Why is rbc test done

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The red blood cell RBC count is a test used to measure the number of oxygen-carrying blood cells in a volume of blood. It is one of the main tests doctors use to determine how much oxygen is being transported to cells of the body. An abnormal RBC count is often the first sign of an illness.

At other times, the test can point the doctor in the direction of a diagnosis if there are symptoms like unexplained fatigue or shortness of breath.

Keep reading to learn more about your red blood cell count and what it means if it's too low or too high. Usually, the doctor needs to look at more than an RBC count to diagnose a medical condition. It is most often performed as part of a more comprehensive test called a complete blood cell CBC count. This test measures several different components of a blood sample, including:.

Based on the composition of the blood, doctors can have a better idea of what to look for when trying to diagnose a medical condition. This is especially true for cancer and chemotherapy. Both of them can negatively affect blood counts. An RBC count is the number of red blood cells per a particular volume of blood. It may be reported in millions of cells per microliter mcL of blood or in trillions of cells per liter L of blood.

The "normal" or "reference" range can sometimes vary depending on whose blood is being tested. If you live in a high-altitude city like Denver, your blood count will be far higher than people who live in low-altitude areas like the Gulf Coast. This is because when you are at a higher altitude, your body creates more red blood cells so that more oxygen can be carried to your tissues.

For this reason, the ranges cannot be considered hard-and-fast values but just a reference point. When the RBC count is higher or lower than the average range, it alerts the doctor that a medical condition could be the cause. The other values from the CBC will be considered, as well as other diagnostic tests.

A high RBC count tells us that there has been an increase in oxygen-carrying cells in the blood. In some cases, this may reveal that the body is trying to make up for some condition that is preventing the body from receiving enough oxygen.

In others, the cause may be related to diseases or drugs that increase the production of RBCs. Some of these causes include:. A low RBC count shows there is a decrease in oxygen-carrying cells in the blood. These include white blood cells, hemoglobin level, and platelets. If your healthcare provider suspects you have a particular illness, they may also order other tests needed for making a diagnosis. Test results may vary depending on your age, gender, health history, the method used for the test, and other things.

Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. Normal values may vary slightly among different labs. One example of normal values is:. An RBC count that's lower than normal can be a sign of many health problems, including:. An RBC count that is higher than normal can be a sign of many health problems, including:. The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Having a blood test with a needle carries some risks. Back to Health A to Z. A red blood cell RBC count is a blood test that tells you how many red blood cells you have.

The amount of oxygen that's delivered to your body's tissues depends on the number of red blood cells you have and how well they work. Women usually have a lower RBC count than men, and the level of red blood cells tends to decrease with age.