Title:The reticulocyte haemoglobin equivalent (RET-He) and laboratory screening for iron deficiency

Author:C Poffenroth, C Mabbett, C Kendrick.

Abstract:Background: The reticulocyte haemoglobin equivalent (RET_He) parameter provides the haemoglobin (Hb) concentration of peripheral blood reticulocytes on Sysmex Haematology analysers. In the iron deficient (ID) state, reticulocytes and mature red cells have a lower Hb concentration due to the reduced bioavailability of iron. Reticulocyte haemoglobin parameters have been available on cell counting analysers for years. Recently there has been renewed interest surrounding the suitability of the RET_He as a laboratory screening test for ID. This work presents the findings of a study in which the RET_He was evaluated for its use as a marker of ID.
Aim: To establish a reference range for the RET_He and to assess its performance as a laboratory screening test for patient iron deficiency.
Methods: One hundred and seventy-eight patient samples submitted for iron studies to Labcare Pathology and Taranaki MedLab were retested to provide a CBC with a RET_He measurement using the Sysmex XN-2000 (Sysmex, Japan) analyser. All samples had previously been tested for ferritin, serum iron, transferrin and saturation. The results for the RET_He were stratified against iron studies, the CBC results and patient clinical details. A reference range for the RET_He was established using 66 samples from selected patients at Taranaki Base Hospital.
Results: A working cutoff value for ID for the RET_He was established as <26 picograms (pg) of Hb per reticulocyte. Values at or below this cutoff were mainly from patients with either iron deficiency, anaemia of chronic disease or known haemoglobinopathy patients. The reference range for the RET_He with a 95% confidence interval was 30.3- 35.0 pg.
Discussion: This study showed the potential for the use of the RET_He as a simple laboratory screening test for iron deficiency. With a cutoff of <26pg, the RET_He correlated well for red cell microcytosis but was not specific for iron deficiency. Used as a screening test for ID, RET_He results of <26pg could signal the need for iron studies with results above this cutoff acting as a negative predictor of ID in anaemic patients. Used in this way the RET_He could better guide the use of iron studies for patients in whom ID may be suspected.
Keywords: Reticulocyte, RET_He, iron deficiency, anaemia, iron studies.
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