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Usefulness of reporting RBC morphology.

Q Can you comment on the usefulness of reporting red-blood-cell (RBC) morphology on specimens submitted for a complete blood count (CBC), as opposed to a CBC with differential? We are currently scanning a slide for any specimen with RBC distribution width (RDW) <11.0 or >17.0 or "other abnormal indices," or unusual RBC/hemoglobin (HGB) ratio. Are these guidelines clinically useful? Also, I am wondering about the correlation between indices and morphology. Is it usual to see hypochromia with a normal mean cell hemoglobin concentration (MCHC) or microcytosis with a normal mean cell volume (MCV)?

A There are certainly instances where a morphologic assessment of the red cells is useful, even if a differential is not ordered. Notably, the presence of spherocytes (hemolysis), teardrop cells (myelofibrosis, bone marrow metastases), or sickle cells (sickle-cell anemia), as examples, give information beyond that of the standard indices. Abnormal indices can give a clue to these morphologic abnormalities, so having some parameters in place is useful. An unusual RBC/HGB ratio may highlight patients with both anemia and an elevated RBC count, such as those with a hemoglobin disorder, including thalassemia. In general, a smear review for an increased RDW (such as >17.0) could be very useful, as it may show dimorphic populations and other abnormal red-cell morphology, which provide important clinical information. A low RDW (<11.0), which would indicate a more uniformly sized RBC population, however, is not clinically significant.

There is a correlation between indices and morphology. The instrument is very accurate, especially for size (MCV) and variation in size (RDW), since it looks at many more red cells than a morphologic assessment alone and evaluates them in their three-dimensional configuration. But that does not mean the instrument is perfect. The instrument would not detect any red-cell inclusions, such as Howell-Jolly bodies, basophilic stippling, and Pappenheimer bodies. It may also have trouble detecting a minor abnormal population. The MCV may be normal in these situations, but a subpopulation of microcytic cells may be present. Correlating the MCV with the other RBC indices is extremely helpful in these situations, such as in increased RDW, reflecting the increased spectrum of cell size. Finally, the usefulness of morphology in these cases depends on your patient population. If you have a diverse population that includes patients of many different ethnic backgrounds, there may be more usefulness to these analyses.

--Kathleen Siechen, MD

--Guang Fan, MD, PhD

Hematology Service

Department of Pathology

Oregon Health and Sciences University

Portland, OR
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Title Annotation:Answering your questions; red-blood-cell
Author:Siechen, Kathleen; Fan, Guang
Publication:Medical Laboratory Observer
Article Type:Column
Geographic Code:1USA
Date:Nov 1, 2007
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