INTRODUCTION

In the normal person, the process of coagulation is finely controlled at many levels to ensure the appropriate amount of hemostasis at the appropriate location. Broadly defined, disseminated intravascular coagulation (DIC) is the name given to any process that disrupts this fine tuning, leading to unregulated coagulation. Defined this way, DIC may be found in a variety of patients with a variety of disease states, and can present with a spectrum of findings ranging from asymptomatic abnormal laboratory results to florid bleeding or thrombosis. It is important to remember that DIC is always a consequence of an underlying pathological process and not a disease in and of itself. This article first reviews concepts common to all forms of DIC, and then reviews the more common disease states that lead to DIC.

PATHOGENESIS

At the most basic level, DIC is the clinical manifestation of inappropriate thrombin activation.^1–5 Inappropriate thrombin activation can be due to underlying conditions such as sepsis and obstetric disasters. The activation of thrombin leads to (1) conversion of fibrinogen to fibrin, (2) activation of platelets (and their consumption), (3) activation of factors V and VIII, (4) activation of protein C (and degradation of factors Va and VIIIa), (5) activation of endothelial cells, and (6) activation of fibrinolysis (Table 1).

Thus, with excessive activation of thrombin one can see the following processes:

1. Conversion of fibrinogen to fibrin, which leads to the formation of fibrin monomers and excessive thrombus formation. These thrombi are rapidly dissolved by excessive fibrinolysis in most patients. In certain clinical situations, especially cancer, excessive thrombosis will occur. In patients with cancer, this is most often a deep venous thrombosis. Rare patients, especially those with pancreatic cancer, may have severe DIC with multiple arterial and venous thromboses. Nonbacterial thrombotic endocarditis can also be seen in these patients, leading to widespread embolic complications.

2. Activation of platelets and their consumption. Thrombin is the most potent physiologic activator of platelets, so in DIC there is increased activation of platelets. These activated platelets are consumed, resulting in thrombocytopenia. Platelet dysfunction is also present. Platelets that have been activated and have released their contents but still circulate are known as “exhausted” platelets; these cells can no longer function to support coagulation. The fibrin degradation products (FDP) in DIC can also bind to GP IIb/IIIa and inhibit further platelet aggregation.

3. Activation of factors V, VIII, XI, and XIII. Activation of these factors can promote thrombosis, but they are then rapidly cleared by antithrombin (XI) or activated protein C (V and VIII) or by binding to the fibrin clot (XIII). This can lead to depletion of all the prothrombotic clotting factors and antithrombin, which in turn can lead to both thrombosis and bleeding.

4. Activation of protein C further promotes degradation of factors Va and VIIIa, enhances fibrinolysis, and decreases protein C levels.

5. Activation of endothelial cells, especially in the skin, may lead to thrombosis, and in certain patients, especially those with meningococcemia, purpura fulminans. Endothelial damage will down-regulate thrombomodulin, preventing activation of protein C and leading to further reductions in levels of activated protein C.⁵6. Activation of fibrinolysis leads to the breakdown of fibrin monomers, formation of fibrin thrombi, and increased circulating fibrinogen. In most patients with DIC, the fibrinolytic response is brisk.⁶ This is why most patients with DIC present with bleeding and prolonged clotting times.

PATTERNS OF DIC

The clinical manifestations of DIC in a given patient depend on the balance of thrombin activation and secondary fibrinolysis plus the patient’s ability to compensate for the DIC. Patients with DIC can present in 1 of 4 patterns:^1–3

1. Asymptomatic. Patients can present with laboratory evidence of DIC but no bleeding or thrombosis. This is often seen in patients with sepsis or cancer. However, with further progression of the underlying disease, these patients can rapidly become symptomatic.

2. Bleeding. The bleeding is due to a combination of factor depletion, platelet dysfunction, thrombocytopenia, and excessive fibrinolysis.¹ These patients may present with diffuse bleeding from multiple sites (eg, intravenous sites, areas of instrumentation).

