Red Cell Morphology in Disseminated Intravascular Coagulation (DIC)
In Disseminated Intravascular Coagulation (DIC), schistocytes are the characteristic red cell morphology that would be expected. The correct answer is D. Schistocytes.
Pathophysiology of Schistocyte Formation in DIC
Schistocytes (fragmented red blood cells) appear in DIC due to the following mechanisms:
Microvascular thrombosis: In DIC, widespread activation of coagulation leads to fibrin deposition in the microvasculature 1. As red blood cells attempt to pass through these partially occluded vessels, they become fragmented.
Mechanical damage: The presence of fibrin strands in small blood vessels creates a mechanical shearing force that damages passing erythrocytes, resulting in fragmentation 2.
Endothelial injury: According to the International Society on Thrombosis and Haemostasis (ISTH), endothelial injury is an essential component of DIC pathophysiology, contributing to the environment where red cell fragmentation occurs 1.
Characteristics of Schistocytes in DIC
Research specifically examining schistocytes in DIC has found:
Schistocytes are present in approximately 85% of DIC patients (30 out of 35 patients in one study) 2.
The percentage of schistocytes in DIC is typically low, with a mean of 0.33 ± 0.38% and median of 0.1% 2.
Higher schistocyte counts (≥1%) are seen in specific circumstances associated with DIC, such as:
- Acute promyelocytic leukemia
- Pregnancy-related complications
- Severe infections 2
Clinical Significance
While schistocytes are frequently observed in DIC, their measurement is not considered a primary diagnostic test for DIC. The ISTH diagnostic criteria for DIC focus on:
- Platelet count
- Prothrombin time
- Fibrin-related markers (D-dimer)
- Fibrinogen levels 3
However, the presence of schistocytes ≥1% in a patient with suspected DIC might suggest an associated or underlying thrombotic microangiopathy 2.
Other Red Cell Morphologies
The other red cell morphologies listed in the question are not typically associated with DIC:
- Target cells: These are associated with liver disease, hemoglobinopathies, and post-splenectomy states.
- Teardrop cells: These are primarily seen in myelofibrosis and other myeloproliferative disorders.
- Ovalocytes: These are associated with certain hereditary conditions and megaloblastic anemias.
Important Considerations
Schistocytes may not be the only red cell abnormality in DIC. Acanthocytes (spur cells) were actually the most common shape anomaly in one study, present in 22 of 35 DIC patients 2.
The percentage of schistocytes should be interpreted in the context of the clinical presentation and other laboratory findings, as low levels may be within or close to the reference range (<0.5%) 2.
In the diagnostic approach to DIC, the ISTH recommends a two-step approach: initial evaluation using SIC (sepsis-induced coagulopathy) criteria to detect early stages, followed by evaluation for overt DIC using ISTH criteria if SIC is positive 3.