DIC is an acquired hemorrhagic syndrome characterized by uncontrolled formation and deposition of fibrin thrombi. Continuous generation of thrombin causes depletion (consumption) of the coagulation factors and results in uncontrolled bleeding. Also, fibrinolysis is activated in DIC. This further adds to the hemostasis defect caused by the consumption of clotting factors. The many coagulation test abnormalities found in acute DIC include the following:
Prolonged
PT
PTT or activated partial thromboplastin time (aPTT)
Bleeding time
Thrombin time (TT)
Decreased
Fibrinogen
Platelet count
Clotting factors II, V, VIII, and X
Antithrombin III (AT III)
Increased
Fibrinolysin test
Fibrinopeptide A
Positive
Fibrin degradation products (FDPs), also known as fibrin split products (FSPs)
D-dimer
With chronic DIC, the results are variable, especially the PT, PTT, TT, and fibrinogen, making the diagnosis much more difficult. No single test or group of tests is diagnostic, and diagnosis usually depends on a combination of findings. Normal levels do not rule out DIC, and a repeat profile should be done a few hours later to look for changes in platelet count and fibrinogen.
Causes of DIC include septicemia, malignancies and cancer, obstetric emergencies, cirrhosis of the liver, sickle cell disease, trauma or crushing injuries, malaria, incompatible blood transfusion, cold hemoglobinuria or PNH, connective tissue diseases, snake bites, and brown recluse spider bites.
Paradoxically, the treatment of uncontrolled bleeding in DIC is heparin administration. The heparin blocks thrombin formation, which blocks consumption of the other clotting factors and allows hemostasis to occur.
Usually, a blood sample of at least 20 mL is obtained by the two-tube technique. In the first tube, a 5-mL blood sample is obtained and discarded. Then, 15–20 mL of blood is drawn into Vacutainer tubes with sodium citrate as the anticoagulant. A butterfly needle may be used to prevent backflow or to make sampling easier in the case of a difficult draw. Coagulation studies (coagulation profiles, coag panels, coagulograms) are used for screening or as diagnostic tools for evaluation of symptoms such as easy or spontaneous bruising, petechiae, prolonged bleeding (e.g., from cuts), abnormal nosebleeds, heavy menstrual flow, family history of coagulopathies, or gastrointestinal bleeding (Table 2.9).
Many of the more common screening tests are automated and easily done. Platelet counts are included in the automated CBC. PT and PTT can be done on photo-optical instruments that sense the change in optical density when a clot forms. Tests for fibrinogen are on instruments that detect fibrin strands. Many patients can undergo testing at the same time with the help of automation. Some of the more specialized tests still must be done manually or using semiautomated methods.
These five primary screening tests are initially performed to diagnose suspected coagulation disorders:
Platelet count, size, and shape
Bleeding time—reflects data about the ability of platelets to function normally and the ability of the capillaries to constrict their walls
PTT—determines the overall ability of the blood to clot
PT—measures the function of second-stage clotting factors
Fibrinogen level
Factor assays are definitive coagulation studies of a specific clotting factor (e.g., factor VIII for hemophilia). These are done if the screening test indicates a problem with a specific factor or factors.
Fibrinolysis is used to address problems of the fibrinolytic system and includes the following studies:
Euglobulin clot lysis—identifies increased plasminogen activator activity. (Plasmin is not usually present in the blood plasma.)
Factor XIII (fibrin-stabilizing factor)
FDPs (e.g., protamine sulfate test)
The investigation of hypercoagulable status (thrombotic tendency, thromboembolic disorders) covers both primary causes (deficiencies of AT III, protein C, protein S, and factor XII; fibrinolytic mechanisms) and secondary causes (acquired platelet disorders and acquired diseases of coagulation and fibrinolytic impairment) and includes the following tests:
PT
PTT
Fibrinogen test
Antiplatelet factors (e.g., prostacyclin)
Anticoagulant factors (e.g., AT III, protein C, protein S, lupus anticoagulant)
Fibrinolysis tests (e.g., FDPs, euglobulin lysis time [ELT], fibrin monomers)
TT
The lupus inhibitor (lupus anticoagulant) is an antibody (against the phospholipid used in the PT and PTT tests) that is responsible for inhibition of the PT, PTT, dilute Russell viper venom time (dRVVT), and kaolin clotting time (kCT). To demonstrate its presence, 1 mL of the patient’s plasma is mixed with 1 mL of normal plasma, and a PTT test of the mixture is done. When an inhibitor of any sort is present, the PTT will not return to normal range. An inhibitor of the lupus type can be shown by correcting the PTT through use of platelets as a phospholipid source or by demonstrating a characteristic pattern in the PTT that results from sequential dilution of the phospholipid reagent. Lupus anticoagulants may be associated with false-positive Venereal Disease Research Laboratory (VDRL) test reports and with another antiphospholipid—the anticardiolipin antibody (beta2-glycoprotein I).
Clinical Alert
SLE (one fifth of patients)
Multiple myeloma
Other autoimmune diseases (RA, Raynaud syndrome)
Miscarriage (associated with presence of anticardiolipin autoantibody) and postpartum complications
Lupus anticoagulant is more often associated with thromboembolism than with bleeding problems
Most lupus anticoagulant antibodies are directed against prothrombin or beta2-glycoprotein I
Clinical Alert
All patients with hemorrhagic or thrombotic tendencies, or undergoing coagulation studies, should be observed closely for possible bleeding emergencies. A comprehensive history and physical examination should be done.
Blood samples for coagulation studies should be drawn last if other blood studies are indicated.
Procedural Alert
When a blood sample is obtained for PT, PTT, and TT, sodium citrate is used as the anticoagulant in the sampling tubes
Examine all skin for bruising.
Record petechiae associated with use of blood pressure cuffs or tourniquets.
Note bleeding from the nose or gums with no apparent cause.
Estimate blood quantity in vomitus, expectorated mucus, urine, stools, and menstrual flow.
Note prolonged bleeding from injection sites.
Watch for symptoms, especially changes in levels of consciousness or neurologic checks that may signal an intracranial bleed.
Determine whether the patient is taking anticoagulants or aspirin.