3. Thrombosis. Despite the general activation of the coagulation process, thrombosis is unusual in most patients with acute DIC. The exceptions include patients with cancer, trauma patients, and certain obstetrical patients. Most often the thrombosis is venous, but arterial thrombosis and nonbacterial thrombotic endocarditis have been reported.⁷

4. Purpura fulminans. This form of DIC is discussed in more detail later (see Specific DIC Syndromes section).

DIAGNOSIS

There is no one test that will diagnose DIC; one must match the test to the clinical situation (Table 2).⁸

SCREENING TESTS

The prothrombin time-INR and activated thromboplastin time (aPPT) are usually elevated in severe DIC but may be normal or shortened in chronic forms.⁹ One may also see a shortened aPTT in severe acute DIC due to large amounts of activated thrombin and factor X “bypassing” the contact pathway. An aPTT as short as 10 seconds has been seen in acute DIC. The platelet count is usually reduced but may be normal in chronic DIC. Serum fibrinogen and platelets are decreased in acute DIC but again may be in the “normal” range in chronic DIC.¹⁰ The most sensitive screening test for DIC is a fall in the platelet count, with low counts seen in 98% of patients and counts under 50,000 cells/μL in 50%.^9,11 The least specific test is fibrinogen, which tends to fall below normal only in severe acute DIC.⁹

SPECIFIC TESTS

This group of tests allows one to deduce that abnormally high concentrations of thrombin are present.

Ethanol Gel and Protamine Tests

Both of these older tests detected circulating fibrin monomers, whose appearance is an early sign of DIC. Circulating fibrin monomers are seen when thrombin acts on fibrinogen. Usually the monomer polymerizes with the fibrin clot, but when there is excess thrombin these monomers can circulate. Detection of circulating fibrin monomer means there is too much IIa and, ergo, DIC is present.

Fibrin(ogen) Degradation Products

Plasmin acts on the fibrin/fibrinogen molecule to cleave the molecule in specific places. The resulting degradation product levels will be elevated in situations of increased fibrin/fibrinogen destruction (DIC and fibrinolysis). The FDP are typically mildly elevated in renal and liver disease due to reduced clearance.

D-Dimers

When fibrin monomers bind to form a thrombus, factor XIII acts to bind their “D” domains together. This bond is resistant to plasmin and thus this degradation fragment is known as the “D-dimer.” High levels of D-dimer indicate that (1) IIa has acted on fibrinogen to form a fibrin monomer that bonded to another fibrin monomer, and (2) this thrombus was lysed by plasmin. Because D-dimers can be elevated (eg, with exercise, after surgery), an elevated D-dimer needs to be interpreted in the context of the clinical situation.¹¹ Currently, this is the most common specific test for DIC performed.

Other Tests

Several other tests are sometimes helpful in diagnosing DIC.

Thrombin time. This test is performed by adding thrombin to plasma. Thrombin times are elevated in DIC (FDPs interfere with polymerization), in the presence of low fibrinogen levels, in dysfibrinogenemia, and in the presence of heparin (very sensitive).

Reptilase time is the same as thrombin time but is performed with a snake venom that is insensitive to heparin. Reptilase time is elevated in the same conditions as the thrombin time, with the exception of the presence of heparin. Thrombin time and reptilase time are most useful in evaluation of dysfibrinogenemia.

Prothrombin fragment 1.2 (F_1.2). F_1.2is a small peptide cleaved off when prothrombin is activated to thrombin. Thus, high levels of F_1.2 are found in DIC but can be seen in other thrombotic disorders. This test is still of limited clinical value.

DIC scoring system. A scoring system to both diagnose and quantify DIC has been proposed (Figure).^11,12

This system is especially helpful for clinical trials. A drawback of the score that keeps it from being implemented for routine clinical use is that it requires the prothrombin time, which is not standardized nor often reported by many clinical laboratories.

Thromboelastography (TEG). This is a point-of-care test that uses whole blood to determine specific coagulation parameters such as R time (time from start of test to clot formation), maximal amplitude (MA, maximum extent of thrombus), and LY30 (MA at 30 minutes, a measure of fibrinolysis).¹³ Studies have shown that TEG can identify DIC by demonstrating a shorter R time (excess thrombin generation) which prolongs as coagulation factors are consumed. The MA is decreased as fibrinogen is consumed and the LY30 shows excess fibrinolysis. TEG has been shown to be of particular value in the management of the complex coagulopathy of trauma.¹⁴

MIMICKERS OF DIC

It is important to recognize coagulation syndromes that are not DIC, especially those that have specific other therapies. The syndromes most frequently encountered are thrombotic thrombocytopenic purpura (TTP) and catastrophic antiphospholipid antibody syndrome (CAPS). One important clue to both of these syndromes is that, unlike DIC, there is no primary disorder (cancer, sepsis) that is driving the coagulation abnormalities.

