What laboratory tests are typically abnormal in Disseminated Intravascular Coagulation (DIC)?

Laboratory Abnormalities in Disseminated Intravascular Coagulation (DIC)

In DIC, the core laboratory abnormalities include decreased platelet count, decreased coagulation factors (prolonged PT/PTT), decreased fibrinogen, and elevated D-dimer levels, reflecting the consumptive coagulopathy and ongoing fibrinolysis that characterize this syndrome. 1

Core Laboratory Tests and Expected Abnormalities

Platelet Count

• Thrombocytopenia is a hallmark finding, with platelets typically moderately to markedly reduced 1
• A 30% or higher drop in platelet count should be considered diagnostic of subclinical DIC even when absolute values remain in the normal range 1, 2
• The decreasing trend is more important than absolute values, particularly in patients with initially elevated counts who may still have "normal" platelet counts despite significant consumption 1, 2

Coagulation Profile

• Prothrombin Time (PT) and Partial Thromboplastin Time (PTT) are typically prolonged due to consumption of coagulation factors 1
• Important caveat: PT and PTT may not be prolonged in approximately 50% of cases, especially in subclinical or early cancer-associated DIC when coagulation factors are only moderately decreased 1
• Diagnosis should be made by finding abnormalities in at least 3 of 4 laboratory values (PT, platelet count, fibrinogen, and fibrin degradation products) 3

Fibrinogen

• Decreased fibrinogen levels occur due to consumption, though levels may still be within normal range in some cases 1, 2
• Severe hypofibrinogenemia is defined as <1 g/L 4

Fibrin Degradation Products

• Elevated D-dimer is highly sensitive for DIC diagnosis and indicates active fibrinolysis 2, 5
• Fibrin/fibrinogen degradation products (FDP) are elevated 1
• The D-dimer and FDP combination has the highest diagnostic efficiency of 95%, with sensitivity of 91% and specificity of 94% 5
• FDP alone has 100% sensitivity but only 67% specificity 5

Additional Confirmatory Tests

Factor VIII and von Willebrand Factor

• Low and/or declining levels of Factor VIII and VWF serve as confirmatory tests of consumptive coagulopathy 1, 2
• These should not be decreased in adaptive changes of liver disease, making them useful to distinguish DIC from cirrhotic coagulopathy 1

Antithrombin (AT)

• Declining AT levels suggest consumptive coagulopathy 1, 2
• Particularly useful in clinical management of patients with renal failure who paradoxically clot dialysis filters despite profound coagulopathy 1

Critical Monitoring Principles

Dynamic Nature of DIC

• Rapid changes in laboratory values (hours to days) are sine qua non for DIC 1
• Serial testing is essential as DIC is a dynamically changing scenario 4
• Monitoring frequency should range from monthly to daily depending on clinical circumstances 2

Trend Monitoring Over Absolute Values

• A decreasing trend in platelets should be considered a marker of continuing thrombin generation even when absolute counts remain normal 1
• This is particularly important in patients with hematological malignancies where marrow failure and chemotherapy independently affect platelet counts 1

Common Pitfalls in Laboratory Interpretation

Normal Values Don't Exclude DIC

• Normal coagulation screen does not rule out DIC, as this was only noted in about 50% of septic DIC cases 1
• Normal platelet count despite a significant drop from baseline can be misleading and may be the only sign of DIC in some patients with malignancy 1, 2

Distinguishing DIC from Liver Disease

• Liver disease can cause similar laboratory abnormalities but typically doesn't show the rapid changes characteristic of DIC 1, 2
• In cirrhosis, changes in hemostatic parameters usually do not change rapidly, whereas in DIC rapid changes are essential for diagnosis 1
• Factor VIII and VWF levels help distinguish: these are low in DIC but normal or elevated in liver disease 1, 2

Recommended Laboratory Panel

Initial Diagnostic Panel

• Complete blood count (CBC) with platelet count 2
• PT and PTT 2, 4
• Fibrinogen level 2, 4
• D-dimer and/or FDP 2, 5

Confirmatory Tests When Diagnosis Uncertain

• Factor VIII 1, 2
• von Willebrand Factor 1, 2
• Antithrombin 1, 2

Optimal Rapid Diagnostic Combination

• D-dimer, FDP, and antithrombin provide the best diagnostic panel, with D-dimer and FDP providing rapid and specific diagnosis, and antithrombin providing insight into severity and prognosis 5