Reticulocytes

and Eva Rudolf-Müller, doctor

Dr. med. Andrea Reiter is a freelance writer for the medical editorial team.

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Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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Reticulocytes are young, immature red blood cells (erythrocytes). They are formed in the bone marrow and washed out into the blood. There they mature into mature cells within a few days. The percentage of reticulocytes in the blood is very small, but can increase if there is a lack of oxygen or after blood loss. Read when the bone marrow releases more reticulocytes and when their percentage in the blood is reduced!

What are reticulocytes?

Reticulocytes are red blood cells that are not yet fully mature. Like the mature erythrocytes, they no longer contain a cell nucleus, but still have certain genetic information (RNA) and the endoplasmic reticulum (Latin "rete" = network) in the cell plasma. The latter takes care of certain cell metabolism processes and gives the cell interior a typical reticulate appearance under the microscope. When RNA and endoplasmic reticulum have been expelled, the reticulocyte has matured into an erythrocyte.

The number of reticulocytes in the blood allows conclusions to be drawn about the blood formation activity of the bone marrow. It can indicate certain conditions such as anemia or infections. However, it also changes when there is a lack of oxygen in the air we breathe, for example at high altitudes. Doping to increase blood formation (e.g. with EPO) also changes the rate of blood formation.

When do you determine the reticulocytes?

The reticulocytes in the blood are determined in the following cases:

• if you are anemic (anemia)
• during therapy with iron, vitamin B12 or folic acid
• for a medically required therapy with erythropoietin (EPO)
• for blood cancer (leukemia)
• after a stem cell transplant

Reticulocyte counts

The measurement result of the reticulocyte determination is given in per mille (‰) of erythrocytes - i.e. the number of reticulocytes per 1,000 mature erythrocytes. The following standard values ​​apply depending on age and - for adults - depending on gender:

age	Reticulocyte normal range
1 to 3 days	34,7 - 54,0
4 to 30 days	10,6 - 23,7
31 to 60 days	21,2 - 34,7
61 to 180 days	15,5 - 27,0
0.5 to 1 year	9,90 - 18,2
2 to 5 years	8,20 - 14,5
6 to 11 years	9,80 - 19,4
12 to 17 years	9,00 - 14,9
from 18 years	female: 5.40 - 20.2 male: 4.80 - 16.4

When are there too few reticuloytes in the blood?

If there are not enough reticulocytes in the blood, blood formation could be reduced. Certain forms of anemia may be the cause (such as folic acid and vitamin B12 deficiency anemia or aplastic anemia). A deficiency in the hormone erythropoietin (important for blood formation) as well as radiation and chemotherapy (for cancer) can lower the reticulocyte values.

When are there too many reticulocytes in the blood?

If the number of reticulocytes is increased, this indicates increased blood formation. This can be a normal regulatory mechanism of the body: for example, the bone marrow produces more red blood cells after a heavy bleeding. Even if the bone marrow is damaged and is regenerating, the percentage of reticulocytes in the blood can temporarily increase. The same applies if preparations with iron, folic acid or vitamin B12 are taken in the event of anemia.

In addition, an increased proportion of reticulocytes in the blood can be the result of a chronic undersupply of oxygen (hypoxia) or an increased breakdown of red blood cells (hemolysis).

What to do if the reticulocyte count changes?

An increased proportion of reticulocytes in the blood is often just a countermeasure taken by the body, for example in the event of severe blood loss or anemia. If the proportion in the blood is high or persistently increased, it must be checked.

If the reticulocyte values ​​are changed and cannot be explained (e.g. with a loss of blood), the cause must be clarified. If it is caused by a disease such as leukemia or hypothyroidism, it must be treated accordingly.

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