TTP should be suspected when any patient presents with any combination of thrombocytopenia, microangiopathic hemolytic anemia (schistocytes and signs of hemolysis) plus end-organ damage.^15–18 Patients with TTP most often present with intractable seizures, strokes, or sequelae of renal insufficiency. Many patients who present with TTP have been misdiagnosed as having sepsis, “lupus flare,” or vasculitis. The key diagnostic differentiator between TTP and DIC is the lack of activation of coagulation with TTP—fibrinogen is normal and D-dimers are minimally or not elevated. In TTP, lactate dehydrogenase is invariably elevated, often 2 to 3 times normal.¹⁹ The importance of identifying TTP is that untreated TTP is rapidly fatal. Mortality in the pre–plasma exchange era ranged from 95% to 100%. Today plasma exchange therapy is the foundation of TTP treatment and has reduced mortality to less than 20%.^16,20–23Rarely patients with antiphospholipid antibody syndrome can present with fulminant multiorgan system failure.^24–28 CAPS is caused by widespread microthrombi in multiple vascular fields. These patients will develop renal failure, encephalopathy, adult respiratory distress syndrome (often with pulmonary hemorrhage), cardiac failure, dramatic livedo reticularis, and worsening thrombocytopenia. Many of these patients have pre-existing autoimmune disorders and high-titer anticardiolipin antibodies. It appears that the best therapy for these patients is aggressive immunosuppression with steroids plus plasmapheresis, followed by rituximab or, if in the setting of lupus, intravenous cyclophosphamide monthly.^27,29 Early recognition of CAPS can lead to quick therapy and resolution of the multiorgan system failure.

GENERAL THERAPY

The best way to treat DIC is to treat the underlying cause that is driving the thrombin generation.^1,2,4,30,31 Fully addressing the underlying cause may not be possible or may take time, and in the meantime it is necessary to disrupt the cycle of thrombosis and/or hemorrhage. In the past, there was concern about using factor replacement due to fears of “feeding the fire,” or perpetuating the cycle of thrombosis. However, these concerns are not supported by evidence, and factors must be replaced if depletion occurs and bleeding ensues.³²

Transfusion therapy of the patient with DIC is guided by the 5 laboratory tests that reflect the basic parameters essential for both hemostasis and blood volume status:^33,34 hematocrit, platelet count, prothrombin time-INR, aPTT, and fibrinogen level. Decisions regarding replacement therapy are based on the results of these laboratory tests and the clinical situation of the patient (Table 3).

The transfusion threshold for a low hematocrit depends on the stability of the patient. If the hematocrit is below 21% and the patient is bleeding or hemodynamically unstable, packed red cells should be transfused. Stable patients can tolerate lower hematocrits and an aggressive transfusion policy may be detrimental.^35–37 In DIC, due to both the bleeding and platelet dysfunction, keeping the platelet count higher than 50,000 cells/μL is reasonable.^33,38 The dose of platelets to be transfused should be 6 to 8 platelet concentrates or 1 plateletpheresis unit. In patients with a fibrinogen level less than 150 mg/dL, transfusion of 10 units of cryoprecipitate is expected to increase the plasma fibrinogen level by 150 mg/dL. In patients with an INR greater than 2 and an abnormal aPTT, 2 to 4 units of fresh frozen plasma (FFP) can be given.³¹ For an aPTT greater than 1.5 times normal, 4 units of plasma should be given. Elevation of the aPTT above 1.8 times normal is associated with bleeding in trauma patients.³⁹ Patients with marked abnormalities, such as an aPTT increased 2 times normal, may require aggressive therapy with at least 15 to 30 mL/kg (4–8 units for an average adult) of plasma.⁴⁰

The basic 5 laboratory tests should be repeated after administering the blood products. This allows one to ensure that adequate replacement therapy was given for the coagulation defects. Frequent checks of the coagulation tests also allow rapid identification and treatment of new coagulation defects in a timely fashion. A flow chart of the test and the blood products administered should also be maintained. This is important in acute situations such as trauma or obstetrical bleeding.

