by certain toxins. Oxidative injury to red blood cells secondary to the ingestion of acetaminophen (Tylenol ®), zinc, copper, onions, and some other toxins or medications can lead to anemia in cats.

Occasionally, a cat’s body tags its own red blood cells as foreign, causing them to be destroyed by the cat’s own immune system. This is called Immune-mediated hemolytic anemia (often abbreviated to IMHA). In some cases, there is a trigger causing the immune system to incorrectly destroy too many red blood cells. This trigger can include a reaction to a drug, cancer, or infectious diseases such as Feline Leukemia Virus (FeLV) or feline infectious peritonitis (FIP). If there no underlying cause for the inappropriate activation of the immune system is identified, this disease is called primary IMHA. There is no evidence that this is a hereditary disease in cats.

Anemias caused by loss or destruction of red blood cells are typically regenerative, so an elevated reticulocyte count would be expected as the body tries to compensate for the destruction of red blood cells.

Failure to produce red blood cells

New red blood cells are produced in the bone marrow to replace those that are regularly removed from circulation. A hormone produced in the kidney, called erythropoietin, is the primary signal that tells the bone marrow that more red blood cells are needed in the body. If the bone marrow is not able to produce enough red blood cells to replace those that normally outlive their lifespan, a cat will develop a non-regenerative anemia, with a low reticulocyte count.

One common cause of non-regenerative anemia in cats is chronic kidney disease. Chronic kidney disease is a very common, affecting approximately 15-30% of geriatric cats. When the cells in the kidney degenerate, they release less erythropoietin, leading to lowered red blood cell production by the bone marrow. As chronic kidney disease advances, 30-65% of affected cats will develop some degree of anemia.

Problems within the bone marrow itself can also lead to decreased production of red blood cells. Cancer, immune-mediated disease, or inflammation in the bone marrow can reduce its ability to replace red blood cells. Chronic inflammation elsewhere in the body can also impair the ability of the bone marrow to effectively produce red blood cells. This is often referred to as “anemia of chronic disease”, and can be seen with many other illnesses in cats, including FeLV infections and various cancers.

Diagnosis

The first step in diagnosing anemia is to determine the packed cell volume, or PCV. This test involves spinning down a small blood sample in a centrifuge to determine what percentage of the overall blood volume is made up of red blood cells. Further blood testing can look for evidence of regeneration in the red blood cells, abnormalities in other blood cell types such as white blood cells and platelets, evidence of organ damage such as chronic kidney disease, or the presence of infectious diseases.

Other tests, such as radiographs (x-rays) or an ultrasound to look for causes of bleeding or a bone marrow biopsy, may be recommended by a veterinarian,

Treatment

Treatment for anemia will vary depending on the underlying cause. In some cases, treatment for parasites or infectious diseases will be most important to stop the loss or destruction of red blood cells. Medications can be used to help stop bleeding from the gastrointestinal tract, and steroids and other immune-modulating drugs are essential in the treatment of immune-mediated diseases.

In cases of severe anemia, a blood transfusion may be necessary to replace red blood cells that have been lost or destroyed while the underlying condition is being treated. Cats have two major blood types, so it is important that both the donor and recipient blood be tested to reduce the risk of any reactions to the blood transfusion. 

In the case of chronic kidney disease, a medication called darbepoetin is available to help stimulate the production of new red blood cells in the bone marrow by replacing erythropoietin normally made in the kidneys. This medication requires weekly injections and close monitoring for side effects, but can result in resolution of anemia in 60-65% of cats with chronic kidney disease.

Last updated 2021

Hematocrit (HCT) / Packed Cell Volume (PCV) – Lab Results explained

Hematocrit is the percentage of red cells in your blood. 

Normal levels of hematocrit for men range from 41% to 50%. 

Normal level for women is 36% to 48%.  

What is hematocrit?

The hematocrit level is simply the percentage of red cells in your blood. For example, a level of 38% is considered the minimum needed for donating blood.

Hematocrit is the percentage by volume of red cells in your blood. Blood is made up of red blood cells, white blood cells and platelets, suspended in plasma. Together, those comprise about 45% of the volume of our blood, but the specific percentages of each can vary.

The importance of hematocrit:

Hematocrit is a significant measurement as it can identify whether you have sufficient red blood cells for oxygen transportation and delivery.

Hematocrit is important because red blood cells are essential to your survival. They contain a vital protein component called hemoglobin that binds to oxygen, which fuels all the cells in your body. When red blood cells pass through your lungs, they bind to and transport oxygen to various cells in your body. On their way back to your lungs, they carry carbon dioxide to be exhaled.

Why is the hematocrit test performed?

The hematocrit test checks for anemia, usually along with a hemoglobin test or as part of a complete blood count (CBC). This test can screen for, diagnose, or monitor many conditions and diseases that affect the blood’s proportion made up of red blood cells (RBCs).

What is a normal hematocrit level?

Normal hematocrit levels vary based on age and race, gender, etc.

In adults, normal levels for men range from 41%-50%. For women, the normal range is slightly lower: 36%-44%.  A hematocrit level below the normal range, meaning the person has too few red blood cells, is called anemia. A hematocrit level above the normal range, meaning too many red blood cells, may indicate polycythemia or erythrocytosis.

What are symptoms of anemia?

Symptoms of anemia include fatigue, shortness of breath and dizziness.

What are symptoms of polycythemia?

Symptoms of polycythemia include fatigue, itching, headaches, and sweating.

What are symptoms of erythrocytosis?

Symptoms of erythrocytosis includes headaches, dizziness, shortness of breath, and nosebleeds.

