Table of ContentsView AllTable of ContentsWhat Does the Test Measure?Purpose of TestBefore the TestDuring the TestAfter the TestInterpreting ResultsTreatment for High ReticulocytesTreatment for Low ReticulocytesSummary
Table of ContentsView All
View All
Table of Contents
What Does the Test Measure?
Purpose of Test
Before the Test
During the Test
After the Test
Interpreting Results
Treatment for High Reticulocytes
Treatment for Low Reticulocytes
Summary
Reticulocytes are “adolescent” red blood cells that have just been released from the bone marrow into the circulation and are present in the blood for only around one day before maturing into “adult” red blood cells. The reticulocyte count is a test to measure the level of reticulocytes in your blood. It is extremely valuable in determining the health of the bone marrow and can play a key role in the initial workup of anemia.
This article will go over what a reticulocyte count measures, when this test is performed, and what the different values mean.
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An Overview of Anemia
The bone marrow is continually replenishing red blood cells so that roughly 1% of the red blood cells are reticulocytes at any time. A high reticulocyte count may be seen with bleeding or breakdown of red blood cells, as the bone marrow releases more reticulocytes to compensate for the loss. In contrast, a low reticulocyte count can mean that the bone marrow isn’t functioning properly or that a deficiency (such as iron) is interfering with the production of red blood cells.
Higher Than Normal Reticulocyte Count
A high reticulocyte count may be seen with bleeding or breakdown of red blood cells, as the bone marrow releases more reticulocytes to compensate for the loss.
Lower Than Normal Reticulocyte Count
In contrast, a low reticulocyte count can mean that the bone marrow isn’t functioning properly or that a deficiency (such as iron) is interfering with the production of red blood cells.
The reticulocyte count (known as absolute reticulocyte count) can be misleading when anemia is present, and one or two calculations (the corrected reticulocyte count and reticulocyte production index) may be needed to make sure the count accurately describes what is happening in the bone marrow.
Reticulocytes are immature (but without a nucleus) red blood cells that are named for their granular or “reticulated” appearance under the microscope. There are a number of reasons why a healthcare provider may order a reticulocyte count. Some of these include the following:
Reticulocyte Count Measurement and Meaning
Red blood cells normally live in the bloodstream for around 120 days but are continuously being replenished from the bone marrow.
The reticulocyte count is a measure of the immature red blood cells (reticulocytes or “adolescent” red blood cells) recently released from the bone marrow into the circulation and is ordinarily around 1% in people who have a normal red blood cell count.
Absolute Reticulocyte Count
Reticulocyte Count (Percent) = Number of Reticulocytes / Number of Red Blood Cells
While a normal reticulocyte count in someone who is not anemic is around one, the reticulocyte count is expected to increase with anemia to different degrees. It’s thought that the bone marrow is capable of producing up to eight times as many red cells when necessary.
If the reticulocyte does not increase, it suggests that there is a problem in the bone marrow or a deficiency of substances needed to make red blood cells.
Corrected Reticulocyte Count and Reticulocyte Production Index
If a person has anemia, the absolute reticulocyte count can be misleading, as it can be difficult to know whether or not the reticulocyte count has increased to the degree expected with the severity of a case of anemia. Calculations to determine the corrected reticulocyte count and sometimes the reticulocyte production index can solve this problem.
Testing
The reticulocyte is usually tested using an automated analyzer, but the test may be done manually as well or when results obtained are in question.
Limitations
There are a few limitations with the reticulocyte count that could lead to less accurate or inaccurate results. If a person has had a recentblood transfusion, the count will reflect both the person’s bloodand the donated blood.
Lab errors, such as inaccurate counting (when done manually), procedural problems in drawing the blood, inadequate refrigeration of the sample, or contamination sometimes occur.
False positives (a falsely high reticulocyte count) can occur when cells with other red blood cell inclusions are mistakenly thought to be reticulocytes. Examples include Howell-Jolly bodies, Heinz bodies, siderocytes, and more.
Complementary Tests
A reticulocyte count is usually ordered along with (or after) a complete blood count (CBC). Thecomplete blood count(CBC) includes the total number of the different types of blood cells present.
Thered blood cell indicesincluded in the CBC describe characteristics of the red blood cells and are very helpful in the diagnosis of anemia when combined with the reticulocyte count.
In addition to these tests, other tests may be ordered to evaluate anemia, including a peripheral blood smear for morphology, iron studies, and more.
Risks and Contraindications
There are few risks related to checking a reticulocyte count other than mild discomfort, and rarely bleeding or infection related to the blood draw.
Blood for a reticulocyte count may be drawn in a hospital as well as many clinics.
There is no dietary or activity restriction before having a reticulocyte count done. You should bring your insurance card to your appointment and any medical records (such as previous CBCs or reticulocyte counts) you have at another clinic for comparison.