In theory, since DIC is the manifestation of exuberant thrombin production, blocking thrombin with heparin should decrease or shut down DIC. However, studies have shown that in most patients heparin administration has led to excessive bleeding. Currently, heparin therapy is reserved for patients who have thrombosis as a component of their DIC.^2,41,42 Given the coagulopathy that is often present, specific heparin levels instead of the aPTT should be used to monitor anticoagulation.^43,44

SPECIFIC DIC SYNDROMES

SEPSIS/INFECTIOUS DISEASE

Any overwhelming infection can lead to DIC.⁴⁵ Classically, it was believed that gram-negative bacteria can lead tissue factor exposure via production of endotoxin, but recent studies indicate that DIC can be seen with any overwhelming infection.^46,47 There are several potential avenues by which infections can lead to DIC. As mentioned, gram-negative bacteria produce endotoxin that can directly lead to tissue factor exposure, resulting in excess thrombin generation. In addition, any infection can lead to expression of inflammatory cytokines that induce tissue-factor expression by endothelium and monocytes. Some viruses and Rickettsia species can directly infect the vascular endothelium, converting it from an antithrombotic to a prothrombotic phenotype.⁴⁸ When fighting infections, neutrophils can extrude their contents, including DNA, to help trap organisms. These neutrophil extracellular traps (NETS) may play an important role in promoting coagulopathy.^49,50 The hypotension produced by sepsis leads to tissue hypoxia, which results in more DIC. The coagulopathy in sepsis can range from subtle abnormalities of testing to purpura fulminans. Thrombocytopenia is worsened by cytokine-induced hemophagocytic syndrome.

As with all forms of DIC, empiric therapy targeting the most likely source of infection and maintaining hemodynamic stability is the key to therapy. As discussed below, heparin and other forms of coagulation replacement appear to be of no benefit in therapy.

PURPURA FULMINANS

DIC in association with necrosis of the skin is seen in primary and secondary purpura fulminans.^51,52 Primary purpura fulminans is most often seen after a viral infection.⁵³ In these patients, the purpura fulminans starts with a painful red area on an extremity that rapidly progresses to a black ischemic area. In many patients, acquired deficiency of protein S is found.^51,54,55 Secondary purpura fulminans is most often associated with meningococcemia infections but can be seen in any patient with overwhelming infection.^56–58Post-splenectomy sepsis syndrome patients and those with functional hyposplenism due to chronic liver diseases are also at risk.⁵⁹ Patients present with signs of sepsis, and the skin lesions often involve the extremities and may lead to amputations. As opposed to primary purpura fulminans, those with the secondary form will have symmetrical ischemia distally (toes and fingers) that ascends as the process progresses. Rarely, adrenal infarction (Waterhouse-Friderichsen syndrome) occurs, which leads to severe hypotension.⁴⁵

Recently, Warkenten has reported on limb gangrene in critically ill patients complicating sepsis or cardiogenic shock.^60,61 These patients have DIC that is complicated by shock liver. Deep venous thrombosis with ischemic gangrene then develops, which can result in tissue loss and even amputation. The pathogenesis is hypothesized to be hepatic dysfunction leading to sudden drops in protein C and S plasma levels, which then leads to thrombophilia with widespread microvascular thrombosis. Therapy for purpura fulminans is controversial. Primary purpura fulminans, especially in those with postvaricella autoimmune protein S deficiency, has responded to plasma infusion titrated to keep the protein S level above 25%.⁵¹ Intravenous immunoglobulin has also been reported to help decrease the anti-protein S antibodies. Heparin has been reported to control the DIC and extent of necrosis.⁶² The starting dose in these patients is 5 to 8 units/kg/hr.²

Sick patients with secondary purpura fulminans have been treated with plasma drips, plasmapheresis, and continuous plasma ultrafiltration.^62–66Heparin therapy alone has not been shown to improve survival.⁶⁶ Much attention has been given to replacement of natural anticoagulants such as protein C and antithrombin as therapy for purpura fulminans, but unfortunately randomized trials using antithrombin have shown mostly negative results.^{51,55,67–69} Trials using protein C concentrates have shown more promise in controlling the coagulopathy of purpura fulminans, but this is not widely available.^63,70–72 Unfortunately, many patients will need debridement and amputation for their necrotic limbs, with one review showing approximately 66% of patients needing amputations.⁵²

TRAUMA

Currently, the most common cause of acute DIC is trauma. The coagulation defects that occur in trauma patients are complex in origin and still controversial (including if even calling it DIC is appropriate!).^73–76 The most common etiologies are

Generation of excess activated protein C leading to increased consumption of factor V and VIII and increased fibrinolysis;
Tissue damage leading to generation of excess thrombin generation;
Dilution of hemostatic factors by blood or fluid resuscitation; and
Activation of endothelial cells leading to generation of a prothrombotic surface and shedding of glycocalyx with antithrombotic properties.

