A review of disseminated intravascular coagulation: presentation, laboratory diagnosis and treatment.

Normal hemostasis is a complex interaction of platelets, blood vessels, and the procoagulant and fibrinolytic proteins. Disseminated intravascular coagulation (DIC) occurs when a stimulus pathologically activates coagulation, subsequently causing that interaction to become unbalanced. Although excess coagulation predominates, it is almost always accompanied by up-regulated compensatory fibrinolysis. DIC is not a specific disease but is the unwanted result of many disease states or precipitating events. Rapid diagnosis of DIC, resolution of the underlying disease or precipitating event, and appropriate therapy are critical for a favorable patient outcome. Many cases of DIC can be diagnosed using tests commonly found in most laboratories, and research indicates that newer tests may make diagnosis of DIC even easier.

To fully understand the complexities of DIC, it is essential to understand what occurs in normal hemostasis, which involves the interaction of primary hemostasis (action of platelets and vessels), secondary hemostasis (formation of the fibrin clot), and fibrinolysis (degradation of the fibrin clot and restoration of normal blood flow). The complexity, and biochemistry of vascular homeostasis is well described in many sources.[1] Normally, a blood vessel's interior is antithrombotic, because vascular proteoglycans inhibit platelet aggregation and control the interaction of coagulant proteins with the vessel wall by accelerating antithrombin (AT) activity.[2]

Nonpathologic coagulation

In a nonpathologic state, when a vessel is injured, several processes help minimize blood loss from the damaged vessel. During primary hemostasis, vasoconstriction begins to divert blood from the injured vessel. Platelets adhere to the exposed endothelial basement membrane and then aggregate to form a platelet plug. During secondary hemostasis, a fibrin clot forms and stabilizes the platelet plug. This fibrin clot forms via (1) the intrinsic coagulation pathway, when activated factor XII (FXIIa) binds to the exposed endothelial cells at the site of injury and (2) the extrinsic coagulation pathway, when small amounts of circulating FVIIa bind to tissue factor released from injured endothelial tissues. The tissue factor-FVIIa complex provides additional activation of a complex (FIXa-FVIIIa) within the intrinsic pathway.

Both coagulation pathways in secondary hemostasis consist of a series of enzymatic reactions that lead to the formation of thrombin, which performs several powerful enzymatic activities. Thrombin cleaves fibrinogen to form fibrin monomers and release fibrinopeptides A and B. These newly formed fibrin monomers weakly bind into a loose fibrin clot. Thrombin also converts factor XIII into a transamidase that forms covalent bonds within the loose clot and stabilizes it. Additionally, thrombin further activates factors V and VIII and platelets, all of which provide positive feedback into the coagulation sequence.

Coagulation inhibitors. Inhibition of these activated coagulation pathways is maintained by (1) tissue factor pathway inhibitor, which prolongs the initiation stage of coagulation (low-level thrombin production); (2) AT, which decreases the rate of thrombin development during the propagation stage (explosive thrombin production)[3]; and (3) the protein C system, which is activated when thrombin binds with thrombomodulin on the vessel. Activating protein C inactivates primarily factor Va, which then inactivates thrombin.

Fibrinolysis. To restore blood flow through the healed vessel, the fibrin clot is lysed by enzymatic reactions much like coagulation. The active protein in this fibrinolytic system is plasmin, which is produced as plasminogen and is activated by (1) kallikrein generated by the intrinsic coagulation pathway, (2) tissue plasminogen activator released from the injured endothelial cells, and (3) urokinase produced by kidney endothelial cells. Plasmin performs multiple enzymatic activities, but most importantly it degrades the fibrin clot or fibrinogen into fibrinogen degradation products (FDPs), including fragments X and Y (early split products) and D and E (late split products). High concentrations of these late FDPs will interfere with fibrin monomer formation and increase vascular permeability and vasodilation.

With one exception, these early and late FDPs are the same, regardless of whether fibrin or fibrinogen is cleaved by plasmin. The exception is the dimer form of fragment D (D-dimer), which is present only after fibrin has been cleaved by plasmin.[4] A D-dimer assay can determine whether fibrin has been degraded, and this can be important information when diagnosing DIC.

