The Clinical Significance of Schistocytes: A Prospective Evaluation of the International Council for Standardization in Hematology Schistocyte Guidelines

OBJECTIVE: The presence of ≥1% schistocytes on a peripheral blood smear (PBS) is an important criterion for the diagnosis of thrombotic microangiopathy (TMA). The reporting of schistocytes has been standardized by the International Council for Standardization in Hematology (ICSH). Despite the availability of guidelines, however, the assessment of schistocytes remains subjective. More recently, the automated fragmented red cell (FRC) parameter has been evaluated. However, local studies are not available. MATERIALS AND METHODS: A prospective study was performed at the Charlotte Maxeke Johannesburg Academic Hospital in order to evaluate the ICSH recommendations for schistocyte measurement in 146 PBSs with schistocytes. Schistocytes were evaluated by microscopy and ADVIA 2120 automated hematology analyzers. RESULTS: Schistocytes were frequently observed in patients with TMA (n=76), infection (n=20), hematologic malignancy (n=10), renal failure (n=5), and hemoglobinopathy (n=15), and in neonates (n=11). Schistocytes were ≥1% in all PBSs with TMA (n=76) with a mean of 3.44±1.84. Schistocytes of ≥1% were also observed in cases of renal failure and hemoglobinopathy, and in neonates. In these conditions, schistocytes were mainly observed in conjunction with moderate red blood cell changes. The agreement between two morphologists gave a correlation coefficient of 0.63 [confidence interval (CI): 0.52-0.75], while the correlation coefficient between the average of the morphologists and the FRC percentage was -1.97 (CI: -1.60 to -2.34). The ADVIA 2120 underestimated the schistocyte count in patients with TMA. CONCLUSION: Observer bias can be decreased by implementing the standardized procedures recommended by the ICSH. However, estimation of schistocytes by the ADVIA 2120 analyzer requires further evaluation as a screening tool. A higher threshold for schistocytes in thrombotic thrombocytopenic purpura is recommended to distinguish this hematological emergency from other conditions associated with ≥1% schistocytes.