Trauma patients are prone to hypothermia, and this can be the major complicating factor in their bleeding.^77,78 Patients may be out “in the field” for a prolonged period of time and be hypothermic on arrival.⁷⁹ Packed red cells are stored at 4°C, and the infusion of 1 unit can lower the body temperature by 0.16°C.⁸⁰ Hypothermia has profound effects on the coagulation system that are associated with clinical bleeding.^77,81,82 Even modest hypothermia can greatly augment bleeding and needs to be treated or prevented.

The initial management of the bleeding trauma patient is administration of red cells and plasma (FFP) in a 1:1 ratio. This has been shown by clinical studies to lessen the risk of exsanguination in the first 24 hours and to be associated with improved clinical outcomes.^83,84The basic set of coagulation tests should also be obtained to guide product replacement, especially as the bleeding is brought under control. Hypothermia can be prevented by several measures, including transfusing the blood through blood warmers. Devices are available that can warm 1 unit of blood per minute. An increasingly used technique is to perform “damage control” surgery. Patients are initially stabilized with control of damaged vessels and packing of oozing sites.⁸⁵ Then the patient is taken to the intensive care unit to be warmed and have coagulation defects corrected.

For trauma patients at risk of serious bleeding, the use of tranexamic acid reduced all- cause mortality (relative risk 0.91), with death due to bleeding also being reduced (relative risk 0.85).⁸⁶ There was no increase in thrombosis, but benefit was restricted to patients treated within 3 hours of the trauma. The dose of tranexamic acid was a 1-g bolus followed by a 1-g continuous infusion over 8 hours.

PREGNANCY-RELATED DIC SYNDROMES

Acute DIC of Pregnancy

Pregnancy can be associated with the rapid onset of severe DIC in 2 situations, abruption and amniotic fluid embolism.^87,88 The separation of the placenta from the uterine wall creates a space for blood to occupy. Given the richness of the placenta in tissue factor, this leads to activation of coagulation both locally and systemically. Release of blood when this space reaches the vaginal opening can lead to rapid hemorrhage, further augmenting the coagulation abnormalities. Placental insufficiency can lead to fetal demise, which can also worsen the DIC. Management depends on the size of the abruption and the clinical status of both mother and fetus.⁸⁷ For severe bleeding and DIC, blood product support is crucial to allow safe delivery. In pregnancy, the fibrinogen goal needs to be higher—200 mg/dL.⁸⁹ For smaller abruption, close observation with early delivery is indicated.

Amniotic fluid embolism is sudden, with the vascular collapse of the woman soon after delivery. Due to the presence of procoagulant rich fluid in the circulatory system, there is often overwhelming DIC. Therapy is directed at both supporting blood volume and correcting hemostatic defects.

HELLP

The acronym HELLP (hemolysis, elevated liver tests, low platelets) describes a variant of preeclampsia.⁹⁰ Classically, HELLP syndrome occurs after 28 weeks of gestation in a patient with preeclampsia, but can occur as early as 22 weeks in patients with antiphospholipid antibody syndrome.^91–93 The preeclampsia need not be severe. The first sign of HELLP is a decrease in the platelet count followed by abnormal liver function tests. Signs of hemolysis are present with abundant schistocytes on the smear and a high lactate dehydrogenase level. HELLP can progress to liver failure, and deaths are also reported due to hepatic rupture. Unlike TTP, fetal involvement is present in the HELLP syndrome, with fetal thrombocytopenia reported in 30% of cases. In severe cases, elevated D-dimers consistent with DIC are also found. Delivery of the child will most often result in cessation of the HELLP syndrome, but refractory cases will require dexamethasone and plasma exchange.⁹⁴ Patients should be closely observed for 1 to 2 days after delivery as the hematologic picture can transiently worsen before improving.⁹⁵

