Reticulocyte Index Calculator

How does this reticulocyte index calculator work?

This health tool is designed to compute the reticulocyte production index, RPI based on some blood constant values and can help you assess an appropriate response to anemia, frequently encountered in case of patients suffering of Sickle Cell Disease.

This reticulocyte index calculator has two tabs in order to be helpful both to those trying to find out RPI knowing the hematocrit value and to those who know the hemoglobin value. Below are described each of the tabs and the formulas they work after:

■ RPI method 1

This requires the percentage of reticulocytes from red blood cells also known as the count, the hematocrit value and the normal hematocrit – this is usually accounted as 45%.

There are two steps of the formula, first of all we need to calculate the reticulocyte index and then correct it 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 are explained in the table below:

■ RPI method 2

This method requires the percentage for the reticulocyte count, the tested Hemoglobin and the value considered for Normal Hemoglobin, depending on the age and gender of the patient.

The formula used in this case is RPI = Reticulocyte count x Hemoglobin / Normal Hemoglobin x 0.5

Example of two calculations

■ By 1st approach: Let’s take the example of a person with a reti. count = 3.5% and a Hematocrit value of 30%, the RPI value is = Reticulocyte count x Hematocrit / Normal Hematocrit / Maturation correction = 3.5 x 30 / 45 / 1.5  The result displayed will be:

- Reticulocyte Production Index (RPI) is 1.56.

- Absolute Reticulocyte Index (count) is 2.33.

- Retic survival (days)/ Maturation correction based on Hematocrit(%) is 2.

■ By 2nd method: Let’s consider a person with a reti. count = 3.5% and a hemoglobin value of 12g/dL and taking the normal hemoglobin as 13.5 g/dL. The RPI in this case will be RPI = Reticulocyte count x Hemoglobin / Normal Hemoglobin x 0.5 = (3.5 x 12 / 13.5)  x 0.5 . The result displayed is RPI = 1.56.

RPI and reticulocytes

RPI represents the corrected reticulocyte count and is basically a determination necessary for the accurate report of the number of reticulocytes by taking into account all their development stages. The count from the blood test is in the form of a percent, defining their fraction from the red blood cells, therefore it needs a correction.

This is of value especially in the diagnosis of anemia when the raw count might be misleading because the red blood cells are depleted and the percentage may appear higher than it really is.

RPI assesses whether the bone marrow is functioning properly, given the anemic state as the reticulocyte production should increase as response to the red blood cells loss.

If the response is not appropriate, either the anemia is due to an acute cause or the bone marrow is not adapting to it properly, in this case talking about a bone marrow defect such as insufficient erythropoietin.

RPI interpretation

■ The normal range of the reticulocyte count is 0.5 to 2.5% and when this applies to a healthy hematocrit of 45% then the correction factor being one, the RPI is also between 0.5 and 2.5%.

■ RPI lower than 2 accompanied by anemia is a signal of RBC loss and decreased production of reticulocytes.

■ RPI greater than 3 accompanied by anemia suggests RBC loss but an increased production or reticulocytes.

Reference

Poorana PP, Subhashree AR. (2014) Role of Absolute Reticulocyte Count in Evaluation of Pancytopenia-A Hospital Based Study - J Clin Diagn Res; 8(8): FC01–FC03.