Two forms of tissue plasminogen activator inhibitor (TPAI) control plasminogen activation: TPAI-1, which is produced by endothelial cells, platelets, smooth muscle cells, and hepatocytes; and TPAI-2, which is found in placental tissue, granulocytes, and the monocyte-macrophage.[5] Further plasmin inhibition is achieved by the circulating inhibitors [Alpha]2-antiplasmin (a rapid plasmin inhibitor) and [Alpha]2-macroglobulin (a slow plasmin inhibitor).[6] Control of the plasmin concentration is important, because in abnormally high concentrations, plasmin destroys fibrinogen, active forms of factors V and VIII, and other serine proteases.

Additional resolution of blood vessel injury, occurs as a result of clot retraction, the consolidation of the platelet plug by the formation of the fibrin stable clot throughout the platelet plug, and repair of the endothelial cells by platelet-derived growth factor.[1] The balance among all the previously mentioned intricate pathways is essential to prevent blood loss through the injured vessel, repair the injured vessel, and reestablish blood flow through the vessel to achieve vascular homeostasis.

DIC

DIC occurs when the coagulation response to endothelial cell damage is out of balance and becomes a systemic abnormality, producing fibrin that is disseminated throughout the microcirculation, hence the term "disseminated intravascular coagulation" ([ILLUSTRATION FOR FIGURE OMITTED], p. 52). The disseminated microthrombi decrease tissue oxygenation, which causes organ infarction and necrosis and eventual increased release of tissue factor. The latter contributes to continued intravascular fibrin formation and plasmin activation.

The uncontrolled fibrin formation consumes the coagulation factors and platelets, while plasmin continues to degrade formed fibrin clots and circulating fibrinogen. This combination of fibrinolysis and consumption of coagulation factors and platelets produces bleeding. Activation of the kinin system by kallikrein causes increased vascular permeability and vasodilation, and both lead to hypotension and shock. In addition, the patient's liver function is taxed by the need to remove FDPs, activated factors, and immune complexes, as well as by the need to make more coagulation factors.

Acute DIC. Classically, DIC presents with an obvious, precipitating event or disease state and often begins abruptly. If the disease course is hemorrhagic, symptoms often include ecchymoses, epistaxes, petechiae, and bleeding or oozing from needle puncture, surgical, and wound sites. In addition to or sometimes alone, microvasculature obstruction by thrombi causes disseminated microinfarcts that quickly produce shock when the major organs, such as heart, liver, brain, and kidneys, are affected.[7] Both the bleeding and shock can lead to death. Other general observations will be hypoxia, proteinuria, fever, acidosis, and hypotension.

For patients with the classic, acute course of DIC, diagnosis is fairly simple (see Tables 1 and 2). The prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT) will all be prolonged because of the consumption of the coagulation factors - although with the advent of D-dimer, TT is no longer offered as a routine test. Consumption will also decrease results for quantitative fibrinogen and platelet counts. The peripheral blood smear usually contains schistocytes, because erythrocytes are sheared on the fibrin deposits in the vessels. Specific tests for FDPs and D-dimer are both elevated because of increased fibrinolysis.

Many well-documented precipitating events and diseases are associated with increased risk of developing the DIC syndrome (see Table 3).[8] Regardless of the cause, DIC patients present with many of the preceding characteristics, and acute DIC may develop within a few hours to a few days after a precipitating event begins. However, each patient's presentation depends on the intensity and duration of the DIG stimulus - that is, the severity of the patient's precipitating pathology and the body's ability to control this process. The latter depends especially on (1) the functional ability of the liver to replace coagulation factors and remove FDPs and (2) the bone marrow's ability to replace the platelets.

Regardless of the cause, the characteristics of acute DIC are similar in each case; and this overt, acute form is relatively easy to diagnose. The most common category of DIC encountered in the laboratory is the classic presentation previously mentioned. It presents with uncontrolled activation of both coagulation and fibrinolysis, but the decrease in coagulation factors is greater than the increase in lysis, because the liver and bone marrow cannot make coagulation factors or platelets fast enough to compensate for their increased consumption. [TABULAR DATA FOR TABLE 2 OMITTED] Consequently, the patient presents with bleeding that would be diagnosed as being caused by acute, decompensated DIC.

