reticulocyte production index

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Reticulocytes are newly produced red blood cells. 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. This allows them to be detected and counted as a distinct population.Adamson JW, Longo DL. Anemia and polycythemia. in: Braunwald E, et al. Harrison's Principles of Internal Medicine. (15th Edition). McGraw Hill (New York), 2001.

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. It should increase within 2–3 days of a major acute hemorrhage, for instance, and reach its peak in 6–10 days.Hoffbrand AV, et al. Essential Haematology. (Fourth Edition) Blackwell Science (Oxford), 2001. 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. The use of this method is referred to as "biological passport."{{citation needed|date=July 2020}}

Reticulocyte Production Index is calculated as follows:

1.$Corrected\; Retic\; Percentage\; =\; Retic\; Percentage\; *\; \{Hematocrit\; \backslash over\; Normal\; Hematocrit\}$

This calculation is to correct for the severity of the anemia.

A value of 45% (or 0,45 L/L) is usually used as a normal hematocrit for males.{{cite web |url=http://peir.path.uab.edu/heme/messages/637/648.html |title=UAB Hematopathology |accessdate=2009-02-07 |url-status=dead |archiveurl=https://web.archive.org/web/20090916013600/http://peir.path.uab.edu/heme/messages/637/648.html |archivedate=2009-09-16 }}

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:

$RPI\; =\; \{Corrected\; Retic\; Percentage\; \backslash over\; Maturation\; Correction\}$ → RPI $=\; \{\{5\; *\; \{25\; \backslash over\; 45\}\}\; \backslash over\; 2\}\; =$1.4

Alternatively some books provide the following formula and is called Reticulocyte Index (RI):

Whereas normal reticulocytes lose their RNA within 24 hours, a severely anemic patient with a full erythropoietin response will release reticulocytes that take from 2-3 days to lose their RNA. This has the effect of raising the reticulocyte count simply because reticulocytes produced on any single

day will spend more than 1 day in circulation as reticulocytes and, therefore, will be counted for 2 or more days. 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.{{Cite web|url=https://hemonc.mhmedical.com/content.aspx?bookid=1802§ionid=124977820|title=HEMOLYTIC ANEMIAS | Hematology in Clinical Practice, 5e | AccessHemOnc | McGraw Hill Medical|website=hemonc.mhmedical.com}}R. S. Hillman, et al. Hematology in Clinical Practice. (Fifth Edition) McGraw-Hill (LANGE), 2010.{{Cite web|url=https://www.scribd.com/doc/313501203/Practical-Pediatric-Hematology|title = Practical Pediatric Hematology | Anemia | Red Blood Cell}}

$RI\; =\; Retic\; Percentage\; *\; \{Hematocrit\; \backslash over\; Normal\; Hematocrit\}*0.5$ → $RI\; =\; 5\; *\; \{25\; \backslash over\; 45\}*0.5\; =$1.4

• The reticulocyte index (RI) should be between 0.5% and 2.5% for a healthy individual.Hoffbrand, A.V, Moss, P.A.H, (2011), Essential Haemotology,6th Ed, Wiley and Blackwell; West Sussex, UK.
• RI < 0.5% with anemia indicates maturation disorder, meaning loss of red blood cells, but also decreased production of reticulocytes (i.e., an inadequate response to correct the anemia) and therefore red blood cells.
• RI > 2.5% with anemia indicates loss of red blood cells (from causes such as destruction, bleeding, etc.), with an increased compensatory production of reticulocytes to replace the lost red blood cells.

Interpretation of these values are not standard and vary based on specific laboratory values and clinical context.{{Cite web|url=http://www.sysmex.ru/files/articles/Xtra_online_reticulocytes.pdf|title = Sysmex Europe GMBH - Lighting the way with diagnostics}}

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Category:Blood tests