Proposal for Percentage Schistocyte Counts in patients with a low or dropping platelet count with schistocytes on blood film.

                                                                   Zini et al, 2012

 I recently reviewed the ICSH recommendations for counting schistocytes in a suspected Thrombotic Microangioapathy and have proposed we do this in our laboratory.

Proposal

To provide a percentage schistocyte count on those films where there is a true thrombocytopenia in conjunction with schistocytes.

The ICSH gives normal reference value of <1 % schistocytes in healthy adults and full term neonates and <5% in premature neonates² .It is suggested that schistocyte counts greater than these values are a robust morphological threshold for suspecting red cell mechanical damage due to thrombotic microangiopathy (TMA). A lack of schistocytes does not rule out a TMA however.

When not to perform a schistocyte count

Schistocytes are seen in a number of conditions and are not specific to TMA. Schistocytes caused by a TMA are usually the dominant feature on the blood film, perhaps in conjunction with moderate signs of stimulated erythropoiesis such as polychromasia, basophilic stippling and nucleated red cells.

If schistocytes are present alongside multiple other red cell abnormalities, the percentage schistocyte count is not appropriate.

Criteria for schistocyte recognition

Schistocytes are defined by the ICSH as always smaller than intact red cells and can have the shape of fragments with sharp angles and straight borders, small crescents, helmet cells, keratocytes, or microspherocytes. Microspherocytes only to be included in the presence of other shapes mentioned¹

Bite cells, spherocytes, irregularly contracted cells, tear drop poikilocytes, and echinocytes should not be included in a schistocyte count.

(See photograph above)

Method

Quantify the schistocytes, only if it they are the dominant abnormality on the film. Not appropriate if they are present alongside multiple other red cell abnormalities.

·         Schistocytes will be counted using a high power x 100 objective.

·         Work out by counting, approximately how many red cells are present per field On a well spread normal film this is approximately 200.

·         In each field count how many schistocytes you see until you have covered 1000 red cells.

·         Express as a percentage of red cells.

Example

Worked out that there are approximately 200 red cells per high power field. Need to count how many fragments are in 10000 red cells. Therefore, five fields of 200 cells will give a total of 10000 red cells.

 

Field 1   200 red cells, 10 schistocytes seen

Field 2   200 red cells, 6 schistocytes seen

Field 3   200 red cells, 8 schistocytes seen

Field 4   200 red cells, 8 schistocytes seen

Field 5   200 red cells, 9 schistocytes seen

 

10+6+8+8+9 = 41 schistocytes seen in a 10000 red cells

 

41  10000 x 100 = a schistocyte count of 4.1%

 

Schistocyte recognition.

a) Keratocyte and helmet cell, b) Schistocyte, c)microspherocyte

Zini et al, 2021

References

1 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.

2 Zini G, d'Onofrio G, Erber WN, Lee SH, Nagai Y, Basak GW, Lesesve JF; International Council for Standardization in Hematology (ICSH). 2021 update of the 2012 ICSH Recommendations for identification, diagnostic value, and quantitation of schistocytes: Impact and revisions. Int J Lab Hematol. 2021 Dec;43(6):1264-1271. doi: 10.1111/ijlh.13682. Epub 2021 Aug 24. PMID: 34431220.