How many red cells are there in human blood? How are they counted?

Red Blood Cells

The liquid part of our blood is called plasma. In the plasma, there are millions of tiny cells. Each of them is too small to be seen except under a microscope. Of these cells, the red ones are by far the most numerous.

In spite of their small size, it is still possible to figure out how many red cells there are in our blood. To do this scientists take a very small, measured quantity of blood and the red cells in it. From the figure they get, the scientists then make a projected calculation to estimate the number of red cells in the whole body.

To elaborate; an adult person has about five to six liters of blood. In a certain portion of blood, about the size of two pinheads (1 cubic millimeter), there are normally about five million red blood cells. The total number in the body is thus probably about thirty-five trillion.

Men ordinarily have a few more red cells than women, and a newborn baby has about one million more than a grown person. It is possible, by counting in the way described above, to determine whether a person has the proper number of red blood cells for health.

The RBC Test

It’s important to have the right amount of red blood cells if we want to have good health. A doctor can find out how many red cells we have by ordering an RBC (Red Blood Count) test. Red blood cells have hemoglobin, which is what passes oxygen along to our body tissues. Since tissues need this oxygen to survive and function properly, we need to make sure that we don’t have an abnormal count of red blood cells.

A doctor might order a CBC (Complete Blood Count) test when we go for a physical exam. This is a test that includes the RBC test, so we can find out the number of red cells we have in our blood from the results. Pregnant women and people with certain health conditions would probably have to take a CBC before their doctor will proceed with any treatment.


If our RBC is too low, there could be several complications and symptoms. These in clued getting short of breath very quickly, getting tired easily, a rapid heart rate, frequent headaches, vertigo, a feeling of weakness, and pale skin.

A low RBC count might be caused by several factors. These include bone marrow failure, anemia, bleeding (both external and internal), malnutrition, leukemia, pregnancy, thyroid disorders, etc. Some drugs might also reduce the RBC count, so these need to be ruled out by a doctor before starting any new medication.

High RBC

It’s also not good to have too many red blood cells in our system. The symptoms of a too-high count include disturbed sleep, itching skin especially after showering or bathing, tender palms or soles, and joint pain.

A high RBC count leads to a condition called erythrocytosis. The reason for this might be dehydration, cigarette smoke, kidney cancer, bone marrow disease, congenital heart disease, or pulmonary fibrosis. One’s RBC count will also increase if they travel to a higher altitude than usual. The increased count might last for some weeks due to the decreased oxygen they get with each breath.

Treating Abnormal Counts

While the causes of high or low RBC counts might seem alarming at first glance, it’s usually best not to jump to conclusions without the proper testing and diagnosis. Most of the time, an abnormal count is treatable and can even be dealt with through lifestyle changes.

In addition to starting any recommended medication, those with abnormal RBC counts can start making a few healthy changes in their way of life. Eating a healthy and balanced diet will help us avoid any vitamin or nutritional deficiencies. A bit of regular exercise will help the body use up the oxygen that the red cells provide, which is also healthy. It’s also a good idea to avoid taking aspirin and cut down on smoking as much as possible.

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