DIC Syndrome Calculator – ISTH Overt DIC Score
Calculate the ISTH overt DIC score from platelet count, D-dimer, prothrombin time, and fibrinogen to assess disseminated intravascular coagulation severity.
Enter the patient's coagulation laboratory values to compute the International Society on Thrombosis and Haemostasis (ISTH) DIC score and interpretation.
DIC Syndrome Calculator – ISTH Overt DIC Score
Calculate the ISTH overt DIC score from platelet count, D-dimer, prothrombin time, and fibrinogen to assess disseminated intravascular coagulation severity.
About the DIC syndrome calculator
Disseminated intravascular coagulation (DIC) is a complex, acquired coagulopathy that arises as a secondary complication of diverse and serious underlying conditions. The fundamental pathophysiology involves inappropriate, widespread activation of the coagulation cascade — driven by tissue factor exposure from damaged endothelium, monocyte activation, or direct thrombin generation — leading to simultaneous microvascular thrombosis and consumption of platelets, fibrinogen, and coagulation factors. As clotting factors are depleted and secondary fibrinolysis is activated, the patient paradoxically develops a bleeding tendency despite ongoing intravascular clotting.
The DIC syndrome calculator applies the International Society on Thrombosis and Haemostasis (ISTH) overt DIC scoring algorithm, the most widely validated and internationally accepted tool for diagnosing overt DIC in clinical practice. The ISTH score was developed and validated in large prospective cohort studies demonstrating sensitivity of approximately 93% and specificity of 98% for overt DIC when the score reaches 5 or above.
The scoring system evaluates four coagulation parameters. Platelet count reflects consumption thrombocytopenia: counts between 50 and 100 × 10³/μL score 1 point; counts below 50 score 2. D-dimer — a fibrin degradation product — reflects both fibrin formation and fibrinolysis: moderate elevation (< 5 μg/mL in this implementation) scores 2 points; strong elevation (≥ 5 μg/mL) scores 3. Prothrombin time prolongation from the normal baseline reflects factor VII, X, V, II, and fibrinogen consumption: 3–6 seconds above normal scores 1; more than 6 seconds scores 2. Fibrinogen concentration reflects the net balance between consumption and synthesis: a level at or below 100 mg/dL (1 g/L) scores 1 additional point.
A total score of 5 or above is defined as overt DIC by the ISTH. A score below 5 indicates non-overt DIC — this category encompasses early DIC in a compensated phase where the liver and bone marrow are still meeting the demand for coagulation factor and platelet production. Non-overt DIC requires close monitoring and repeat testing every 24–48 hours, particularly if the clinical condition is deteriorating.
DIC is never a primary diagnosis. The most common triggers include sepsis (accounting for 30–50% of all DIC cases), severe trauma with massive tissue injury, obstetric complications (placental abruption, amniotic fluid embolism, eclampsia), acute leukaemia (particularly the M3 subtype, acute promyelocytic leukaemia, which releases tissue factor from granules), solid organ malignancies, severe burns, and anaphylaxis. Treatment is fundamentally directed at eliminating the underlying trigger. Haemostatic support — fresh frozen plasma for clotting factor replacement, cryoprecipitate for fibrinogen, platelet transfusions in bleeding patients — addresses the consumptive component but does not cure DIC without addressing the cause.
This calculator is intended as a rapid bedside computational aid. The ISTH score should always be interpreted alongside the complete clinical picture, including the patient's bleeding or thrombotic manifestations, the suspected or confirmed trigger, and the trajectory of serial laboratory values rather than a single time point.
DIC calculator examples
Four clinical scenarios from normal coagulation to severe overt DIC.
