From the Guidelines
Schistocytes are not always necessary for the diagnosis of hemolytic anemia, but their presence can be critical in certain cases.
Diagnostic Criteria
According to the American Society of Clinical Oncology clinical practice guideline 1, a diagnostic work-up for hemolytic anemia should include a blood smear morphology, where the presence of schistocytes on smear is noted as critical for diagnosis. This is also supported by a more recent update to the guideline 1, which reiterates the importance of blood smear morphology in the diagnostic work-up.
- The presence of schistocytes can indicate microangiopathic changes, which are often seen in conditions such as thrombotic thrombocytopenic purpura (TTP) or hemolytic-uremic syndrome (HUS) 1.
- However, not all cases of hemolytic anemia will present with schistocytes, and other diagnostic criteria such as laboratory tests (e.g. CBC, reticulocyte count, LDH, haptoglobin) and clinical evaluation (e.g. history, physical examination) should also be considered.
Laboratory Tests
In addition to blood smear morphology, other laboratory tests that can aid in the diagnosis of hemolytic anemia include:
- CBC with indices
- Reticulocyte count
- LDH
- Haptoglobin
- Direct antibody test (Coombs test) These tests can help to identify the underlying cause of the hemolytic anemia and guide further management.
From the Research
Diagnosis of Hemolytic Anemia
- The presence of schistocytes is an important morphological clue to the diagnosis of thrombotic microangiopathic anemia (TMA) 2.
- However, the detection of schistocytes is not exclusive to TMA and can be observed in various diseases, such as microangiopathic hemolytic anemia (MAHA), metastatic carcinoma, sepsis, chronic renal failure, preterm infant, and infection 3.
- Schistocytes can be absent in some cases of thrombotic thrombocytopenic purpura (TTP), emphasizing the need to consider TTP-hemolytic uremic syndrome in the differential diagnosis even in the absence of peripheral schistocytosis 4.
Role of Schistocytes in Diagnosis
- A schistocyte count has a definite clinical value for the diagnosis of TMA in the absence of additional severe red cell shape abnormalities, with a confident threshold value of 1% 2.
- The presence of schistocytes below a threshold determined at 1% had a negative predictive value close to 100% to exclude the presence of schistocytes on the blood smear 5.
- Schistocytes are not necessary for the diagnosis of hemolytic anemia, as they can be observed in a broader spectrum of disorders than TTP/hemolytic uremic syndrome, or might be delayed even absent 6.
Automated Measurement of Schistocytes
- Automated counting of RBC fragments is recommended by the ICSH Working Group as a useful complement to the microscope, according to the high predictive value of negative results 2.
- The FRC parameter on automated blood cell counters (ABCC) can be used to exclude schistocytes and the diagnosis of TMA, with a reference range of <0.3% for the ADVIA and <0.5% for the XE-2100 5.