The actual blood test usually takes only a few minutes. The steps include:
Infants and Young Children
The technique used to collect blood samples from children will depend on their age and/or weight. For newborns and infants up to about 6 months, a heel prick may be used. For all other children, blood is drawn from a vein in the arm.
Regardless of the method used, there are ways you can help your child cope with getting blood drawn:
If you have your blood drawn in a lab, you will be able to leave right after the test and return to your clinic or home to be notified of the results. Side effects are uncommon, but may include bruising at the site of the draw (a hematoma), persistent bleeding, and rarely, infection.
When your healthcare provider receives your results, they will either discuss them with you in the clinic or hospital or call you.
Reference Range
The reference range for the reticulocyte count depends on whether the hematocrit is normal or low. When anemia is not present, the absolute reticulocyte may be used. With anemia, the reticulocyte count is corrected for the low hematocrit, and if very low, is corrected for changes that occur in relation to severe anemia.
Absolute Reticulocyte CountThe normal range for the reticulocyte count without anemia is:Adults: .5% to 1.5%Newborns: 3% to 6%
The normal range for the reticulocyte count without anemia is:Adults: .5% to 1.5%Newborns: 3% to 6%
The normal range for the reticulocyte count without anemia is:
With anemia, it would be expected that the reticulocyte count would be high, as the response to anemia is for the bone marrow to increase production. In this situation, a low or even normal reticulocyte count may be a sign that the bone marrow isn’t functioning as it should. Unfortunately, when anemia is present, the absolute reticulocyte count may not reflect what is really happening in the bone marrow. To compensate for this lack of clarity, a first correction is made.
Corrected Reticulocyte Count (CRC): First Correction
The reference range for corrected reticulocyte count in adults is 0.5 to 1.5%
For severe anemia (hemoglobin less than 12 or hematocrit less than 36), a second correction is needed.
Reticulocyte Production Index (RPI): Second Correction
The problem with using the corrected reticulocyte count alone is that in severe anemia, reticulocytes live roughly two days in the bloodstream rather than one. Using the corrected reticulocyte count, the count could be falsely high for this reason.
Reticulocyte Production Index = Corrected Reticulocyte Count /Maturation Correction
Maturation Correction
The maturation correction depends on the level of anemia:
Of note is that with mild anemia (hemoglobin of 12 or more or a hematocrit of 36 or higher), the maturation correction is 1 so the corrected reticulocyte count will be the same as the RPI.
Using CRC or RPI to Determine the Category of Anemia
Once the corrected reticulocyte count is calculated (and the RPI when indicated), it’s possible to separate out the two broad categories of anemia—whether the bone marrow is functioning normally and trying to compensate for the anemia (compensated anemia), or if the bone marrow is sluggish for some reason (uncompensated anemia).
The reticulocyte count helps distinguish one of the two broad categories of anemia:
Causes of a High Reticulocyte Count (or CRC and RPI With Anemia)
In people with anemia, an elevated reticulocyte count is actually a positive finding in some ways, as it means that the bone marrow is doing its job. A high reticulocyte count is sometimes referred to as “reticulocytosis.”
With anemia, a high reticulocyte count is seen in a few situations:
In people without anemia, an elevated reticulocyte count may be seen with:
Causes of a Low Reticulocyte Count (or CRC and RPI With Anemia)
A low reticulocyte count means that the bone marrow isn’t producing red blood cells as well as it should. In people without anemia, a low reticulocyte count may be seen with some medications.
With anemia, possible causes of a low reticulocyte may include:
Other conditions that may result in a low reticulocyte count include kidney disease (lack oferythropoietin), liver disease, and radiation exposure.
Next Steps
After looking at the reticulocyte count along with other blood test results, a cause may be established, or further workup may be needed to further narrow done the possible diagnoses.
Further Workup
Often further tests will be needed.
If the reticulocyte count is low, possible tests may include:
If the reticulocyte count is high, potential tests may include:
Other labs, imaging tests, or procedures may be recommended as well.
When a reticulocyte count will be repeated will depend on many factors. There are some situations in which a follow-up test is frequently done. After treatment has been initiated for iron, folate, or vitamin B12 deficiency, and once the nutrients have been supplied for manufacturing hemoglobin or red blood cells, the reticulocyte count should increase. If it does not, further evaluation to determine the reason why (or if it may be that more than one type of anemia is present) will likely be recommended.
As a follow-up after a bone marrow transplant or chemotherapy, a reticulocyte count may be done to see how well the bone marrow is responding after these treatments.
Treatment for a high reticulocyte count involves treating the underlying cause. This may include:
Treatment for a low reticulocyte count involves treating the underlying cause. This may include:
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