Chronic DIC. Approximately 1020% of DIC patients[7] exhibit another form of the syndrome that is not as easy to diagnose. Chronic, compensated DIC occurs when fibrin clot formation and the accompanying fibrinolysis are in a steady state because the liver and bone marrow can compensate for the increased use of coagulation factors and platelets while still clearing FDPs and circulating activated factors from the peripheral blood. Because of the lack of excess bleeding, this chronic, compensated DIC is much less obvious than acute DIC, and in combination with minimally abnormal laboratory results, this may delay diagnosis and therapy while contributing to an unfavorable patient outcome. Chronic DIC will likely degenerate into an overt form of acute DIC if (1) in its chronic form, the DIC is not diagnosed and treated successfully and (2) the underlying stimulus for the chronic DIC persists or intensifies.[9]

Table 3

Conditions commonly associated with development of DIC

Acute, decompensated           Chronic, compensated

Obstetrical complications      Obstetrical complications
Septicemias                    Collagen/vascular disease
Liver disease                  Cardiovascular disease
Traumatic injuries             Metastatic malignancy
Burns                          Renal diseases (such as hemolytic
                               uremic syndrome)
Acute promyelocytic leukemia   RBC-related hematologic diseases
                               (such as polycythemia vera)
Poisonous snake bite

Coagulation pathways activated. DIC can be triggered by damage to or alteration of endothelial cells, by massive release of tissue factor, or by direct activation from proteolytic enzymes. However, for any given DIC stimulus, more than one activation pathway may be involved (see Table 4).[6,7] When endothelial cells are damaged, the exposed collagen activates FXII, which stimulates the intrinsic pathway and converts prekallikrein to kallikrein to activate fibrinolysis. Some of the most common triggers of DIC that can activate the intrinsic coagulation pathway include sepsis, liver disease, immune complex disease, heat stroke, burns, anoxia, shock, and obstetrical complications such as placental abruption.[8] Of these, sepsis is one of the most common, especially when caused by the release of endotoxins from gram-negative organisms.[10] However, this form of sepsis often activates more than one coagulation pathway.[6] During sepsis, activation of the intrinsic coagulation pathway is accompanied by a decrease in thrombomodulin production and in the function of proteins C and S. Together, these changes minimize the body's ability to inhibit the pathologic coagulation associated with DIC.[11]

Activation of the extrinsic pathway occurs as FVII is activated when massive amounts of tissue factor are released during tissue necrosis and organ failure. Triggering mechanisms may include traumas, obstetrical complications such as fetal demise, tumors that produce a thromboplastin-like substance, and chemotherapy for acute promyelocytic leukemia. The latter destroys the elevated promyelocyte population, causing the promyelocytes to release granules containing procoagulants. This type of trigger may also be seen in patients who have an untoward red blood cell (RBC) lyric event, which may also trigger the extrinsic pathway, as ADP is released from the lysed RBCs or thromboplastic material is released from white cells and platelets and the RBC stroma.[10,12]

Table 4

Coagulation pathways activated by DIC stimuli

Factor XII activation by endothelial cell damage

Acidosis                           Intravascular hemolysis(1)
Anoxia                             Liver disease(1)
Burns                              Sepsis(1)
Heat stroke                        Vasculitis
Immune complex disease

Factor VII activation by release of thromboplastin

Acute intravascular hemolysis(1)   Placental abruption
Amniotic fluid embolus(1)          Promyelocytic leukemia
Cardiopulmonary bypass surgery     Retained dead fetus syndrome(1)
Fat emboli syndrome                Sepsis(1)
Mucin-secreting adenocarcinoma     Trauma

Activation of factors X and/or II

Acute pancreatitis                 Liver disease(1)
Fat emboli syndrome(1)             Snake venoms(1)

1 More than one mechanism may be involved.

Adapted from: Lazarchick J, Kizer J. Interaction of the
fibrinolytic, coagulation, and kinin systems and related pathology.
In: Harmening DM, Ed. Clinical Hematology and Fundamentals of
Hemostasis. 3rd ed. Philadelphia, PA: FA Davis Company; 1997.

