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Reticulocyte Production Index (RPI)

Purpose: To calculate the reticulocyte production index (RPI) using the reticulocyte maturation time (RMT).

Description

In anemia reticulocytes are prematurely released into the peripheral circulation. It takes time before they mature into normal RBCs. When corrections are done for both the hematocrit and maturation time, the final count is called the "Reticulocyte Production Index" or RPI.


 

The correction for maturation time is called the "shift correction." This consists of dividing the reticulocyte count by a factor determined by the patient's hematocrit. This factor is the number of days it takes a reticulocyte to mature once released into the peripheral blood and is listed in second column below.

 

No correction is needed if the hematocrit is greater than 45% (RMT = 1).

Hematocrit

RMT in Days

40-45%

1.0

35-39%

1.5

25-34%

2.0

15-24%

2.5

05-14%

3

 

where:

• RMT = reticulocyte maturation time

 

RPI =

= (reticulocyte index) / (maturation time in days, from table)

= (observed reticulocyte count, as a percent) * (patient's hematocrit) / 45 / 1% / (maturation time in days, from table)

 

Interpretation:

• minimum RPI: 0

• maximum RPI: > 5

 

RPI

Interpretation in an anemic patient

< 2

bone marrow erythroid hypoproduction of red blood cells (inadequate proliferative response or ineffective erythropoiesis)

2 – 3

borderline response

> 3

bone marrow erythroid hyperproduction, such as occurs in response to anemia.

 


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Specialty

Objective

ICD-10