What is the difference between a hematocrit and a hemoglobin test?

Hematocrit is the percentage of red blood cells in your blood. Hemoglobin is a part of your red blood cell. Hemoglobin helps your red blood cells carry oxygen throughout your body. Hemoglobin also gives your red blood cells their color. A hemoglobin test measures the amount of hemoglobin in your red blood cells.

What is the origin of the word “hematocrit”?

The term “hematocrit” (british english: haematocrit) originated from the ancient greek word haimas (= blood) and krites (= judge) and hematocrit means “to separate blood”.

What does it mean if your Hematocrit (HCT) / Packed Cell Volume (PCV) result is too low?

Look for Possible Connected Biomarkers:  Low hematocrit + low RBC count + low hemoglobin indicates anemia. 

Anemia is usually defined as a decrease in red blood cells (RBCs) or hemoglobin in the blood. It can also be defined as a lowered ability of the blood to carry oxygen. 

Some causes of low hematocrit include:

– Nutritional deficiencies such as iron, folate, or B12 deficiency.

– Chronic inflammatory diseases or conditions.

– Excessive loss of blood from, for example, severe trauma, or chronic bleeding from sites such as the digestive tract (e. g., ulcers, polyps, colon cancer), the bladder or uterus (in women, heavy menstrual bleeding, for example).

– Damage to the bone marrow from, for example, a toxin, radiation or chemotherapy, infection, or drugs.

– Bone marrow disorders such as aplastic anemia, myelodysplastic syndrome, or cancers such as leukemia, lymphoma, multiple myeloma, or other cancers spread to the marrow.

-Kidney failure—severe and chronic kidney diseases lead to decreased erythropoietin production, a hormone produced by the kidneys that stimulate RBC production by the bone marrow.

– Decreased production of hemoglobin (e.g., thalassemia)

– Excessive destruction of red blood cells. That is caused by autoimmunity or defects in the red blood cell itself. For example, hemolytic anemia.

What does it mean if your Hematocrit (HCT) / Packed Cell Volume (PCV) result is too high?

Look for Possible Connected Biomarkers: A high hematocrit alongside with a high RBC count and high hemoglobin indicates polycythemia.  

Polycythemia (also known as polycythaemia or polyglobulia) is a disease state in which the proportion of blood volume occupied by red blood cells increases. 

Some causes of a high hematocrit include:

– Dehydration—this is the most common cause of a high hematocrit. As the volume of fluid in the blood drops, the RBCs per volume of fluid artificially rises; with adequate fluid intake, the hematocrit returns to normal.

– Living at high altitudes (a compensation for decreased oxygen in the air)

– Smoking

– Lung (pulmonary) disease—if someone cannot breathe in and absorb sufficient oxygen, the body tries to compensate by producing more red blood cells.

– Congenital heart disease—in some forms, there is an abnormal connection between the two sides of the heart, leading to reduced oxygen levels in the blood. The body tries to compensate by producing more red blood cells.

– Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)

– Kidney tumor that produces excess erythropoietin

– Polycythemia vera—a rare disease in which the body produces excess RBCs inappropriately.

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Universal Veterinary Clinic, CBC

CBC is a test profile used to describe the quantity and quality of cellular elements in blood and plasma. Most often, in daily practice, this is the first step to assess the condition of the animal. The organism of our patients is exposed to various environmental factors and gives a specific assessment for stimuli. When the indicators of clinical analysis change, we can talk about the possible cause of the disease.

Main indicators of clinical blood analysis:

1) Hemoglobin (HGB) is a pigment contained in red blood cells, whose function is to transport oxygen and carbon dioxide through the vessels. Its determination in the blood is not only of diagnostic value, it is also important from the point of view of disease prognosis, since pathological conditions that lead to a decrease in the content of this indicator lead to oxygen starvation of tissues.

2) Hematocrit (Ht, HCT) – the volume of red blood cells in the blood. An increase in this indicator may indicate erythrocytosis (an increase in the number of red blood cells), dehydration, or a decrease in the volume of circulating plasma.
A decrease in hematocrit indicates severe anemia. Low hematocrit is also characteristic of chronic inflammation, injury, starvation, chronic kidney disease, and cancer.

3) Erythrocytes ( RBC ) – red blood cells containing hemoglobin. The main functions are the transport of oxygen from the lungs to the tissues of the body and the transport of carbon dioxide from the organs to the lungs.

4) Leukocytes ( WBC ) – “white” blood cells with a nucleus. Their main function is to protect the body from various pathological agents, as well as internal pathological processes that are accompanied by inflammation.

Leukocytes are divided into two fractions: granulocytes (neutrophils, basophils, eosinophils) and agranulocytes (lymphocytes and monocytes). Their ratio in the blood plays an important diagnostic role, so their number is described in leukocyte formula .

5) Platelets ( PLT ) – elements responsible for the integrity of blood vessels play an important role in the regeneration and healing of damaged tissues.

A 12-hour fasting diet is recommended for CBC. Blood is taken from peripheral veins in a volume of about 2 ml (depending on the tube). It is carefully mixed and sent to the laboratory at a temperature of + 2 … + 8 degrees Celsius. In our center, the blood immediately goes to the laboratory, where within 5 minutes it is examined on the ProCyte Dx clinical analyzer (IDEXX company), which is currently the “gold standard” of automatic clinical analyzers.

Deciphering the general clinical blood test is carried out only by a veterinarian.

We wish you and your pets good health.

Reticulocytes (blood level determination)

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Reticulocytes are the immediate precursors of mature erythrocytes; the indicator reflects the production of erythrocytes in the red bone marrow (assessment of erythropoiesis).