What Is a Complete Blood Count for?

Medicine has developed and continues to create many different methods and technologies to reveal and get to know the complex machine that is our organism, not only in general but that of each individual and at each specific moment. One of these methods is analysis, including blood analysis.

Blood is a body tissue that appears to be a homogeneous liquid but is composed of several differentiated cell types, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. These would be the so-called formal elements of the blood, i.e., those with a definite shape and contour. In addition to these cells, the blood contains plasma; it’s a liquid part containing water, proteins, mineral salts, and other substances. It is used to transport oxygen and nutrients to all the cells of the organism and other elements such as hormones, minerals, vitamins, etc.

The most common determinations performed in blood tests are hemograms, coagulation, biochemistry, and blood gases.

You may not like going to the doctor; you may be afraid of needles or even see how the blood accumulates in those tiny tubes that the nursing staff takes out of the blood culture collection kits. But if there is one thing you can be sure of, it is that sooner or later, for whatever reason, you will have to go for a complete blood count.

A CBC or hemocytometer is a test that consists of a complete blood cell count and an assessment of the typical structure and shape of blood cells from a small sample of blood. In the past, it was an arduous process because the count was performed manually, observing the microscope. Still, nowadays, automated hemograms allow knowing with comfort, speed, and accuracy results. 

The blood test is the first of the examinations requested by the physician for the patient who comes to the doctor’s office for a health problem. A blood test can have different purposes:

The primary purpose is to confirm or rule out a disease or health problem suspected by the physician based on the signs and symptoms presented by the person who comes to consultation.

It is also used to determine how a patient is progressing with any alteration or disease and is receiving treatment. 

Another everyday use of blood tests is as part of periodic check-ups or check-ups aimed at monitoring the state of health of a person and the early detection of diseases.

Generally, a hemogram is performed to measure the concentration of red blood cells, white blood cells, leukocytes, and platelets, in addition to checking whether the cells have a regular shape and structure. On the other hand, biochemistry analyzes the chemical substances present in the blood, such as sodium, potassium, calcium, glucose levels, urea, creatinine, cholesterol, iron, vitamins, enzymes, folic acid, and liver enzymes. An abnormal amount of any of the cells may be indicative of disease.

If you have a blood test, a sample will be drawn. The blood volume to be removed will depend on the number of tests your physician has ordered but is unlikely to exceed 50 mL (cubic centimeters).

In most cases, the blood is taken from a vein, usually from the elbow area, but some tests, such as blood gas analysis, must be performed with arterial blood. 

Before the puncture is performed, a tight rubber band will be placed around your arm to highlight the vein. This maneuver helps the health personnel to perform the puncture more safely and with minor discomfort for you. Next, they will open one of the blood culture collection kits and clean the puncture site with alcohol, insert the needle attached to a blood collection device into the vein or artery from which the sample will be obtained, and remove the rubber band to allow the blood to flow smoothly. Once a sufficient sample has been received, the needle will be removed, and you will be asked to press with a cotton ball on the puncture site with your elbow bent for a few minutes to avoid bruising.