Direct activation of factor X or prothrombin can occur in the presence of proteolytic enzymes found in snake venom and in association with liver disease and acute pancreatitis. Direct degradation of the coagulation proteins may also occur as a complication of thrombolytic therapy with urokinase or tissue plasminogen activator.[8]

Treatment

When the underlying disease or precipitating event is known and the diagnosis of DIC is certain, traditional therapy must include resolution of the precipitating event, if possible. For example, in an obstetric patient with fetal demise, the fetus must be removed to limit the extent and scope of DIC.[13] Conversely, DIC caused by other conditions, such as gram-negative sepsis, is more difficult to treat because of the inability to easily and quickly remove the organisms.[11] However, for many septic patients, appropriate antibiotic therapy can minimize pathophysiologic changes caused by DIC.[6]

In addition to receiving treatment for the precipitating event, patients must receive replacement therapy for coagulation factors (fresh frozen plasma or cryoprecipitate) and platelets (platelet concentrate) consumed during excess fibrin formation, as well as erythrocytes lost if substantial hemorrhage occurred. If thrombosis is damaging organ function, and reversing the damage is possible, patients may receive subcutaneous low-dose heparin to limit the uncontrolled clotting process.[5] However, the use of heparin in acute DIC is controversial[14] because it can cause fatal bleeding.[7] Patients with chronic, compensated DIC may also receive heparin to stop the clotting process. If this process is not stopped, tissue oxygenation will continue to decrease, with development of acute DIC and possible subsequent tissue necrosis and multiple organ failure as the final result.

Therapeutic use of heparin changes the conformation of AT so that it becomes up to 1,000 times more able to inactivate the serine proteases. Because AT is the most important thrombin inhibitor,[5] increasing its ability to function may effectively stop the accelerated formation of thrombin. However, if a patient is AT deficient, heparin will not be an effective therapeutic option. Consequently, AT concentrate is being evaluated for its ability to control or reverse DIC.[11] AT concentrate may also be indicated, even when the use of heparin is not an option, because other functions of AT (reduced release of lysosomal proteinases and soluble intercellular adhesion molecules and increased release of prostacyclin, among others) help minimize endothelial damage, which almost always occurs during DIC.[9] In fact, evidence suggests that at least AT's role in increased release of prostacyclin may actually be inhibited by the presence of heparin.[9]

In less obvious cases of chronic, compensated DIC, a timely and reliable diagnosis must be available to allow appropriate therapy for a favorable patient outcome. No test is specific for DIC, and most laboratories provide physicians with results from a DIC panel that may include PT, APTT, fibrinogen, platelet count, FDP, and D-dimer. While these test results should change for acute DIC in ways indicated in Table 1, physiologic factors for each patient may influence the results of some panel tests and mask the presence of chronic DIC. Consequently for these patients, comparing serial results from the panel of hemostatic tests more reliably indicates a consumptive process than a random result.

The PT and APTT results may be normal in the compensated patient, and both tests may be affected by oral anticoagulants (PT) and heparin (APTT) therapy. Therefore, a series of increasingly prolonged results for PT and APTT is a better indicator of uncontrolled consumption of coagulation factors. The reference range for platelets is broad (see Table 2), and many patients who have decreased platelet counts do not have DIC. Consequently, serial evidence of DIC provided by platelets should include progressive thrombocytopenia in addition to abnormal results of the other DIC panel tests. Also, many clinical states, especially pregnancy and infection, produce elevated fibrinogen levels. Decreased fibrinogen is generally observed in patients with acute DIC, but fibrinogen may be normal or even elevated (see Table 1) in patients with chronic, compensated DIC, depending on the initial fibrinogen value. Therefore, demonstration of a progressive decrease in both platelet count and fibrinogen, rather than critically low results, is most helpful when diagnosing chronic, compensated DIC.

