DIC vs TTP
How to tell DIC and TTP apart when a board question makes them look alike.
Low fibrinogen with abnormal PT/PTT points DIC; normal fibrinogen/coagulation tests with MAHA points TTP.
Side by side
Bleeding and thrombosis with prolonged PT/PTT, low fibrinogen, high D-dimer, and schistocytes.
Thrombocytopenia and MAHA with neurologic or renal findings but usually normal PT/PTT.
Systemic coagulation activation consumes platelets and clotting factors.
Platelet microthrombi form from ADAMTS13 failure without consuming coagulation factors.
Prolonged PT/PTT and low fibrinogen support DIC.
Normal coagulation studies with schistocytes support TTP.
The trap
Both show schistocytes, thrombocytopenia, and AKI on initial labs, so the smear alone does not split them. The deciding tests are fibrinogen, PT/PTT, and D-dimer: DIC consumes both platelets and clotting factors, so fibrinogen is low and PT/PTT prolonged with markedly elevated D-dimer in a patient with sepsis, OB complication, malignancy, or trauma; TTP consumes only platelets via microvascular thrombi from ADAMTS13 deficiency, so fibrinogen and PT/PTT stay normal. The TTP pentad (fever, microangiopathic hemolytic anemia, thrombocytopenia, AKI, neurologic deficits) needs urgent plasma exchange, not platelet transfusion (transfused platelets feed the thrombi).
Watch it explained
The repair move
When schistocytes appear, check fibrinogen and coagulation tests before choosing DIC or TTP.
Try a free question
CoreA septic patient bleeds from IV sites and has thrombocytopenia, schistocytes, prolonged PT/PTT, low fibrinogen, and high D-dimer. Which diagnosis is most likely?
Show answer and explanation
Answer: A. DIC. Systemic coagulation activation with factor consumption points to DIC.
Why the other choices are tempting
- B. TTP has MAHA and thrombocytopenia but usually normal PT/PTT.
- C. ITP is isolated thrombocytopenia.
- D. Hemophilia prolongs PTT and causes deep bleeding, not factor consumption with high D-dimer.
- E. Vitamin K deficiency prolongs PT/PTT but does not cause schistocyte MAHA.
Flashcards
Tap a card to flip it.
What fibrinogen pattern separates DIC from TTP?
Low fibrinogen supports DIC because clotting factors are being consumed systemically.
Why can DIC prolong PT and PTT?
Diffuse coagulation activation consumes multiple clotting factors, so both pathways can become abnormal.
Quick answers
What is the fastest way to tell DIC from TTP?
Low fibrinogen with abnormal PT/PTT points DIC; normal fibrinogen/coagulation tests with MAHA points TTP.
What is the key clue for DIC?
Bleeding and thrombosis with prolonged PT/PTT, low fibrinogen, high D-dimer, and schistocytes.
What is the key clue for TTP?
Thrombocytopenia and MAHA with neurologic or renal findings but usually normal PT/PTT.
What is the common trap with DIC vs TTP?
Both show schistocytes, thrombocytopenia, and AKI on initial labs, so the smear alone does not split them. The deciding tests are fibrinogen, PT/PTT, and D-dimer: DIC consumes both platelets and clotting factors, so fibrinogen is low and PT/PTT prolonged with markedly elevated D-dimer in a patient with sepsis, OB complication, malignancy, or trauma; TTP consumes only platelets via microvascular thrombi from ADAMTS13 deficiency, so fibrinogen and PT/PTT stay normal. The TTP pentad (fever, microangiopathic hemolytic anemia, thrombocytopenia, AKI, neurologic deficits) needs urgent plasma exchange, not platelet transfusion (transfused platelets feed the thrombi).