Generality
Reticulocytes are not yet mature red blood cells . As a result, the reticulocyte count is the main indicator of the amount of red blood cell production.
This analysis is important for assessing bone marrow function and its ability to produce an adequate number of erythrocytes (synonymous with red blood cells).
What's this
Reticulocytes are the transition elements between nucleated erythroblasts (proeritroblasts) and red blood cells. These cells of the erythroid line are produced in the bone marrow and, when they are released into the bloodstream, they take on the specific characteristics of the erythrocyte, after about a day of maturation (note: the whole process of differentiation lasts 10 days).
The reticulocytes are defined by the presence of cytoplasmic material, consisting mainly of mitochondria and residues of genetic material (ribosomal ribonucleic acid), which can be highlighted as granules and filaments with an excess color, such as the cresyl bright blue.
Red blood cells survive in circulation around 120 days; consequently, the bone marrow is continuously engaged in the production of new erythrocytes, which go to replace the old or degraded ones. In this way, a constant number of red blood cells is always maintained in the blood.
The absolute or percentage reticulocyte count is a good indicator of a person's bone marrow capacity to produce red blood cells (erythropoiesis).
Reticulocytes: biological role and normal values
In the adult about 2 million red blood cells are produced per second. During cell maturation, there is a stage in which the nucleus is expelled, and which lasts 1-2 days. This stage corresponds to the reticulocyte; it will then become mature erythrocyte (which will have a life of about 120 days). Thus, reticulocytes are young, still immature red blood cells, and are 0.5% - 2.5% of circulating red blood cells. For example, in a subject that has 5 million red blood cells per μl, the reticulocytes will be around 40-100 thousand per μl.
Why do you measure
The reticulocyte count is a test used to determine the quantity (absolute and / or percentage) of reticulocytes circulating in the blood. Often, this analysis is associated with hematocrit and hemoglobin measurement.
The reticulocyte count can be used for various purposes:
- Evaluate the functionality of the bone marrow and its ability to respond adequately to the body's red blood cell requirements;
- Support the diagnosis of diseases that affect the production of red blood cells in the blood, such as anemia and bone marrow dysfunctions;
- Diagnose the forms of anemia caused by functional changes in the bone marrow from those resulting from hemorrhage or hemolysis;
- To investigate the causes of altered values related to the number of red blood cells, hemoglobin and hematocrit, after performing a blood count;
- Monitor the effectiveness of the treatment, such as, for example, in the case of iron deficiency anemia, vitamin B12 and folate deficiency, renal failure, chemotherapy or bone marrow transplantation.
In patients with reduced hemoglobin values, reticulocyte counts allow the initial distinction of anemias, especially when normocytic forms are present:
- Without reticulocytosis, caused or associated with reduced production of red blood cells (due to various types of marrow progenitors);
- With reticulocytosis, associated with increased destruction (hemolysis) or loss (hemorrhage), with intact and efficient progenitors, but insufficient to rebalance peripheral damage.
Normal values
Reticulocytes are present both in the bone marrow and in peripheral blood. Normally, reticulocytes represent 0.5-2.5% of circulating erythrocytes and their permanence in the blood stream is 24 hours.
In terms of absolute value, the reference range is 25-75 × 109 / L.
High reticulocytes - Causes
High levels of reticulocytes (reticulocytosis) may be a sign of:
- Pernicious or iron deficiency anemia: the body compensates for this loss or lack of red blood cells, increasing the rate of erythropoiesis; this is reflected in the increased release of reticulocytes in the blood from the bone marrow.
- Kidney diseases.
A high reticulocyte count - associated with hemoglobin, hematocrit and low red blood cells - may indicate the presence of:
- Excessive blood loss: in the presence of acute bleeding or chronic bleeding, the number of reticulocytes increases to compensate for red blood cell deficits.
- Hemolytic anemia: the bone marrow increases the production of red blood cells to compensate for the excessive destruction, with the consequent increase in the number of reticulocytes in the circulation.
- Hemolytic disease in the newborn: in this potentially fatal situation, there is an increased destruction of red blood cells.
If a high number of erythrocytes is associated with a high reticulocyte count, an excessive production of red blood cells could be present, found in some pathologies such as:
- Polycythemia vera;
- Excessive secreting tumors of erythropoietin.
