THE reticulocytes they are the transition elements between nucleated erythroblasts (proerythroblasts) and red blood cells. These cells of the erythroid lineage are produced in the bone marrow and, when released into the bloodstream, take on the characteristics of the erythrocyte, after maturation of approximately one day (note: the entire differentiation process lasts 10 days).
Reticulocytes are defined by the presence of cytoplasmic material, consisting mainly of mitochondria and residues of genetic material (ribosomal ribonucleic acid), visible as granules and filaments on supravital staining, such as cresyl brilliant blue.
Red blood cells survive in circulation for about 120 days; consequently, the bone marrow is continuously engaged in the production of new erythrocytes, which replace the old or degraded ones. In this way, a constant number of red blood cells is always maintained in the blood.
There absolute or percentage reticulocyte count it is a good indicator of the ability of a person’s bone marrow to produce red blood cells (erythropoiesis).
Reticulocytes: biological role and normal values
In adults, approximately 2 million red blood cells are produced per second. During the maturation of the cell, 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 a mature erythrocyte (which will have a lifespan of approximately 120 days). Thus, reticulocytes are the young, still immature red blood cells, and are 0.5% – 2.5% of circulating red blood cells. For example, in a subject who has 5 million red blood cells per μl, the reticulocytes will be approximately 40-100 thousand per μl.
Reticulocytes are present both in the bone marrow and in the peripheral blood. Normally, reticulocytes represent 0.5-2.5% of circulating erythrocytes and their presence in the bloodstream is 24 hours.
In terms of absolute value, the reference range is 25-75 ×109/L.
High Reticulocytes – Causes
High levels of reticulocytes (reticulocytosis) can be a sign of:
- Pernicious or iron deficiency anemia: the body compensates for this loss or deficiency of red blood cells by increasing the rate of erythropoiesis; this is reflected in the increased release of reticulocytes into the blood by the bone marrow.
- Kidney diseases.
A high reticulocyte count – associated with low hemoglobin, hematocrit and red blood cells – may indicate the presence of:
- Excessive blood loss: In the presence of an acute hemorrhage 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 their excessive destruction, with the consequent increase in the number of reticulocytes in circulation.
- Hemolytic disease in the newborn: in this potentially fatal situation, there is increased destruction of red blood cells.
If a high number of erythrocytes is associated with a high reticulocyte count, there may be excessive production of red blood cells, which can be found in some pathologies such as:
Reticulocytes increase physiologically during pregnancy. Newborns also have high levels of these red blood cell precursors, which normalize within a few days of birth.
An increase in the number of circulating reticulocytes can also occur when a person travels to higher altitudes than where they live. Smokers can also have an increase in the number of reticulocytes.
To undergo the blood test useful for the reticulocyte count it is not necessary to be fasting. In fact, the test takes place on the corpuscular part of the blood, i.e. on the cells, for which the fact of having consumed food or drink has no influence. However, when you have some other blood test that involves fasting (such as measuring blood sugar or cholesterol) you will need to abstain from food and drink.
The GP who prescribes the tests will still be able to provide the most useful information in the case.
Blood transfusions can affect the result of the reticulocyte count.
Interpretation of Results
The reticulocyte count (absolute or percentage) should be interpreted in conjunction with the results of other tests, such as red blood cell count, hemoglobin, hematocrit, and complete blood count.
Generally speaking, this parameter reflects the activity of the bone marrow.
The result of the reticulocyte evaluation may indicate excessive production of red blood cells and provides information about the ability of the bone marrow to respond to these needs.
Blood tests: interpretation of results
Since, usually, the number of reticulocytes is expressed as a percentage value compared to the number of circulating erythrocytes, the interpretation of this value must also take into account other factors. For example:
- a normal number of reticulocytes (equal to 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 their production.
- if the hemoglobin concentration is low and the reticulocytes are normal, it means that there has been no adequate response to the 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 bone marrow function is normal and 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.
Patients with defects in erythrocyte maturation or hemoglobin production 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, because many cells never mature enough to enter the circulation. Pernicious anemia and thalassemia are excellent examples of diseases associated with ineffective erythropoiesis.
hemorrhages and therapeutic response
An increase in the number of reticulocytes that occurs after blood loss, or in certain anemias such as iron deficiency, after adequate treatment has been established, indicates that the bone marrow is responding with increased production of red blood cells .
A single hemorrhage causes reticulocytosis, which begins within 24 to 48 hours and reaches a peak after 4 to 7 days. Normal levels return when the hemoglobin concentration normalizes.
Persistent reticulocytosis indicates 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 elevated until normal hemoglobin concentrations are reached. Vitamin B12 therapy in pernicious anemia also induces prompt and persistent reticulocytosis.