Complete Blood Count (CBC)

[Jeff]

Special thanks to the Author: Patricia Gail Burnham and Dog World Magazine for permission to post this very informative article. This article was published in the March 2000 issue of Dog World http://www.dogworldmag.com

 

The Meaning of a Complete Blood Count (CBC)

Patricia Gail Burnham

General blood tests performed for dogs can be divided into two kinds: chemistry profiles and a CBC (Complete Blood Count).  The chemistry profile measures various chemicals in the blood while the CBC counts the various types of red and white blood cells.  Living blood cells make up 45% of blood.  The blood cells are swimming (or floating depending on the type) in blood plasma that makes up the other 55% of blood.

Complete Blood Count (CBC).  A complete blood count is just that, a count of the various living cells that are swimming around in the blood serum.   They are divided into two basic types of cell: red blood cells and white blood cells.  All of the cells in the blood are produced in the dog’s bone marrow.

Red Blood Count (RBC) Red blood cells make up 99% of the total blood cells.  Red cells are the longest-lived blood cells, living as long as four months.  The job of the red blood cells is to carry oxygen from the lungs to the cells, and the dog needs oxygen all the time so the demand for red cells is ever present.  (If you are a blood donor, the reason that you are only allowed to donate a pint of blood every six weeks is that it takes that much time for your bone marrow to replace the red blood cells that were given in your donation.  If you donate blood plasma your body will replace the donation in two weeks, while it will replace donated platelets within three days.  It is the red cells that take the longest to replace.)  

Poor oxygenation of the blood will cause the liver to produce excess hemoglobin and the bone marrow to produce more red blood cells.   High red counts are produced by dehydration, polycythemia (an excess of red cells being produced), bone marrow disease, excess iron, or malfunctioning of the liver or spleen.  A low red count can be caused by either nutritional or genetic anemia.  Nutritionally, iron, B12, and folic acid are required to manufacture red blood cells.

$        Normal Adult Range 4.8-9.3 million/UL

Hemoglobin ( HGB)  Hemoglobin is the oxygen carrying protein in the blood.  If  the HGB level is high, then some toxin or a low oxygen level is stimulating the liver to produce extra hemoglobin, or the liver or spleen are not functioning, or excess iron is being consumed.  A low hemoglobin level is caused by anemia due to lack of iron, B12, or folic acid in the diet.

$        Normal Adult Range 12.1-20.3 G/DL

 

Hematocrit (HCT)  The hematocrit is a measure of the percentage of the red blood cells in the blood.  A high HCT indicates dehydration or a reduced breakdown of red blood cells by the spleen.  A low HCT indicates anemia, or an overactive spleen, or over hydration.

$        Normal Adult Range 37-55%

Mean Corpuscular Volume (MCV).    The MCV  reflects the size of the red blood cells. MCV is a calculated value that uses the volume of a red cell divided by the total number of red cells.  If the level is high it means the red blood cells are larger than normal because they are old cells that the spleen has not destroyed. Iron deficiency anemia is a macrocytic (large cell) anemia because even though there are fewer red blood cells produced, each one is larger than normal.  A dog’s MCV is high in iron deficiency anemia.  Conversely, anemias due to B12 or folic acid deficiency are microcytic (small cell) anemias because the red blood cells are smaller than normal.  If the MCV is low, the red blood cells are small and young and oxygen will not be transported efficiently to the tissues.

$        Normal Adult Range 58-79 FL

Mean Corpuscular Hemoglobin( MCH)  MCH gives the average weight of the hemoglobin in the red blood cells.  MCH is calculated by dividing the HGB by the RBC.  If the level is elevated it means inadequate oxygenation.  If the level is low, the red blood cells are pale, usually due to an iron deficient diet.

$        Normal Adult Range 19-28 pico gms

MCHC (Mean Corpuscular Hemoglobin Concentration)  MCHC tells if the average red blood cell is anemic. MCHC is calculated by dividing the MCH by the MCV.   A low MCHC indicates hypochromic anemia.