| Lab Values | ISTH Score | Interpretation |
|---|---|---|
| Platelets 250 ×10³/μL, Fibrinogen 300 mg/dL, PT 12 sec, D-dimer 0.3 μg/mL | Score 0 — No DIC | All values within normal range. No evidence of DIC. |
| Platelets 120 ×10³/μL, Fibrinogen 180 mg/dL, PT 14.5 sec, D-dimer 2.5 μg/mL | Score 2 — Non-Overt DIC | Moderate D-dimer elevation. Platelets borderline low. Monitor and retest. |
| Platelets 80 ×10³/μL, Fibrinogen 120 mg/dL, PT 18 sec, D-dimer 8 μg/mL | Score 5 — Overt DIC | Thrombocytopenia (1 pt), 6 sec PT prolongation (1 pt), markedly elevated D-dimer (3 pts). Total 5: overt DIC confirmed. |
| Platelets 45 ×10³/μL, Fibrinogen 80 mg/dL, PT 25 sec, D-dimer 15 μg/mL | Score 8 — Severe Overt DIC | Severe thrombocytopenia, very low fibrinogen, grossly prolonged PT, massive D-dimer elevation. |
How to use the DIC syndrome calculator
- Enter the platelet count in ×10³/μL (thousands per microlitre) from the most recent CBC.
- Enter fibrinogen in mg/dL, prothrombin time in seconds, and D-dimer in μg/mL from the same blood draw.
- Click 'Calculate ISTH Score' to see the total DIC score and the individual point contributions from each parameter.
- Interpret the total score: ≥ 5 points is compatible with overt DIC and warrants immediate clinical action; < 5 suggests non-overt or early DIC.
- Repeat the scoring daily or every 6–12 hours in critically ill patients, as DIC is a dynamic process that evolves rapidly with the underlying trigger.
DIC syndrome calculator FAQ
What is disseminated intravascular coagulation (DIC)?
Disseminated intravascular coagulation is an acquired syndrome characterised by systemic activation of coagulation leading to fibrin deposition in the microvasculature, consumption of platelets and clotting factors, and secondary fibrinolysis. It is never a primary diagnosis — it always occurs as a complication of a triggering condition such as sepsis, trauma, obstetric complications, malignancy, or severe burns. The simultaneous thrombosis and haemorrhage it produces make it one of the most clinically challenging coagulation emergencies.
How does the ISTH scoring system work?
The International Society on Thrombosis and Haemostasis overt DIC score assigns points to four laboratory markers that reflect different aspects of the coagulopathy. Platelet count below 100 × 10³/μL scores 1 point; below 50 scores 2. D-dimer moderately elevated (< 5 μg/mL) scores 2 points; strongly elevated (≥ 5 μg/mL) scores 3. Prothrombin time prolonged 3–6 seconds above normal scores 1; > 6 seconds scores 2. Fibrinogen ≤ 100 mg/dL (≤ 1 g/L) scores 1 point. A total score ≥ 5 is compatible with overt DIC.
What PT prolongation baseline does this calculator use?
The calculator uses a normal PT baseline of 12 seconds, which is typical for most laboratory reference ranges using standard thromboplastin reagents. If your laboratory's normal range differs, interpret the PT score component accordingly. A PT of 14 seconds would represent 2 seconds of prolongation (scoring 0); 15–18 seconds represents 3–6 seconds (scoring 1 point); above 18 seconds represents more than 6 seconds of prolongation (scoring 2 points).
Can DIC occur with a score below 5?
Yes — a score below 5 indicates 'non-overt' DIC, which represents an early or compensated state where clotting activation has begun but the full haemostatic derangement is not yet manifest in the laboratory. Non-overt DIC can rapidly progress to overt DIC if the underlying trigger is not treated. The ISTH recommends serial repeat testing every 24 hours when clinical suspicion for DIC is present but the initial score is below 5.
What conditions commonly trigger DIC?
The most frequent triggers include sepsis (particularly gram-negative bacteraemia), severe trauma with tissue injury, obstetric emergencies (placental abruption, amniotic fluid embolism, postpartum haemorrhage), acute leukaemia (particularly acute promyelocytic leukaemia), burns, and transfusion reactions. Treating the underlying cause is the primary intervention — supportive coagulation factor replacement with fresh frozen plasma, cryoprecipitate, and platelet transfusions addresses the haematological derangement.
How is DIC treated?
DIC management centres on eliminating the triggering cause while providing haemostatic support. Fresh frozen plasma replaces consumed clotting factors; cryoprecipitate provides fibrinogen and factor VIII; platelet transfusions are considered when counts fall below 50 × 10³/μL in an actively bleeding patient. Anticoagulants such as heparin may be considered in predominantly thrombotic DIC (e.g., Trousseau syndrome in malignancy) but are generally avoided in bleeding-predominant DIC. Outcomes depend on the speed of identification and treatment of the underlying cause.