FDP and D-dimer techniques

Performance of the FDP by latex agglutination will detect semi-quantitative fragments D and E produced by the breakdown of either the fibrin clot (fibrinolysis) or fibrinogen (fibrinogenolysis). To closely approximate the patient's in vivo status, specimen collection for this test requires a special tube that contains (1) thrombin to ensure clotting and complete removal of fibrinogen from the sample and (2) a proteolytic inhibitor of in vitro fibrinolysis. Latex particles, coated with antibodies to human fibrinogen fragments D and E, are mixed with patient serum (or urine). These latex particles agglutinate when FDP is present, although timing and dilution requirements must be strictly observed. The reference range for FDP is less than 2 [[micro]gram]/mL, with values greater than 10 [[micro]gram]/mL, indicating increased activation of fibrinolysis.[15] The FDP is an extremely sensitive test that measures fibrinolysis and/or fibrinogenolysis with essentially no false negatives. Therefore, a positive FDP will indirectly indicate DIC. However, FDP is not specific for DIC, and false positives are observed after exercise or stress, in patients with liver disease or infection, and during pregnancy.

The D-dimer is a better indicator for DIC than the FDP test because D-dimer detects the factor XIII-cross-linked-D fragments produced by plasmin degradation of the stable fibrin clot (fibrinolysis). Therefore, in addition to the fibrinolytic activity of plasmin, the presence of D-dimer indicates the coagulant activity of thrombin. In one study, the D-dimer had the best predictive value of any test in a DIC panel.[16]

The D-dimer latex agglutination test is less sensitive than the one for FDP but is highly specific for the D-D fragment produced by plasmin degradation of fibrin. This test provides rapid results and is used frequently. It requires no special tube and uses latex particles coated with monoclonal antibodies to the D-D fragment of FDP. These particles agglutinate when mixed with plasma containing D-dimer. Normal values are less than 0.5 [[micro]gram]/mL, and a positive D-dimer (values greater than 1.0 [[micro]gram]/mL) can be seen in patients with DIC,[17] deep venous thrombosis, pulmonary embolism, neoplasia, liver disease, and inflammatory disorders, as well as after surgery.[16,18]

Three other methods for detecting D-dimer include immunoblotting, enzyme-linked immunosorbent assay (ELISA), and the Liatest D-dimer (Diagnostica Stago, Asnieres, France).[16,19,20] Immunoblotting is as sensitive as the FDP and highly specific for D-dimer, detecting it at lower levels than latex agglutination. However, immunoblotting is time consuming, and this requirement markedly decreases its clinical utility. The ELISA test is more sensitive than latex agglutination and less time consuming than immunoblotting. However, D-dimer ELISA is generally performed as a batch test that requires several hours to complete.

The Liatest D-dimer, an automated microlatex assay, has been studied as a means to exclude pulmonary embolism.[20] Advantages of the Liatest are a sensitivity comparable to ELISA procedures with a much shorter performance time (10 minutes) and increased reproducibility compared to the latex agglutination procedure[19] because the Liatest is read on an automated coagulation instrument. Future research evaluating the use of Liatest D-dimer in additional clinical settings may indicate its use as a quick, reliable assay to detect elevated D-dimer DIC patients.

Although results from many tests are used to diagnose DIC, the FDP and D-dimer tests provide one of the best combinations to monitor the patient at risk for this condition. The FDP has excellent sensitivity, and the D-dimer assay is a great confirmatory test because of its high predictive value.[16] For the most favorable patient outcome, the laboratory must be able to monitor development of intravascular thrombi. This permits appropriate treatment to prevent tissue ischemia, necrosis, and organ failure.

Although not generally included in a routine DIC panel, a functional AT assay can be an important means to evaluate the efficacy of DIC therapy as well as a predictor of DIC outcome. This is true especially in DIC caused by sepsis

because the precipitating cause cannot be readily removed and early detection of DIC increases the possibility of a favorable patient outcome.[11] As a physiologic inhibitor of thrombin activity, AT activity levels decrease because of increased consumption of AT when thrombin activation increases during DIC. When AT levels decrease, additional thrombosis can occur as a result of decreased control of thrombogenic activity. Functional AT levels can best be determined by chromogenic substrate,[21] and normal activity is generally 85-115%.[22] By offering functional AT activity levels, the clinical laboratory may enhance diagnosis of chronic, compensated DIC.[11] Research is currently being conducted to evaluate the possible use of both TAT complexes and Fl.2 assays to diagnose both forms of DIC more accurately, easily, and rapidly.

