Anemia in Animals, Part 2—Physiology of the Red Blood Cell (RBC) • Long Beach Post

By Carl Palazzolo, DVM, Long Beach Animal Hospital (LBAH) 

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Photos courtesy of LBAH.

Last week, Dr. Palazzolo gave us an anatomy of the red blood cell. This article, part 2 of a series on anemia in pets, will tell us about how the blood cells are processed and how veterinarians examine them.

As RBCs flow into the lungs, the iron in the hemoglobin molecule in the RBC absorbs oxygen. With this fresh supply of oxygen, the RBCs flow from the heart through progressively smaller blood vessels. This flow starts with large arteries, continues to small arteries, and progressing to even smaller arteries called arterioles.

Eventually, the RBCs flow into capillaries. These are the very small blood vessels that surround each individual cell in an organ. It is at this point in the cardiovascular system that the RBCs do their magic.

RBCs have a biconcave shape, allowing them to compress and bend as they flow through the tiny capillaries that surround the cells. This compressibility is important. Some capillaries are so tiny that they are even smaller than the diameter of the red blood cell. For the red blood cell to squeeze through the capillary, it needs to be able to compress its shape.

When RBCs finally arrive at a cell, the oxygen attached to hemoglobin passes through the wall of the RBC and through the wall of the cell. At the same time, some of the carbon dioxide in the cells passes through the cell wall and RBC wall, eventually attaching itself to the hemoglobin molecule. Once this has occurred, off the RBC goes to the lungs to exhale the carbon dioxide and absorb more oxygen, to be delivered to another cell somewhere in the body.


This is the tiny blood tube after blood has been obtained. This is a great way to check for and monitor anemia in sick pets and small pets, since only a few drops of blood are needed to fill this tiny tube. Clay is put in the bottom so the blood does not flow out of the tube into the centrifuge.


A special centrifuge is needed for this test.


After we check the percentage, we break the tube in half.


We place the serum from the tube on a special instrument called a refractometer to determine the protein level in the serum, another important test to determine health.

It takes an awful lot of RBCs to supply the trillions of cells of the average mammal with this oxygen-delivery-and-carbon-dioxide-removal system. A typical dog or cat has up to 10 million RBCs in a cubic centimeter (cc). That means that one teaspoonful of blood can contain up to 50 million red blood cells! It’s a phenomenal number, one that is beyond human comprehension. It’s a miracle that it works at all, which is why sometimes the system breaks down.

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When a blood sample is taken and put into a tube, there is a mixture of red blood cells and plasma. The plasma contains clotting factors and other nutrients that flow through the blood stream. When you spin a blood tube down in a special tube and centrifuge, the plasma and red blood cells separate. Almost half of it is red blood cells (lower white arrow). The other half is serum (top arrow). This is the sample we send to the lab to do a vast array of tests on the serum, called the biochemistry panel.


We can do a quick in-house check of the red-blood-cells percentage without sending it to the lab. This is called a “hematocrit (HCT).” A tiny blood tube is filled up and spun down to let us measure the percentage of red blood cells. Depending on the species, age and disease process, we want to see it in the 30s and 40s. This pet has an HCT of 37%, so it is not anemic.

Next week, I will talk about how we diagnose anemia.

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