The differential diagnosis includes the following: thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura, disseminated intravascular coagulation, and heparin-induced thrombocytopenia.

The most likely diagnosis in this clinical setting is disseminated intravascular coagulation (DIC). DIC is a syndrome, not a diagnosis. It is an acquired state that occurs as a result of a number of underlying conditions (Table 51-1). For the purpose of this chapter, we will focus on acute DIC. In the setting of DIC, there is global activation of the coagulation system with formation of fibrin within the circulation. Fibrin deposition leads to thrombosis and occlusion of small vessels, with subsequent end-organ damage. At the same time, depletion of platelets and clotting factors can also lead to bleeding.¹

In the clinical scenario described above, DIC may be due to his traumatic brain injury (TBI) as well as his sepsis. The brain has a high concentration of tissue thromboplastin, which has a tendency to become prothrombotic when released into systemic circulation.² DIC has been described in a signification proportion of patients with TBI and is associated with increased morbidity and mortality. He is also bacteremic. Sepsis may cause marked activity of the inflammatory system, and inflammation-induced activation of coagulation is a well-recognized phenomenon.³ Severe sepsis may be complicated by DIC in about 35% of cases.⁴

DIC is a clinical diagnosis of a syndrome. Clinical manifestations include:⁵

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  Thrombosis

  
  
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  Bleeding

  
  
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  Renal dysfunction

  
  
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  Hepatic dysfunction

  
  
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  Shock

On physical examination one may note cool, mottled extremities; petechiae; ecchymoses; or hemorrhages at the site of invasive procedures. From a laboratory standpoint, there is not one single laboratory test in isolation that can determine the diagnosis of DIC. Instead, DIC is a clinical syndrome, and laboratory data help support clinical suspicion (Table 51-2).

It is important to remember to monitor the trend in these parameters. As fibrinogen is an acute-phase reactant, it can be elevated in the setting of sepsis or inflammation. Therefore, evaluating serial measurements and analyzing the trend are essential. A review of the peripheral smear may reveal the presence of microangiopathic changes.