Disseminated Intravascular Coagulation (DIC)
The most likely diagnosis is diffuse intravascular coagulation (DIC), given the constellation of fever, hypotension (suggesting sepsis or severe systemic illness), thrombocytopenia, elevated D-dimer, normochromic normocytic anemia, and schistocytes on peripheral blood smear. 1, 2
Clinical Reasoning and Diagnostic Approach
Key Diagnostic Features Present
This patient demonstrates the classic pentad of DIC:
Fever (39.5°C) with hypotension (90/60 mmHg): Suggests an underlying trigger such as sepsis, which is the most common cause of acute DIC through pathological activation of the intrinsic coagulation system 1
Thrombocytopenia with recent bruising: Reflects platelet consumption in the systemic coagulation process, a hallmark of decompensated DIC 1, 2
Elevated D-dimer: Indicates both thrombin generation (coagulation activation) and plasmin generation (fibrinolysis), which is characteristic of DIC 2, 3
Schistocytes on peripheral blood smear: While schistocytes are frequently observed in DIC patients (found in 30 of 35 DIC patients in one study), they typically appear in low percentages (mean 0.33%, median 0.1%) 4
Normochromic, normocytic anemia: Consistent with acute hemolysis and the consumptive process of DIC 5
Diagnostic Confirmation
DIC is diagnosed by finding abnormalities in at least 3 of 4 laboratory values: prothrombin time, platelet count, fibrinogen, and fibrinogen/fibrin degradation products. 1 This patient already has confirmed thrombocytopenia and elevated D-dimer (a fibrin degradation product), satisfying at least 2 criteria.
The combination of D-dimer and FDP testing offers the highest diagnostic efficiency (95%) with 91% sensitivity and 94% specificity for DIC. 3
Excluding Alternative Diagnoses
Why not the other options:
Intermediate beta thalassemia (option a): Would present with microcytic anemia, not normocytic, and would not explain the acute presentation with fever, hypotension, thrombocytopenia, or elevated D-dimer 5
Megaloblastic anemia (option c): Presents with macrocytic anemia, not normocytic, and does not cause thrombocytopenia, schistocytes, or elevated D-dimer in this acute context 5
Cold-type autoimmune hemolytic anemia (option d): Would not explain the fever, hypotension, thrombocytopenia, or elevated D-dimer; schistocytes are not a typical feature 5
Paroxysmal nocturnal hemoglobinuria (option e): Can cause thrombosis and hemolysis but typically presents with hemoglobinuria, pancytopenia in chronic settings, and would not explain the acute septic picture with fever and hypotension 5
Critical Diagnostic Pitfall
A common pitfall is confusing DIC with thrombotic thrombocytopenic purpura (TTP) or hemolytic-uremic syndrome (HUS), both of which present with microangiopathic hemolytic anemia and schistocytes. 6 However, the key distinguishing feature is that DIC presents with elevated D-dimer and abnormal coagulation studies (PT/PTT), while TTP/HUS typically have normal coagulation parameters. 7, 2 The presence of fever with hypotension strongly suggests an infectious/septic trigger for DIC rather than TTP. 5
Additional Testing Needed
To confirm DIC and guide management:
- Prothrombin time (PT) and partial thromboplastin time (PTT): Expected to be prolonged in DIC 1, 3
- Fibrinogen level: Expected to be decreased due to consumption 1, 2
- Blood cultures: To identify the underlying septic trigger 5
- Peripheral blood smear review: Already shows schistocytes; look for percentage (≥1% suggests associated thrombotic microangiopathy) 4
Clinical Context
The finding of minimally elevated ESR in the setting of severe clinical disease should prompt investigation for DIC, as noted in Kawasaki disease guidelines, though this principle applies broadly. 5 The presence of schistocytes ≥1% in DIC patients often indicates circumstances associated with increased schistocyte counts such as severe infection, which fits this clinical picture. 4
Coagulation abnormalities in DIC can include prolongations of PTT or PT, and cases of disseminated intravascular coagulation have been described that led to death. 5 This underscores the urgency of diagnosis and treatment.