ICSH recommendations for microscopic identification of schistocytes

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 Schistocytes or schizocytes is derived from the greek word ‘schisto’ which means broken or cleft. They are circulating fragments of red blood cells (RBCs) or RBCs which have lost cytoplasmic fragments.

Causes of Schistocytes:

ü  They are usually absent or very rare in healthy individuals

ü  Thrombotic microangiopathy

·         Thrombotic thrombocytopenic purpura

·         Hemolytic uremic syndrome

ü   Malfunctioning prosthetic valve

ü   HELLP syndrome

ü  Malignant hypertension

ü  Metastatic cancer

v  The morphology of RBCs in peripheral smear is important. When schistocytes are seen in non-TMA related genetic or acquired RBC disorders, like Thalassemia, Primary Myelofibrosis, Megaloblastic anemia, thermal injuries, they show marked anisopoikilocytosis and a range of additional RBC size and morphological changes.

Microscopic identification of schistocytes.

According to ICSH, schistocytes are always smaller than intact RBCs

(i)   small fragments of varying shape, with sharp angles or spines (triangles), or straight borders or with a round outline on one side (microcrescents),

usually staining darkly, occasionally pale as a result of loss of hemoglobin at the time of fragmentation

(ii) helmet cells are damaged RBCs with one single, rarely a double, amputated zone highlighted by a straight border, with sharp angulated edges

(iii)  Keratocytes (cells with horns) are damaged cells larger than small fragments having a pair of spicules separated by a semicircular concave segment of membrane

(iv)  Microspherocytes or spheroschizocytes are small-sized hyperdense RBCs with a round shape and increased staining. A pale central zone is absent

·         Microspherocytes are a secondary manifestation of fragmentation and should be included within the schistocyte count only in the presence of the schistocyte shapes mentioned in points (i) to (iii)

·         Caution is that these microspherocytes should not be confused with spherocytes of hereditary spherocytosis or immune hemolysis, which have decreased diameter but are not so small

 Picture below  shows different microscopic forms.

 

Proper microscopic identification of schistocytes is important in treatment and prognostication of TMA. Additional RBC features on smear provide an important clue in differentiating TMA from non-TMA causes.

 

References:

Zini G, d'Onofrio G, Biggs C, et al. ICSH recommendations for identification,diagnostic value, and quantitation of schistocytes. Int J Lab Hematol. 2012;34:107-116.                     

                                                                                              By Dr.Priyavadhana B

 

 

 

 

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