$        Normal Adult Range 30-38%

White Blood Count (WBC):  The white blood cells are your dog’s disease fighting cells.  Most of us have seen education films of magnified white cells attacking, killing and eating invading bacteria.  White cells are some of the world’s smallest predators.  They act as the dog’s defense army against invading microbes.  The white blood cell count measures the disease fighting abilities of the blood.   White blood cells in a healthy dog only account for one percent of the blood cells.  They are far outnumbered by the oxygen carrying red cells.   Because white cells are used only when it is necessary to fight an infection or disease, there is no reason to have hordes of them circulating in the blood of a healthy animal.  Instead, small numbers of white cells circulate to meet the initial infection, but  the body is capable of producing a large number of white cells quickly when they are needed to fight an infection or disease.   So a high WBC indicates a that the body is producing white cells to meet the attack of a bacterial infection.  A lower than normal level of white cells indicates a weak immune system, an active disease or a current infection that is winning its war with the white cells.

$        Normal Adult Range 4.0-15.5 thousands/UV

In addition to the total white blood count, the blood count will give a breakdown of the percentages of four different types of white cells.   All white cells start out as blasts.  They mature through stages into a variety of types of white cells.  These are the neutrophils, lymphocytes, monocytes and eosinophils.   The readings for the different types of white cells are given both as an absolute figure and as percentages of the total white count.  The percentages for the four types of white cells should add up to 100%

Neutrophils are short-lived blood cells.  The only live for seven hours, during which time they help combat infections.    They are also called granulocytes.  They start out as blasts and mature through several stages from blast to myleocyte to metamyelocyte to a segmented neutrophil.  At one stage in their development they start showing characteristic dark granules in their nucleus which is why they are called granulocytes.

$        Normal Adult Range 60-77 % (2060-10600/UL)

Lymphocytes are white cells that help fight infection.  T-cells are lymphocytes under the control of the thymus gland.  T-cells alert the body to germs, viruses, and toxins. B-cells manufacture antibodies. If the lymphocyte level is elevated,  the immune system is active due to an infection.  If the count is very low, the immune system is exhausted.

 

$        Normal Adult Range 12-30 % (690-4500/UL)

Monocytes are part of the mononuclear group of cells that help the granulocytes fight infection.  An elevated level indicates chronic degenerative diseases including liver infection.  In this case you want a low value.

$        Normal Adult Range   3-10% (0-840/UL)

Esinophils are cells in the granulocytic series.  Esinophils got their name because they stain red with a dye called eosin.  The eosinophils protect against allergic reactions and parasites.  If elevated, an allergy is in progress or parasites are present.

$        Normal Adult Range 2-10% (38-1200/UL)

Platelets.  Large cells within the bone marrow called megakaroyocytes, regularly pinch off pieces of their cytoplasm.  These cell fragments, which contain no nuclei, enter the bloodstream where they help blood to clot.  They are called platelets.  They live for a week.   My blood bank selectively harvests platelets to give to cancer and burn victims.  The plastic platelet bags are air permeable to let the live cells breathe .  A bag full of platelets doesn’t look like blood at all.  It looks like pale yellow melted fat.  But without platelets, blood won’t clot.  A raised platelet level indicates dehydration or over active bone marrow.  A low level can be caused by drugs, an immune system failure, or low B12 or folic acid intake.  Chemotherapy and burns will also lower platlet levels.  A very low level is considered to be life threatening, as a dog could bleed to death internally.

.$        Normal Adult Range 170-400 thousands/UL

There are some breeds of dogs for which the normal range of blood cell counts is different from the averages.  Greyhounds, because of their specialization for high speed running, tend to have higher red cell counts both at rest and when running, and they often have borderline low white counts.   For example a normal resting red count range for Greyhounds is 7.8-9.2 million /UL .   This is on the high end of normal for the average dog and has led some veterinarians to treat normal Greyhounds for polycythemia when their red blood counts are within normal for Greyhounds.

You can’t just add extra red cells to blood without risking making the blood so thick that it won’t pump properly, so in order to raise their red cell count, Greyhounds have lowered their white counts.  For the improved running speed that extra red cells provide, Greyhounds have been bred to maximize their oxygen carrying red cell counts and minimize their white cell counts. A healthy Greyhound’s white count ranges from  3.5 to 6.5 thousand/UL, which would be low for a normal dog.   While extensive research has been done on Greyhounds because of their racing activities, it is possible that the other sighthound breeds might also differ somewhat from the normal values for red and white cell counts.