Reticulocyte production index

This calculation is necessary because the raw reticulocyte count is misleading in anemic patients.

In anemia, the patient's red blood cells are depleted, creating an erroneously elevated reticulocyte count.

They are slightly larger than totally mature red blood cells, and have some residual ribosomal RNA.

The presence of RNA allows a visible blue stain to bind or, in the case of fluorescent dye, result in a different brightness.

[2] The RPI is used to assess whether the bone marrow is producing an appropriate response to an anemic state.

Reticulocyte production should increase in response to any loss of red blood cells.

[3] If reticulocyte production is not raised in response to anemia, then the anemia may be due to an acute cause with insufficient time to compensate, or there is a defect with red blood cell production in the bone marrow.

Marrow defects include nutritional deficiencies (i.e. iron, folate, or B12) or insufficient erythropoietin, the stimulus for red blood cell production.

Reticulocytopenia, or "aplastic crisis", is the medical term for an abnormal decrease of reticulocytes in the body The reticulocyte production index may find new use as a more reliable detector of erythropoietin-doping in athletes.

[4] 2.The next step is to correct for the longer life span of prematurely released reticulocytes in the blood—a phenomenon of increased red blood cell production.

This relies on a table: So, in a person whose reticulocyte percentage is 5%, hemoglobin 7.5 g/dL, hematocrit 25%, the RPI would be:

The simplest method for correcting the reticulocyte count, to obtain a more accurate daily production index, is to divide the corrected count by a factor of 2 (or multiply with ½) whenever polychromasia (the presence of immature marrow reticulocytes or "shift" cells) is observed on the smear or the immature fraction on the automated counter is increased.