Your Blood: Everything Counts in the Right Amounts

12/12/2003

By Christine Haran

Most of us know that when we go to our healthcare provider with a physical complaint or for a check-up there is a good chance we will be prodded with a needle. Once the blood is drawn, the doctor usually has a lab do a CBC, or complete blood count.

One of the reasons the CBC is such a popular test is that it screens for many different kinds of medical problems by measuring types of blood cells and other components of the blood. It's also used to monitor blood counts when people are taking certain medications that affect the blood, or have blood-related conditions.

Below, Anthony Kurec, administrator for the University Pathology Laboratory at SUNY Upstate Medical University in Syracuse, explains what CBCs measure and what they tell patients and doctors about patients' health.

What is a CBC?

The CBC measures the number of blood cells and related components in circulating blood. Specifically, the CBC measures the number of red blood cells, white blood cells, and platelets present in the peripheral blood, which is the blood that travels through the veins and capillaries. They all have different functions, and in normal, healthy individuals, they are relatively constant in number.

It also measures the level of hemoglobin, which is a protein within the red blood cell that carries oxygen to tissues and the hematocrit, which is the percentage of red blood cells per total volume of blood, as well as several other measurements related to the red blood cells. These include MCV (mean corpuscular volume), which measures the average volume of the red blood cell; MCH (mean corpuscular hemoglobin), which measures the average amount of hemoglobin within that red blood cell; and MCHC (mean corpuscular hemoglobin concentration), the average percentage of hemoglobin in the red blood cell.

Why would you use this screening test?

It's probably one of the first tests that a doctor orders. What they are looking for depends on what your complaint is. A doctor might recommend a CBC because you have constant fatigue and might be anemic. It is often used to screen for any suspected disease or condition caused by dangerously abnormal changes in cells counts, such as the presence of certain cancers, exposure to certain chemicals, or infections. It's routinely used when you have a hematologic disease such as leukemia or lymphoma, or other blood-related or chronic illness.