Acute Fatty Liver of Pregnancy

Fatty liver of pregnancy also occurs late in pregnancy and is only associated with preeclampsia in 50% of cases.^96,97 Patients first present with nonspecific symptoms of nausea and vomiting but can progress to fulminant liver failure. Patients develop thrombocytopenia early in the course, but in the later stages can develop DIC and very low fibrinogen levels. Mortality rates without therapy can be as high as 90%. Low blood glucose and high ammonia levels can help distinguish fatty liver from other pregnancy complications.⁹⁸ Treatment consists of prompt delivery of the child and aggressive blood product support.

Retained Dead Fetus Syndrome

Becoming rarer in modern practices, the presence of a dead fetus for many weeks (usually ≥ 5) can result in a chronic DIC state with fibrinogen depletion and coagulopathy. In some women, this is worsened at delivery. In a stable patient, a short trial of heparin prior to planning delivery can control the DIC to allow the coagulopathy to stabilize.

DRUG-INDUCED HEMOLYTIC-DIC SYNDROMES

A severe variant of the drug-induced immune complex hemolysis associated with DIC has been recognized. Rare patients who receive certain second- and third-generation cephalosporins (especially cefotetan and ceftriaxone) have developed this syndrome.^99–104 The clinical syndrome starts 7 to 10 days after the drug is administered. Often the patient has only received the antibiotic for surgical prophylaxis. The patient will develop severe Coombs’-positive hemolysis with hypotension and DIC. The patients are often believed to have sepsis and in the management of the supposed sepsis often are re-exposed to the cephalosporin, resulting in worsening of the clinical picture. The outcome is often fatal due to massive hemolysis and thrombosis.^{101,105–107}

Quinine is associated with a unique syndrome of drug-induced DIC.^108–111 Approximately 24 to 96 hours after quinine exposure, the patient becomes acutely ill with nausea and vomiting. The patient then develops a microangiopathic hemolytic anemia, DIC, and renal failure. Some patients, besides having antiplatelet antibodies, also have antibodies binding to red cells and neutrophils, which may lead to the more severe syndrome. Despite therapy, patients with quinine-induced TTP have a high incidence of chronic renal failure.

Treatment of the drug-induced hemolytic-DIC syndrome is anecdotal. Patients have responded to aggressive therapy, including plasma exchange, dialysis, and prednisone. Early recognition of the hemolytic anemia and the suspicion it is drug related is important for early diagnosis so that the incriminated drug can be discontinued.

CANCER

Cancers, primarily adenocarcinomas, can result in DIC. The classic Trousseau syndrome referred to the association of migratory superficial thrombophlebitis with cancer¹¹² but now refers to cancer associated with thrombotic DIC.^113,114 Highly vascular tumor cells are known to express tissue factor.^114,115 In addition, some tumor cells can express a direct activator of factor X (“cancer procoagulant”). Unlike many DIC states, cancer presents with thrombosis instead of bleeding. This may be due to the inflammatory state which accompanies cancer, or it may be a unique part of the chronic nature of cancer DIC biology that allows time for the body to compensate for loss of coagulation factors. In some patients, thrombosis is the first sign of an underlying cancer, sometimes predating the cancer diagnosis by months.¹¹⁵ Rarely, the DIC can result in nonthrombotic endocarditis with micro-emboli leading to widespread small-vessel thrombosis.¹¹³

Since effective antineoplastic therapy is lacking for many tumors associated with Trousseau syndrome, DIC therapy is aimed at suppressing thrombosis. An exception is prostate cancer, where hormonal therapy can markedly decrease the DIC.¹¹⁶Due to the tumor directly activating coagulation factors, inhibition of active enzymes via heparin has been shown to reduce rates of recurrence compared with warfarin.^114,115 Clinical trials have demonstrated that heparin therapy is associated with a lower thrombosis recurrence rate than warfarin.^117,118 In some patients, the thrombotic process is so vigorous that new thrombosis can be seen within hours of stopping heparin.¹¹²

