PCV & TP

One of the most commonly used and simplest blood tests in veterinary medicine is the packed cell volume.

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Also known as the PCV or the hematocrit, the PCV measures the percentage of red blood cells to the total blood volume.  Blood is placed into a small hematocrit tube.  One side is sealed in clay. Next the tubes are placed in the centrifuge (clay must be facing the outside) and spun for about three minutes.  This spinning separates the different layers of the blood, depending on each components density. At the bottom are the red blood cells.  At the top is the plasma, which mostly made up of water with dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide.  Separating these two layers is the buffy coat, which contains the white blood cells and platelets.

There are several different things that you can tell about the health of a patient, just by looking at the results of the PCV.  Firstly, and most importantly, you can determine if the blood contains a normal amount of red blood cells.  The normal percentage of red blood cells would be around 40% - 45%.  If the red blood cell count is extremely high, it could mean that the animal is dehydrated and needs fluids pronto!  If the red blood cell count is extremely low, it could mean that the animal is anemic.

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Anemia is a condition of the body where the body does not have enough hemoglobin.  Hemoglobin is the protein in red blood cells that bonds to oxygen and carries it to the body tissues.  If there are low levels of red blood cells with hemoglobin, the amount of oxygen reaching the organs is not going to be enough to sustain them for very long.   Anemic patients can be spotted very quickly, even before running the PCV though.  Doctors will usually check animal's gums to see if they still have that pinkish tint.  If their gums are white, it is a sign that they are anemic. 

Sometimes the plasma has a yellowish color, meaning that the animal is icteric.  Icterus is not a good diagnosis; there are three causes to Icterus, including hemolysis (the destruction of red blood cells), liver disease, or an obstruction in the bile duct.  With this information, several different diagnoses are considered and usually more blood work is done to narrow the possibilities down. 

Another test that we do once the PCV has been measured is to measure the total proteins within the blood sample.  The hematocrit tubes are cracked right at the beginning of the plasma and the plasma is tapped onto a protein refractometer.  Next, you hold the refractometer up towards the light and measure the amount of total proteins on the scale.

Total proteins is an important test to run because it tells you the amount of all the proteins flowing in the fluid portion of the blood.  The total protein test is important in telling you whether the patient might have nutritional problems, kidney disease, or liver disease.  The normal range of total proteins falls between 6 - 8.3 gm/dl (grams per decaliter).  If the test shows higher than normal levels of proteins, this may be a sign of chronic inflammation or infection or a myeloma.  If the tests show lower than normal levels of protein, this may be a sign of malnutrition, a hemorrhage, malabsorption, or liver disease.