Published December 2020 as part of Aculabs’ LabTalk quarterly newsletter.

Aculabs will be offering a Reticulocyte Comprehensive Panel – the panel can provide comprehensive information needed by physicians to assess the rate of red cell production and hemoglobinization. Reticulocyte count (RET #, %) indicates the quantity of circulating reticulocytes. The Immature Reticulocyte Fraction (IRF) indicates the rate of production of reticulocytes and RET-He indicates cell hemoglobinization, the reflecting quality of the newly produced reticulocytes. These three parameters enable “dissociation” of iron-dependent hemoglobinization from erythropoiesis and the tests are rapid and inexpensive to perform.

Reticulocytes are immature red blood cells that circulate in the peripheral blood for 1 to 2 days before becoming red blood cells. They are indicative of effective erythropoiesis and the ability of the bone marrow to produce red blood cells. When there is an increased demand for erythropoiesis, the reticulocytes are released immaturely from the bone marrow. Having the ability to measure the immature reticulocytes and calculate the Immature Reticulocytes Fraction (IRF) will provide the physician with an important tool to assess the bone marrow erythropoietic activity very early on; it can be used to also evaluate and monitor the response to erythropoietin therapy. Additionally, serial monitoring after bone marrow transplant will aid in the assessment of successful engraftment.

One of the other parameters related to the reticulocyte parameter is RET-He or reticulocyte hemoglobin equivalent; it is a test that measures the hemoglobin content of reticulocytes. The RET- He level allows for the diagnosing of anemia before it develops in a patient; it is the first parameter to evaluate iron deficiency in particular and show that the patient is benefiting from the treatment. In cases of iron deficiency, the hemoglobin synthesis is firstly reduced in reticulocytes, making the RET-He the fastest way to detect changes in iron status.

Since red blood cells have a 120-day lifetime, detecting iron deficiencies and changes in the iron status of erythropoiesis is only possible relatively late, using classical parameters such as HGB, MCV, MCH, or chemistry tests like iron, ferritin concentration, total iron-binding capacity (TIBC), and transferrin saturation (TSAT); however, these tests may be influenced by certain conditions. Serum iron can be low due to iron deficiency anemia, as well as in chronic disease anemia, infection, and also fluctuates during the day depending on the iron intake. The fluctuation in iron will cause changes in transferrin saturation since it is calculated based on iron and total iron-binding capacity.

Ferritin levels show the iron deposited in the body, and very low values indicate iron deficiency; however, ferritin is also an acute-phase protein, and levels may appear to be normal or high in cases such as infectious, inflammatory conditions and malignancy. It is also a parameter that can be identified long before the increase in Hb and classical reticulocyte count, which is useful for treatment and follow-up.

– Dr. Rita Khoury

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