Peripheral blood smear

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Author: Mikael Häggström [notes 1]

Look at and comment separately on white blood cells, red blood cells and platelets.

Red blood cells

RDW in adults[1] Terminology[1]
14.5% - 18% Mild anisocytosis
18% - 26% Moderate anisocytosis
> 26% Severe anisocytosis

When available automatic quantification of mean corpuscular volume (MCV) and red blood cell distribution width (RDW), usually as part of CBC panel, generally decides whether you will call the sample "normocytic" versus "microcytic"/"macrocytic" and/or "anisocytotic", even if it is not clearly visible in the microscope. If automated values are not available, compare RBC sizes to lymphocyte nuclei, which should normally be the same size.

Look for poikilocytosis (red blood cells of abnormal shapes):

Schistocytes (fragmented parts red blood cells) only needs mentioning if constituting over 1% of red blood cells or at least 2 per oil immersion field.


If CBC is performed, use count to determine whether platelets are "normal in number" or whether there is "thrombocytopenia" or "thrombocytosis". If no CBC, count platelets within a high power oil immersed field, which should normally be 8 to 20.

In thrombocytopenia from automatic counting, look in particular for clumping of platelets (which can cause a falsely low automatic platelet count). If present, check with the lab if it was sent in EDTA (which may cause artefactual clumping) and ask to have a blood sample sent in sodium citrate instead. Also, look for satellitosis (platelets attached around white blood cells).

White blood cells

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  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.

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  1. 1.0 1.1 . High RDW level in the blood. MrLabTest. Last update: 12/01/2021
  2. Glassy, Eric (1998). Color atlas of hematology : an illustrated field guide based on proficiency testing . Northfield, Ill: College of American Patholgists. ISBN 978-0-930304-66-9. OCLC 40976106.