Labwork Part 2 – The Complete Blood Count
This week I’m going to cover the complete blood count. The post will be divided into pages, so just click the numbers at the bottom to move to the next page!
We need to start out with an explanation of the components of blood so that we can understand what is being counted. I’m going to try to draw an imperfect analogy to cooking (or at least to a recipe) to help.
Blood is soup. It’s composed of a liquid portion — the broth — which contains water, salts (electrolytes), small proteins, and antibodies. The chunks in this particular soup are cells of various types. These cells are produced in the bone marrow from larger, more complex progenitor cells. Through a series of divisions, these larger cells are transformed into red blood cells, white blood cells, and platelets. I suppose you could consider these the vegetables in the soup. Each cell type has a specific function in the body. The forms of the cells are specialized to handle these functions. The donut-cell on the left is a Red Blood Cell. The little spiny thing in the middle is a Platelet. And the fuzzy ball on the right is a White Blood Cell. This is a scanning electron microscope picture.
When we draw blood, part of the sample is put into the purple top tube. This tube prevents the blood from clotting. When we send this sample to the lab, they do two types of analysis on it.
The first is to run the blood through a special counting machine. Usually, this machine uses a laser to shine light through the cells as they pass through a very tiny tube. The effect the cells have on the light is recorded by the machine. Because the composition of the cell types differs, the machine is able to tell which type of cell has just gone through the tube. It keeps track of this and gives us a count of each type of cell. Before we had the technology to count cells with a machine, a trained individual had to look at the sample through a microscope and count the different cell types by hand. This is a picture of the laser cell concept:
The next test that’s done on the blood is to take a drop of blood and spread it in a very thin layer on a microscope slide. This is called a blood smear. The smear is dipped in special stains to color the cells. This staining allows us to distinguish parts of the cells as well as the types of the cells more readily. In some cases, we can also identify abnormalities with the structure of the cells. This visual pathology review is still done by humans. Here is a picture of how to make a blood smear, and then a picture of what it looks like under the microscope. Notice the different types of cells that can be seen there — they differ in size, shape, and color.