Differential diagnosis: DIC versus primary fibrinolysis

Primary fibrinolysis is a rare disorder with a clinical presentation similar to acute DIC.[9] Primary fibrinolysis when plasminogen is activated to plasmin without the prior coagulant action of thrombin. This circulating plasmin can then degrade fibrinogen and factors V and VIII before they can be used in the normal clotting process. During primary fibrinolysis, plasminogen can be activated directly by proteolytic enzymes resulting from urologic disease (release of urokinases), metastatic carcinoma, decreased liver clearance of plasminogen activators, or decreased physiologic inhibitors of plasmin ([Alpha]2-antiplasmin and [Alpha]2-macroglobulin).[6]

Antifibrinolytic drugs, such as aprotinin, [Xi]-aminocaproic acid, tranexamic add, or natural antiplasmins, are usually used to treat primary fibrinolysis. However, diagnosis must be definite before treatment begins because results for many hemostatic tests will be the same in primary fibrinolysis and in acute DIC (see Table 1). The PT and APTT will be prolonged; fibrinogen will be decreased, and FDP will be increased. However, since platelets are not being consumed in primary fibrinolysis, the PLT count will remain above 100,000/[mm.sub.3].[14] Also, because thrombin is not being activated, D-dimer will be normal.[6]

In the past, paracoagulation tests have been used to help differentiate DIC from the rare occurrence of primary fibrinolysis. The protamine sulfate gelation test detects the presence of the fibrin monomer produced by thrombin activity on fibrinogen. Protamine sulfate is added to plasma, and, if fibrin monomers are present, a loose clot will form suggesting DIC. Without the presence of thrombin, no fibrin monomers are present, and no clot will form. When the proper combination of abnormal laboratory results and patient symptoms exists, a negative protamine sulfate test suggests primary fibrinolysis.[8] The ethanol gelation test is very similar to the protamine sulfate gelation test and also detects fibrin monomer that forms after thrombin generation. However, neither test is specific or sensitive,[7] and both have been largely replaced by other tests, such as D-dimer, to indicate whether coagulation has been activated.

In summary, diagnosis of overt, acute, decompensated DIC is often straightforward. A precipitating event (obstetrical complication) or predisposing disease (acute promyelocytic leukemia) will precede clinical evidence of the DIC process (bleeding, petechiae, hypotension, and shock). The laboratory values (prolonged PT and APTT, decreased PLT and fibrinogen, and increased FDP and D-dimer) demonstrate a consumptive coagulopathy with increased degradation of fibrin/fibrinogen. Successful treatment must always include resolution of the triggering mechanism as soon as possible and restoration of depleted coagulation factors and platelets. If appropriate, heparin or AT concentrate may be used to control thrombotic activity.

Patients at risk for chronic, compensated DIC are a diagnostic challenge. Clinical evidence of DIC in these patients may not be observed until acute DIC develops, perhaps with end-stage organ failure. Also, laboratory tests from the DIC panel may not be as informative during chronic DIC, especially if only one set of results is provided instead of a series. Patients whose clinical status places them at risk for chronic, compensated DIC require (1) more aggressive monitoring of clinical status, (2) serial laboratory testing, and (3) inclusion of nontraditional coagulation tests, such as AT levels. By more accurately providing a diagnosis in the early stages of DIC, more aggressive therapy (subcutaneous heparin and/or AT concentrate) may be given sooner and provide more favorable patient outcomes.

CONTINUING EDUCATION

To earn CEUs, see test on page 56.

LEARNING OBJECTIVES:

1. Describe the mechanisms of normal circulatory hemostasis.

2. Describe the disease states commonly associated with development of DIC.

3. Identify laboratory tests for diagnosis of DIC.

CE test published through an educational grant from

References

1. Harmening DM, Lemery LD. Introduction to hemostasis In: Harmening D, ed. Clinical Hematology and Fundamentals of Hemostasis. 3rd ed. Philadelphia, PA: F. A. Davis Company; 1997: p. 481-508.

2. Lotspeich-Steininger CA. Introduction to Hemostasis. In: Stiene-Martin EA, Lotspeich-Steininger CA, Koepke JA, eds. Clinical Hematology Principles, Procedures, Correlations. 2nd ed. Philadelphia, PA: Lippincott-Raven Publishers; 1998: p. 599-611.

