Reticulocyte index 2848180 215231186 2008-05-27T08:38:04Z Bongwarrior 1879566 Reverted edits by [[Special:Contributions/Paraside|Paraside]] ([[User talk:Paraside|talk]]) to last version by 129.98.123.65 {{Orphan|date=November 2006}} The '''Reticulocyte production index''' (RPI, also called a ''corrected reticulocyte count'') is a calculated value used in the diagnosis of [[anemia]]. This calculation is necessary because the raw [[reticulocyte count]] is misleading in anemic patients. The problem arises because the reticulocyte count is not really a ''count'' but rather a ''percentage'': it reports the number of reticulocytes as a percentage of the number of red blood cells. In anemia, the patient's red blood cells are depleted, creating an erroneously elevated reticulocyte count. [[Reticulocyte]]s 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.{{ref|Adamson}} The idea of the RPI is 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.{{ref|Hoffbrand}} 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. Reticulocyte Production Index is calculated as follows: '''1.'''<math>Retic Index = Retic Count * {Hematocrit \over Normal Hematocrit}</math> A value of 45 is usually used as a normal hematocrit. '''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: '''Hematocrit (%)......Retic survival (days)/maturation correction''' * 36-45........................1.0 * 26-35........................1.5 * 16-25........................2.0 * 15 and below.............2.5 '''So,''' in a person whose reticulocyte count is 5%, hemoglobin 7.5 g/dL, hematocrit 25%, the RPI would be: ''[retic index]/[maturation correction] = [5 x (25/45)] /2'' = '''1.4''' *The reticulocyte index (RI) should be between 1.0 and 2.0 for a healthy individual. *RI < 2 with anemia indicates decreased production of reticulocytes and therefore red blood cells.{{ref|Adamson}} *RI > 2 with anemia indicates loss of red blood cells (destruction, bleeding, etc) leading to increased compensatory production of reticulocytes to replace the lost red blood cells.{{ref|Adamson}} ==References== * {{note|Adamson}} 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. * {{note|Hoffbrand}} Hoffbrand AV, et al. ''Essential Haematology.'' (Fourth Edition) Blackwell Science (Oxford), 2001. ==External links== *[http://medcalc3000.com/ReticProdIndex.htm Medical Calculator] Online RPI calculator, "for educational purposes only". [[Category:Blood]] [[Category:Hematology]] {{Blood}}