Is that a happy face, or what? Plato was a good and cooperative patient. We and his family miss him so much.

Packed cell volume (PCV).

All of these terms mean the same thing: What percentage of a patient’s blood is red blood cells (RBCs)?

The pet at hand today is Plato, a cancer patient on chemotherapy who has a mass in one of his lungs. He has been bleeding, his respiratory rate has increased, his breathing has become more difficult and we suspect he may have some internal bleeding from that lung mass.

We know Plato doesn’t have much time left, but we want him to be as comfortable as possible. Knowing whether he has internal bleeding will help us determine his prognosis.

In a normal dog, PCV is between 36% and 60%. Cats’ normal range is between 29% and 48%.

Draw a tiny bit of blood, let the hematocrit tube pull it in by capillary action, then spin at 12,000 RPM. A scale gives the user the percentage of the blood that is red blood cells.

That figure is determined by taking a very small amount of blood and putting it into a microhematocrit tube, a thin piece of glass only a few millimeters wide and 75 mm long. One end is plugged with a special caulk and the tube is inserted into a machine called a centrifuge. The centrifuge spins at speeds up to 12,000 RPM, forcing the heavy red blood cells to the bottom of the tube, leaving the liquid portion of the blood on top.

After spinning, if half of the volume of the tube is packed red blood cells, and half is fluid (serum or plasma), the patient is said to have a hematocrit or PCV of 50%.

Lower-than-normal readings indicate anemia. Our next step would be to determine whether the cause is blood loss or failure to make new RBCs.

Higher-than-normal hematocrit can result from dehydration or overproduction of red blood cells. The latter is a condition called polycythemia.

Here, you can see that this patient’s blood is about 25% red blood cells, well below the minimum normal of 36% for dogs and 29% for cats.

Microhematocrit is a quick and inexpensive test that most veterinarians can run right in the office.

Sadly, we found Plato’s PCV to be low. He lasted only a couple more days.

We miss you, old friend.

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