The key to differentiating between Thrombotic Thrombocytopenic Purpura (TTP) and Disseminated Intravascular Coagulation (DIC) lies primarily in the coagulation profile.
Key Distinctions: Coagulation Profiles
The most significant difference between TTP and DIC is the coagulation profile. This includes several blood tests that evaluate the blood clotting process.
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TTP: Coagulation profile is generally normal. This means that Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) are typically within the normal range. Fibrinogen levels are usually normal or slightly elevated. Fibrin degradation products (FDPs) may be slightly elevated or normal.
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DIC: Coagulation profile is significantly abnormal. You typically see prolonged PT and aPTT, elevated fibrin degradation products (FDPs, including D-dimer), and low fibrinogen levels.
Table Summarizing the Key Differences
| Feature | TTP | DIC |
|---|---|---|
| Coagulation Profile | Generally normal | Prolonged PT & aPTT, elevated FDPs, low fibrinogen |
| PT | Normal | Prolonged |
| aPTT | Normal | Prolonged |
| Fibrinogen | Normal or Slightly Elevated | Low |
| FDPs (D-dimer) | Normal or Slightly Elevated | Elevated |
Other Considerations
While the coagulation profile is crucial, other clinical features can also aid in the differentiation:
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Clinical Setting: DIC often occurs in the setting of severe illness, such as sepsis, trauma, or malignancy. TTP can occur spontaneously or be triggered by medications or autoimmune conditions.
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Schistocytes: Both TTP and DIC can present with schistocytes (fragmented red blood cells) on a peripheral blood smear. Therefore, this finding alone cannot differentiate the two conditions.
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ADAMTS13 Activity: In TTP, ADAMTS13 activity is typically severely deficient (usually <10%). This enzyme is responsible for cleaving von Willebrand factor (vWF). Its deficiency leads to the accumulation of ultra-large vWF multimers, causing platelet aggregation and microthrombi. ADAMTS13 testing is not typically useful for differentiating DIC, as ADAMTS13 activity can be variably affected in DIC.
In Summary
Differentiating between TTP and DIC relies heavily on the coagulation profile. TTP generally presents with a normal coagulation profile, while DIC is characterized by prolonged PT and aPTT, elevated fibrin degradation products, and low fibrinogen levels. ADAMTS13 activity is characteristically low in TTP, whereas clinical context often suggests the diagnosis of DIC.
