Diagnostic Tests to Confirm Disseminated Intravascular Coagulation (DIC)
The diagnosis of DIC requires a combination of laboratory tests including platelet count, prothrombin time (PT), fibrinogen, and D-dimer or fibrin degradation products (FDP), with the ISTH scoring system being the gold standard for confirmation. 1
ISTH Diagnostic Scoring System for DIC
The International Society on Thrombosis and Haemostasis (ISTH) recommends using a standardized scoring system that includes:
| Parameter | Score | Range |
|---|---|---|
| Platelet count (×10⁹/L) | 2 | <50 |
| 1 | ≥50, <100 | |
| FDP/D-dimer | 3 | Strong increase |
| 2 | Moderate increase | |
| Prothrombin time (PT ratio) | 2 | >6 seconds (>1.4) |
| 1 | ≥3 seconds, <6 seconds (>1.2, ≤1.4) | |
| Fibrinogen (g/L) | 1 | <100 (<1.0 g/L) |
| Total score for DIC | ≥5 | Overt DIC |
A score of ≥5 confirms overt DIC. 1
Most Efficient Testing Strategy
Initial Testing Panel:
- D-dimer and FDP combination (95% diagnostic efficiency) 2
- Complete blood count with platelet count
- PT/INR
- Fibrinogen level
Additional Tests to Consider:
- Antithrombin level (provides insight into severity and prognosis) 2
- Peripheral blood smear for schistocytes
- Thrombin time
Interpretation of Test Results
- Platelet count: Typically decreased (<150 × 10⁹/L), with severe thrombocytopenia (<50 × 10⁹/L) strongly suggesting DIC 3
- PT/INR: Prolonged (>14 seconds/INR >1.1) 3
- Fibrinogen: Decreased (<1.5 g/L), though may be normal in early stages 3
- D-dimer: Elevated (>0.5 mg/L), with strong elevation highly suggestive of DIC 3
- FDP: Elevated, with 100% sensitivity but lower specificity (67%) 2
Important Clinical Considerations
Serial testing is essential: DIC is a dynamic process, and laboratory values change rapidly. Single measurements may miss the diagnosis. 4
Underlying condition: Always identify the triggering condition (sepsis, trauma, malignancy, obstetric complications) as this is necessary for both diagnosis and treatment. 1
Differentiate from other coagulopathies: Particularly liver disease, which can present with similar laboratory abnormalities but different pathophysiology. 1
Common Pitfalls to Avoid
Relying on a single test: No single test can confirm or rule out DIC; a combination approach is required. 5
Failure to repeat testing: Serial measurements are crucial to monitor the dynamic nature of DIC. 4
Misinterpreting normal fibrinogen: Fibrinogen is an acute phase reactant and may be normal or elevated in early DIC despite ongoing consumption. 3
Overlooking clinical context: Laboratory results must always be interpreted in the context of the patient's clinical presentation and underlying condition. 1
Normal PT/aPTT does not exclude DIC: Especially in subclinical or early forms. 3
Special Situations
Sepsis-induced coagulopathy (SIC): A precursor to DIC in septic patients, diagnosed with a modified scoring system that includes SOFA score and excludes fibrinogen. 1
Liver disease with DIC: Can be challenging to differentiate as both conditions present with similar coagulation abnormalities. Serial testing showing worsening parameters despite stable liver function suggests DIC. 1
By using this systematic approach to laboratory testing and interpretation, DIC can be diagnosed accurately and promptly, allowing for timely intervention to address the underlying cause and manage coagulation abnormalities.