Reticulocytes are immature
red blood cellRed blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s, typically composing about 1% of the red cells in the human body.
Reticulocytes develop and mature in the red
bone marrowBone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
and then circulate for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells, reticulocytes do not have a
cell nucleusIn cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
. They are called reticulocytes because of a reticular (mesh-like) network of
ribosomalA ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
RNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
that becomes visible under a microscope with certain stains such as
new methylene blueNew methylene blue is an organic staining agent used in diagnostic cytopathology and histopathology, typically for staining immature red blood cells. It is closely related to methylene blue, an older stain already in wide use....
.
Process
To accurately measure reticulocyte counts, automated
countersFlow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
that use lasers mark cell samples with fluorescent dye that marks
RNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
(such as thiazole orange or
polymethinePolymethines are compounds made up from an odd number of methine groups bound together by alternating single and double bonds.Compounds made up from an even number of methine groups are known as polyenes....
). This distinguishes reticulocytes as the middle ground of dye response to laser light, between red blood cells (which have neither RNA nor DNA) and
lymphocyteA lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s (which have a large amount of DNA, unlike reticulocytes).
The specimen requirement for a reticulocyte count is
EDTAEthylenediaminetetraacetic acid, widely abbreviated as EDTA , is a polyamino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylenediaminetetraacetate. It is widely used to dissolve limescale. Its usefulness arises because of its role as a hexadentate ligand...
anti-coagulated whole blood (lavender-top bottle if using the
VacutainerVacutainer is a brand of test tubes specifically designed for venipuncture, which was developed in 1947 by Joseph Kleiner.In phlebotomy the word “vacutainer” has come to be used as a genericized trademark to describe any vacuum-based blood collection vial, regardless of brand. Becton Dickinson...
, Vacuette or Monoject systems; red-top if using the S-Monovette system).
Reticulocytes appear slightly bluer than other red cells when looked at with the normal Romanowsky stain. Reticulocytes are also slightly larger, which can be picked up as a high MCV (mean corpuscular volume) with a full blood count done by a trained medical scientist, who has specialized in hematology, or a machine.
Flowcytometry for mouse reticulocytes: One can use a cell-permeable thiazole orange dye (see above) to stain for reticulocytes' residual RNA in conjunction with DRAQ5 DNA-only dye (reticulocytes have no DNA and are, thus, DRAQ5-negative) and Ter119 (glycophorin-A) that is a marker of erythroid lineage. (Thiazole orange dye binds to nucleic acids of both DNA and RNA).
Interpretation
The normal range of values for reticulocytes in the blood depends on the clinical situation and the lab, but, in general terms, is 0.5% to 1.5%. However, if a person has
anemiaAnemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, his/her reticulocyte percentage should be higher than "normal" if the bone marrow's ability to produce new blood cells remains intact. Thus, calculating the reticulocyte production index is an important step in understanding whether the reticulocyte count is appropriate or inappropriate to the situation. This is often a more important question than whether the percentage is in the normal range; for instance, if someone is anaemic but has a reticulocyte percentage of only 1%, the bone marrow is likely not producing new blood cells at a rate that will correct the anaemia. The number of reticulocytes is a good indicator of
bone marrowBone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
activity, because it represents recent production. This means that the reticulocyte count, and the reticulocyte production index that can be calculated from it, can be used to determine whether a production problem is contributing to the anaemia, and can also be used to monitor the progress of treatment for anaemia.
When there is an increased production of red blood cells to overcome chronic or severe loss of mature red blood cells, such as in a haemolytic anaemia, people often have a markedly high number and percentage of reticulocytes. A very high number of reticulocytes in the blood can be described as
reticulocytosisReticulocytosis is a condition where there is an increase in reticulocytes, immature red blood cell.It is commonly seen in Anemia. They are seen on blood films when the bone marrow is highly active in an attempt to replace red blood cell loss such as in haemolytic anaemia, haemorrhage.-External...
.
Abnormally low numbers of reticulocytes can be attributed to
chemotherapyChemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
, aplastic anaemia, pernicious anaemia,
bone marrowBone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
malignancies, problems of
erythropoietinErythropoietin, or its alternatives erythropoetin or erthropoyetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production...
production, various vitamin or mineral deficiencies (B
9, B
12, iron), disease states (
anaemia of chronic diseaseAnemia of chronic disease, also referred to as anemia of inflammatory response is a form of anemia seen in chronic illness, e.g. from chronic infection, chronic immune activation, or malignancy...
) and other causes of anaemia due to poor RBC production.
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