Hypochromic red blood cells and reticulocytes.

The management of recombinant human erythropoietin (rHuEPO) treatment in hemodialysis patients requires close monitoring of iron status, because the pharmacologically stimulated erythropoiesis is particularly dependent on a continuous supply of iron. Parameters commonly measured to assess iron status are serum ferritin and the transferrin saturation. Both are indirect measures of iron availability for hemoglobin synthesis and frequently do not permit an assessment of the adequacy of iron supply to the erythron. Using flow cytometry, cell volume and hemoglobin concentration can be measured in individual red blood cells and reticulocytes. Based on these techniques, two parameters have proved to be particularly useful in identifying iron-deficient erythropoiesis. (a) The percentage of hypochromic erythrocytes (defined as red blood cells with a hemoglobin concentration of less than 28 g/dl) has been shown to detect insufficient marrow iron supply with a fairly good accuracy. (b) More recently, determination of the content of hemoglobin in reticulocytes (CHr) has been suggested by a number of authors to be even more sensitive in detecting iron-deficient erythropoiesis. For those who have access to an H*3 hematology analyzer, both indices can be determined at the time of a routine blood count at a minimal incremental cost.