In the text below the calculator there is more information on the two determination methods and an RPI interpretation.
The reticulocyte index uses the percentage of immature red blood cells and either haemoglobin or haematocrit to determine the reticulocyte production index. This can offer complete information about the composition of RBCs in terms of cells at all stages of maturation.
RPI is used in assessing the response to anemia, especially in patients diagnosed with Sickle Cell disease.
The two formulas used to determine the reticulocyte production index are:
■ RPI (via hematocrit) = Reticulocyte count x Hematocrit / Normal Hematocrit / Maturation correction
■ RPI (via hemoglobin) = Reticulocyte count x Hemoglobin / Normal Hemoglobin x 0.5
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Reticulocyte production index explained
The RPI is the corrected reticulocyte count which accounts for all reticulocytes in all development stages. This is particularly useful in conditions such as anemia where there are RBCs in circulation at different stages of maturation.
The reticulocyte count provided in a normal complete blood count test is provided as a percent, defining their fraction in the red blood cells but does not account for different stages.
By associating reticulocytes with hematocrit or hemoglobin determinations, an accurate view in the bone marrow response can be obtained.
There are two different methods, that can be found in the two tabs of the calculator.
RPI method 1
The first method uses the following variables:
■ Percentage of reticulocytes (from RBCs);
■ Hematocrit (as measured);
■ Normal haematocrit (most commonly accounted as 45%).
There are two steps in this method: firstly, the reticulocyte index is calculated then it needs to be adjusted by a maturation correction to reflect the longer life span of premature reticulocytes.
Reticulocyte Index = Reticulocyte count x Hematocrit / Normal Hematocrit
RPI = Reticulocyte index/ Maturation correction
The correction rates used can be found in the table below:
|Hematocrit (%)||Maturation correction|
|16 - 25||2|
|26 - 35||1.5|
|36 - 45||1|
RPI method 2
Uses the following variables:
■ Percentage of reticulocytes;
■ Hemoglobin (as measured);
■ Normal haemoglobin (depending on patient age and gender).
RPI = Reticulocyte count x Hemoglobin / Normal Hemoglobin x 0.5
The reticulocyte production index is most often used in the diagnosis of anemias. This is because in these conditions the raw RBC count may be misleading (appear higher than it actually is) because the cells are depleted.
In anemia, the reticulocyte production should increase as response to the red blood cells loss and the RPI verifies if the bone marrow response is appropriate.
In cases RPI does not adapt, there are two main causes:
■ The anemia is due to an acute cause;
■ There is a bone marrow defect such as insufficient erythropoietin.
Normal RPI varies between 0.5 and 2.5%. However, in case anemia is present and RPIs are lower than 2%, this is still consistent with RBC loss and decreased production of reticulocytes.
Values lower than 0.5 indicate a very decreased reticulocyte production.
Values greater than 3, when accompanied by anemia, indicate RBC loss but an increased production of reticulocytes.
Poorana P, Subhashree AR. Role of Absolute Reticulocyte Count in Evaluation of Pancytopenia-A Hospital Based Study. J Clin Diagn Res. 2014; 8(8): FC01–FC03.
No. Of Variables: 3
Year Of Study: 2014
Published On: June 7, 2017 · 07:31 AM
Last Checked: June 7, 2017
Next Review: June 7, 2023