ACUTE PROMYELOCYTIC LEUKEMIA

There are multiple hemostatic defects in patients with acute promyelocytic leukemia (APL).¹¹⁹ Most, if not all, patients with APL have evidence of DIC at the time of diagnosis. Patients with APL have a higher risk of death during induction therapy as compared with patients with other forms of leukemia, with death most often due to bleeding. Once in remission, APL patients have a higher cure rate than most patients with leukemia. APL is also unique among leukemias in that biologic therapy with retinoic acid or arsenic is effective in inducing remission and cure in most patients. Although effective therapy is available, early death rates due to bleeding have not changed.¹¹⁹

APL patients can present with pancytopenia due to leukemic marrow replacement or with diffuse bleeding due to DIC and thrombocytopenia. Life-threatening bleeding such as intracranial hemorrhage may occur at any time until the leukemia is put into remission. The etiology of the hemostatic defects in APL is complex and is thought to be the result of DIC, fibrinolysis, and the release of prothrombotic extracellular chromatin and other procoagulant enzymes.^119,120 The diagnosis of APL can be straightforward when the leukemic cells are promyelocytes with abundant Auer rods, although some patients have the microgranular form without obvious Auer rods. The precise diagnosis requires molecular methods, including obtaining FISH for detecting the t(15;17) in PML/RARA fusion. Upon diagnosis of APL, one should obtain a complete coagulation profile, including INR, aPTT, fibrinogen, platelet count, and D-dimers. Change in fibrinogen levels tends to be a good marker of progress in treating the coagulation defects.

Therapy of APL involves treating both the leukemia and the coagulopathy. Currently, the standard treatment for APL is trans-retinoic acid (ATRA) in combination with chemotherapy or arsenic.^121,122 This approach will induce remission in more than 90% of patients, and a sizable majority of these patients will be cured of their APL. ATRA therapy will also lead to early correction of the coagulation defects, often within the first week of therapy.¹²³ This is in stark contrast to the chemotherapy era when the coagulation defects would become worse with therapy. Given the marked beneficial effect of ATRA on the coagulopathy of APL and its low toxicity profile, it should be empirically started for any patients suspected of having APL while genetic testing is being performed. Rare reports of massive thrombosis complicating therapy with ATRA exist, but the relationship to either the APL or ATRA is unknown.

Therapy for the coagulation defects consists of aggressive transfusion therapy support and possible use of other pharmacologic agents to control DIC.^124,125 The fibrinogen level should be maintained at over 150 mg/dL and the platelet count at over 50,000 cells/µL.¹²⁶ Controversy still exists over the role of heparin in therapy of APL.¹⁰⁴ Although attractive for its ability to quench thrombin, heparin use can lead to profound bleeding and its use in treating APL has fallen out of favor.

SNAKEBITES

Snake envenomation can lead to direct activation of multiple coagulation enzymes, including factors V, X, thrombin, and protein C, and lead to cleavage of fibrinogen.^127,128 Envenomation can also activate coagulation and damage vascular endothelium. The DIC can be enhanced by widespread tissue necrosis and hypotension. The key to management of snake bites is administration of specific antivenom. The role of prophylactic factor replacement is controversial, but this therapy is indicated if there is clinical bleeding.¹²⁹ One confounder is that some snake venoms, especially rattlesnake, can induce reversible platelet aggregation, which corrects with antivenom.

LOCAL VASCULAR ABNORMALITIES

Abnormal vascular structures, such as vascular tumors, vascular malformations, and aneurysms, can lead to localized areas of thrombin generation that can “spill-over” into the general circulation, leading to DIC. The diagnosis Kasabach-Merritt phenomenon should be reserved for children with vascular tumors such as angioma or hemangioendothelioma.¹³⁰ Therapy depends on the lesion. Embolization to reduce blood flow of vascular malformations can either be definitive therapy or stabilize the patient for surgery. Aneurysms can be repaired by surgery or stenting. Rare patients with aneurysms with significant coagulopathy may require heparin to raise the fibrinogen level before surgery. Kasabach-Merritt disease can respond to steroids or therapy such as vincristine or interferon.¹³⁰ Increasing data shows that use of the mTOR inhibitor sirolimus can shrink these vascular abnormalities leading to lessening of the coagulopathy.¹³¹

CONCLUSION

At the most basic level, DIC is the excess activity of thrombin. However, the clinical presentation and therapy can differ greatly depending on the primary cause. Both diagnosis and therapy involve close coordination of laboratory data and clinical assessment.

Disseminated Intravascular Coagulation

CONCLUSION