Reticulocyte Hemoglobin
Reticulocytes are immature red cells released from the bone marrow that circulate in peripheral blood for only 1 to 2 days. Reticulocytes are reported as a percent and as an absolute count. The absolute reticulocyte count is calculated by multiplying the reticulocyte percent by the RBC count. Immature reticulocyte fraction (IRF) is the rate of production of reticulocytes and depends largely on the ability of the bone marrow to respond to erythropoietin.
Two different brands of hematology instruments report reticulocyte hemoglobin content and use different nomenclatures; Ret-He and CHr. Studies have been done that they are equivalent. Reticulocyte hemoglobin (Ret-He) is a direct measurement of the amount of hemoglobin in each reticulocyte, which indicates the amount of iron available for incorporation into erythrocyte hemoglobin. The amount of hemoglobin in reticulocytes also corresponds to the amount that will be present in mature red cells.
Lower than normal hemoglobin content is an indication of inadequate iron supply relative to demand. A low Ret-He can detect early iron deficiency before the development of anemia, microcytosis or hypochromia. Ret-He can also be used to monitor response to iron therapy.
This parameter is particularly important in assessing the iron status of patients receiving recombinant human erythropoietin (r-HuEPO), in whom the cellular requirements for iron are increased. Functional iron deficiency can hamper the effectiveness of r-HuEPO therapy.
The Kidney Disease Outcomes Quality Initiative (KDOQI) has included reticulocyte hemoglobin measurement in its guidelines for assessing the initial iron status of patients with chronic kidney disease on hemodialysis, as well as for monitoring IV iron and r-HuEPO replacement therapy. Studies have shown that reticulocyte hemoglobin <30 pg more accurately predicts functional iron deficiency than the combined use of ferritin <100 ng/mL and transferrin saturation <20%, particularly in patients on chronic hemodialysis who are receiving erythropoietin.
Reticulocyte hemoglobin is reported with the reticulocyte count. Reference range is 30 to 38 pg. A value below 30 pg indicates iron deficient erythropoiesis.
Reference
Brugnara C, Schiller B, Moran J. Reticulocyte hemoglobin equivalent (Ret-He) and assessment of iron-deficient states. Clinical Laboratory Hematology 2006;28:303 – 308.
