Fig. 72.1
Peripheral Smear of DIC
Question
What is the diagnosis?
Answer
Disseminated Intravascular Coagulation (DIC)
Disseminated Intravascular Coagulation (DIC) is a microangiopathic hemolytic anemia (MAHA) characterized by endothelial dysfunction, hemolysis, platelet aggregation, fibrin clot formation, and degradation. After clotting factors and platelets become depleted, bleeding may occur [1]. Because of this simultaneous thrombosis and bleeding, DIC is sometimes referred to as a “consumptive coagulopathy.” The underlying pathophysiology is generally initiated by endothelial or other cell injury, releasing thromboplastic factors which propagate the extrinsic coagulation pathway. This leads to overproduction of thrombin and systemic fibrin, and platelet activation, leading to systemic thrombosis. The simultaneous release of tissue plasminogen activator results in fibrin degradation, contributing to the bleeding diathesis [2]. Depending on the underlying etiology, the onset can be variable ranging from chronic to fulminant. Clinical manifestations of MAHAs include thrombocytopenia, altered mental status, bleeding, myocardial infarction, hemorrhagic/ischemic stroke, renal failure, bowel and limb ischemia, skin necrosis and purpura fulminans (discussed below). The differential diagnosis includes other MAHAs (hemolytic uremic syndrome and thrombotic thrombocytopenic purpura), as well as idiopathic thrombocytopenic purpura, end-stage liver disease, and heparin-induced thrombocytopenia (HIT). The most common underlying etiologies for DIC are sepsis, trauma, both hematologic and solid malignancies, ABO blood mismatch, obstetrical emergencies, and medications (particularly chemotherapeutic agents). Identification of a precipitating event is critical for diagnosis and treatment.
Causes of DIC
Sepsis
Trauma
Hematologic and Solid malignancies
ABO blood mismatch
Obstetrical emergencies
Medications (particularly chemotherapeutic agents)
Envenomation
Principles of Management
Diagnosis
The evaluation of DIC generally includes laboratory investigation of the INR, PTT, platelet count, fibrinogen level, D-dimer and peripheral blood smear. The distinguishing characteristics of DIC are the elevation in both the PT and PTT, with simultaneous reduction of fibrinogen and platelet counts [3]. Although no single laboratory parameter is specific for DIC, this constellation in the proper setting is highly suggestive. Severe derangements in only one or two of these values may suggest an alternative diagnosis. ITP and HIT do not have associated elevation in INR or PTT, while TTP and HUS may sometimes cause elevations. DIC and TTP can have overlapping laboratory features such as elevated LDH, schistocytes and low ADAMTS-13 levels. ADAMTS-13 is a metalloproteinase which cleaves von Willebrand factor and promotes clotting. In DIC, levels can be <30 % of normal while in TTP these are generally <5 % of normal [4]. Liver dysfunction may also confound the diagnosis of DIC, given the constellation of deranged PT/PTT, fibrinogen, and thrombocytopenia. Factor VIII levels may be low in DIC but normal in isolated liver dysfunction. These laboratory values are summarized in Table 72.1. Ultimately, DIC is a clinical diagnosis incorporating history of a causative etiology and characteristic laboratory derangements.
Table 72.1
Patterns of coagulopathy by disorder
INR | PTT | Platelets | Factor VIII | Factor V | ADAMTS-13 | |
---|---|---|---|---|---|---|
DIC | Elevated | Elevated | Low | Low | Low | Low |
HUS/TTP | Normal/elevated | Normal/elevated | Low | Normal/elevated | Normal/elevated | Very low |
Liver | Elevated | Elevated | Low | Low | Normal | Low/Very low |
HIT | Normal | Normal/Elevated | Low | – | – | Low/Very low |
Warfarin | Elevated | Normal | Normal | Normal | Normal | – |
ITP | Normal | Normal | Low | Normal | Normal | Normal |
Heparin | Normal | Elevated | Normal | Normal | Normal | Normal |
Treatment of the Underlying Disorder
The mainstay of therapy for DIC remains treatment of the underlying disorder. Patients with sepsis should be treated with early antibiotics and fluid resuscitation [5]. When malignancy is the underlying cause, chemotherapy, surgical resection, and/or radiation should be pursued to treat the underlying tumor to remove the driving process. In these cases, DIC may worsen as tumor cells are destroyed and leak cytoplasmic contents into the circulation. Care should be given to obstetrical patients to avoid placental damage.
Management of Acute Coagulopathy in Hemorrhaging Patients
Current guidelines caution against blood product administration in DIC patients who are not bleeding. In these non-bleeding patients, AABB guidelines recommend a red cell transfusion threshold of <7 g/dL [6], platelet counts of <10 × 109 cells/L [7], and against fresh frozen plasma (FFP) administration unless the patient is going for surgery or otherwise being massively transfused [8]. In hemorrhaging patients, platelets should be transfused if the count is below 50,000/dL. If the PTT or INR is elevated beyond 1.5, and bleeding is present, FFP may be given [8], though FFP administration may be of little benefit if the INR <1.85 [9]. If the fibrinogen level is <100 g/dL [10] in the setting of hemorrhage, cryoprecipitate should be given.