Reticulocytes increase physiologically during pregnancy. Even newborns have high levels of these red blood cell precursors, which normalize within a few days of birth.
An increase in the number of reticulocytes in circulation can also occur when a person goes to higher altitudes than those in which they live. Smokers may also have an increase in the number of reticulocytes.
Low reticulocytes - Causes
Low levels of reticulocytes may be a sign of:
- Lack of various nutrients, including iron, vitamin B12 or folic acid;
- Aplastic anemia;
- Radiotherapy;
- Bone marrow failure caused by infection or cancer;
- Severe renal pathology (with decreased levels of erythropoietin);
- Alcoholism;
- Hepatic cirrhosis;
- Endocrine disorders.
How to measure it
To carry out the examination, the patient must undergo a blood sample from a vein in the arm. The doctor may request that the reticulocyte count be performed on the same sample used for the blood count.
The reticulocyte count is usually achieved by automated methods that measure various parameters present in the blood sample. These instruments allow greater precision, accuracy and reproducibility than microscope analysis, even in the case of very low values (reticulocytopenia).
In the percentage count, the number of reticulocytes is compared with the total value of red blood cells according to the following formula:
Reticulocytes (%) = [number of reticulocytes / number of total red blood cells] x 100
Preparation
It is not necessary to be fasting to have a blood sample useful for reticulocyte counting. The examination takes place, in fact, on the corpuscular part of the blood, that is on the cells, for which the fact of having taken food or drink has no influence. However, when you have to perform some other blood test that includes fasting (such as blood glucose or cholesterol measurement) you will need to refrain from food and drink.
The general practitioner who prescribes the analyzes will still be able to provide the most useful information for the case.
Blood transfusions can influence the result of reticulocyte count.
Interpretation of Results
The reticulocyte count (absolute or percentage) must be interpreted simultaneously with the result of other tests, such as the red blood cell count, hemoglobin, hematocrit and complete blood count.
In general, this parameter reflects bone marrow activity.
The result of reticulocyte evaluation may indicate excessive red blood cell production and provides information about the ability of the bone marrow to meet these needs.
Blood analysis: interpretation of the results
Since the number of reticulocytes is usually expressed as a percentage of the number of circulating erythrocytes, the interpretation of this value must also take into account other factors. For example:
- a normal number of reticulocytes (0.5-2.5%) indicates normal bone marrow activity if the hemoglobin concentration is normal.
- a high reticulocyte count (reticulocytosis), in the presence of normal hemoglobin levels, indicates that red blood cells have been lost or destroyed, but that the marrow has compensated by increasing its production.
- if the concentration of hemoglobin is low and normal reticulocytes, it means that there has been no adequate response to anemia.
Normally, therefore, in an anemic individual, the number of circulating red blood cells will be decreased and the "normal" percentage value of reticulocytes will be increased.
If the function of the bone marrow is normal and the reserves of iron and other necessary substances are adequate, the degree of reticulocytosis is proportional to the degree of blood loss or destruction of red blood cells.
ERITROPOIESI INEFFICACE
Patients with erythrocyte maturation or hemoglobin production defects sometimes have ineffective erythropoiesis (red blood cell maturation). Under these conditions, the erythrocyte population is greatly increased (hyperplastic), but the reticulocyte count is disproportionately low, since many cells never mature enough to enter the circulation. Pernicious anemia and thalassemia are excellent examples of diseases associated with ineffective erythropoiesis.
bleeding and therapeutic response
An increase in the number of reticulocytes that occurs after a blood loss, or in certain anemias such as those due to iron deficiency, after a proper cure has been established, indicates that the bone marrow is responding with an increased production of red blood cells .
A single hemorrhage causes reticulocytosis, which begins within 24-48 hours and reaches a peak after 4-7 days. It returns to normal levels when the hemoglobin concentration normalizes.
The persistence of reticulocytosis indicates a continuous or recurrent blood loss.
In iron deficiency, particularly in anemia caused by chronic blood loss, iron administration induces an increase in reticulocytes within 4-7 days and their count remains high until normal hemoglobin concentrations are reached. Vitamin B12 therapy in pernicious anemia also induces prompt and persistent reticulocytosis.
