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A reticulocyte count is a blood test performed to assess the body's production of immature red blood cells (reticulocytes). A reticulocyte count is usually performed when patients are evaluated for anemia and response to its treatment. It is sometimes called a retic count.
A reticulocyte count provides information about the rate at which the bone marrow is producing red cells. A normal count means that the production is adequate; a decreased count means it is not. This information helps determine whether a lack of red cells in an anemic person is caused by a bone marrow problem, by excessive bleeding, or by red cell destruction.
The test is also used to monitor the response of bone marrow response to treatment for anemia. The reticulocyte count rises within days if the treatment is successful. It is also used following bone marrow transplant to evaluate the new marrow's cell production.
Reticulocytes were first described as transitional forms of red blood cells by Wilhelm H. Erb in 1865. A red cell begins in the bone marrow as a large bluish cell filled with ribonucleic acid (RNA). As the cell matures, it shrinks. Its color gradually changes from blue to pink as its load of oxygen-carrying protein (hemoglobin) increases and the RNA decreases. The center of the cell (nucleus) becomes clumped. It is expelled three days before the cell leaves the bone marrow. The cell is now a reticulocyte. On its fourth and final day of maturation, the reticulocyte enters the bloodstream. One day later, it is a mature red blood cell.
The first step in a retic count is drawing the patient's blood sample. About 17 oz (5 ml) of blood is withdrawn from a vein into a vacuum tube. The procedure, which is called a venipuncture, takes about five minutes.
After the sample is collected, the blood is mixed with a dye (methylene blue) in a test tube. The RNA remaining in the reticulocytes picks up a deep blue stain. Drops of the mixture are smeared on slides and examined under a microscope. Reticulocytes appear as cells containing dark blue granules or a blue network. The laboratory technologist counts 1,000 red cells, keeping track of the number of reticulocytes. The number of reticulocytes is reported as a percentage of the total red cells. When the red cell count is low, the percentage of reticulocytes is inaccurately high, suggesting that more reticulocytes are present than there are in reality. The percentage is mathematically corrected for greater accuracy. This figure is called the corrected reticulocyte count or reticulocyte index.
Reticulocyte counts can also be done on automated instruments, such as flow cytometers, using fluorescent stains. These instruments are able to detect small changes in the reticulocyte count because they count a larger number of cells (10,000-50,000).
The doctor should make a note of any prescription medications that the patient is taking. Some drugs lower the red blood cell count.
Aftercare consists of routine care of the area around the puncture mark. Pressure is applied for a few seconds and the wound is covered with a bandage.
The primary risk is mild dizziness and the possibility of a bruise or swelling in the area where the blood was drawn. The patient can apply moist warm compresses.
Adults have reticulocyte counts of 0.5-2.5%. Women and children usually have higher reticulocyte counts than men.
A low reticulocyte count indicates that the bone marrow is not producing a normal number of red blood cells. Low production may be caused by a lack of vitamin B12, folic acid, or iron in the diet; or by an illness affecting the bone marrow (for example, cancer). Further tests are needed to diagnose the specific cause.
The reticulocyte count rises when the bone marrow makes more red cells in response to blood loss or treatment of anemia.
Rowan, R. M., et al. "The Reticulocyte Count: Progress Towards the Resurrection of a Useful Clinical Test." Clinical and Laboratory Haematology 18, no. 1 (1996): 3-8.
Anemia — A condition marked by a decrease in the number or size of red blood cells
Methylene blue — A dye that is used to stain the blood cells for the reticulocyte count.
Reticulocyte — An immature red blood cell.
a numerical computation or indication.
Addis count the determination of the number of erythrocytes, leukocytes, epithelial cells, and casts, and the protein content in an aliquot of a 12-hour urine specimen; used in the diagnosis and management of kidney disease.
blood count (blood cell count) see blood count.
blood count, complete a series of tests of the peripheral blood, including the erythrocyte count, erythrocyte indices, leukocyte counts, and sometimes platelet count.
blood count, differential differential leukocyte count.
erythrocyte count determination of the number of erythrocytes in a unit volume of blood that has been diluted in an isotonic solution, done with an automatic counter such as a flow cytometer. Called also red blood cell or red cell count.
leukocyte count determination of the number of leukocytes in a unit volume of blood, usually after the erythrocytes have been lysed and the blood has been diluted; it may be done either manually with a hemacytometer or electronically. See total leukocyte c. and differential leukocyte c. Called also white blood cell or white cell count.
leukocyte count, differential a leukocyte count that calculates the percentages of different types. See also total leukocyte count.
leukocyte count, total a leukocyte count measuring the total number of all the types in a given volume of blood. See also differential leukocyte count.
platelet count determination of the total number of platelets per cubic millimeter of blood; the direct platelet count simply counts the cells using a microscope, and the indirect platelet count determines the ratio of platelets to erythrocytes on a peripheral blood smear and computes the number of platelets from the erythrocyte count.
red blood cell count (red cell count) erythrocyte count.
reticulocyte count a calculation of the number of reticulocytes in 1 cu mm of peripheral blood, recorded either as an absolute number or as the percentage of the erythrocyte count. It provides a means of assessing the erythropoietic activity of the bone marrow.
white blood cell count (white cell count) leukocyte count.
a count of the number of reticulocytes in a whole blood specimen, used in determining bone marrow activity. The reticulocyte count is lowered in hemolytic diseases and chronic infection; it is elevated after hemorrhage or during recovery from anemia. The normal concentration of reticulocytes in whole blood in adults is 0.5% to 1.5% of total red blood cells.
reticulocyte countThe number of immature erythrocytes–reticulocytes in peripheral blood that have a basophilic reticulum–residual RNA when stained with supravital dyes–eg, methylene blue, brilliant cresyl blue; the RC is used to evaluate the rate of RBC production, and BM response to anemia ↓ in ↓ adrenocortical and anterior pituitary activity, aplastic anemia, cirrhosis, megaloblastic anemia, exposure to radiation↑ in Erythroblastosis fetalis, HbC, leukemia, after hemorrhage, pregnancy, thalassemia, during treatment of iron and megaloblastic anemia Normal range Newborn < 6.5% of peripheral RBCs; children < 2%; adults < 1%
a stage of erythrocyte maturation, between normoblast (metarubricyte) and mature erythrocyte, showing a basophilic reticulum (residual RNA) under vital staining.
corrected reticulocyte percentage (CRP)
percentage reticulocytes ÷ (hematocrit ÷ normal hematocrit); a measure of reticulocyte numbers adjusted for the degree of anemia.
performed on blood mixed with a supravital stain such as new methylene blue or brilliant cresyl blue. An increased count indicates active erythropoiesis.
reticulocyte production index (RPI)
corrects the reticulocyte count, taking into account the presence of anemia and the presence of shift reticulocytes producing a more accurate indicator of red cell production.
the release of reticulocytes in response to erythropoietin or administration of specific therapy for anemia, e.g. a deficiency of iron or folic acid. A reticulocyte response does not develop until the anemia is marked in cattle and not at all in horses.
shift reticulocyte, stimulated reticulocyte
with intense stimulation of erythropoiesis there is premature release of reticulocytes from the bone marrow into peripheral blood. These are larger and contain more reticulum than normal reticulocytes.