3. Mann KG, van't Veer C, Cawthern K, Butenas S. The role of the tissue factor pathway in initiation of coagulation. Blood Coagulation and Fibrinolysis. 1998;9(suppl 1):S3-7.

4. Jobe MI. Mechanisms of coagulation and fibrinolysis. Introduction to hemostasis. In: Stiene-Martin EA, Lotspeich-Steininger CA, Koepke JA, eds. Clinical hematology principles, procedures, correlations. 2nd ed. Philadelphia, PA: Lippincott-Raven Publishers; 1998: p. 612-634.

5. Canton MM. Introduction to thrombosis and anticoagulant therapy. In: Harmening D, ed. Clinical Hematology and Fundamentals of Hemostasis. 3rd ed. Philadelphia, PA: F. A. Davis Company; 1997: p. 566-585.

6. Lazarchik J, Kizer J. Interaction of the fibrinolytic, coagulation, and kinin systems and related pathology. In: Harmening D, ed. Clinical Hematology and Fundamentals of Hemostasis. 3rd ed. Philadelphia: F. A. Davis Company; 1997: p. 554-565.

7. McKenzie SB. Disorders of secondary hemostasis. In: Textbook of Hematology. Baltimore, MD: Williams and Wilkins; 1996; 561-600.

8. Bick RL. Disorders of Thrombosis & Hemostasis Clinical Laboratory Practice. Chicago: ASCP Press; 1992.

9. Balk R, Emerson T, Fourrier F, Kruse JA, Mammen EF, Schuster H-P, Vinazzer H. Therapeutic use of antithrombin concentrate in sepsis. Seminars in thrombosis and hemostasis. 1998;24(2): 183-194.

10. Jensen R. Disseminated intravascular coagulation. Clinical Hemostasis Review. 1996; 10(5): 1-4.

11. Mammen EF. Case of the month, disseminated intravascular coagulation (DIC) and sepsis. Clinical Hemostasis Review. 1996; 10(5): 18.

12. Vengelen-Tyler V. Technical Manual. 12th ed. Bethesda, MD: American Association of Blood Banks; 1996: p. 545.

13. Jensen R. Hemostasis and the obstetric patient. Clinical Hemostasis Review. 1996; 10(1): 1-4.

14. Schmidt MC. Hemorrhagic disorders of coagulation and fibrinolysis. In: Stiene-Martin EA, Lotspeich-Steininger CA, Koepke JA, eds. Clinical Hematology Principles, Procedures, Correlations. 2nd ed. Philadelphia, PA: Lippincott-Raven Publishers; 1998: p. 661-681.

15. Thrombo-Wellcotest* [package insert]. Murex Diagnostics Limited. Central Road, Temple Hill, Dartford, England DAI 5LR. July 1995.

16. Carr JM, McKinney M, McDonagh J. Diagnosis of disseminated intravascular coagulation, role of D-dimer. Am J Clin Path. 1989; 91(3):280-287.

17. D-dimer Wellcotest* [package insert]. Murex Diagnostics Limited. Central Road, Temple Hill, Dartford, England DAI 5LR. June 1992.

18. Greenberg CS. The DIC syndrome: A clinical and laboratory challenge. Clinical Hemostasis Review. 1996; 10(5): 13-14.

19. Reber G, Bounameaux H, Perrier A, de Moerloose P. Performances of a new, rapid and automated microlatex D-dimer assay for the exclusion of pulmonary embolism in symptomatic outpatients. Thrombosis and Haemostasis. 1998;80(4):719-20.

20. Oger E, Leroyer C., Bressollette L. et al. Evaluation of a new, rapid, and quantitative D-dimer test in patients with suspected pulmonary embolism. Am J Respir Crit Care Med. 1999;158:65-70.

21. Ens GE, Wyrick-Glatzel J. Coagulation. In: Harmening D, ed. Clinical Hematology and Fundamentals of Hemostasis. 3rd ed. Philadelphia. PA: F. A. Davis Company; 1997: p. 657-681.

22. Tietz NW. Clinical Guide to Laboratory Tests. 3rd ed. Philadelphia, PA: W.B. Saunders Company; 1995: p. 64.

Vickie L. Cunningham is MLT-C Program Director, Bluefield Regional Medical Center, Bluefield, WV.