DIC Syndrome Calculator - ISTH Scoring System
This calculator applies the International Society of Thrombosis and Haemostasis (ISTH) scoring algorithm to assess the likelihood of overt disseminated intravascular coagulation (DIC). Enter the four laboratory parameters below, and the calculator returns a score from 0 to 8, the corresponding clinical interpretation, and a step-by-step breakdown of how each parameter contributed. A score of 5 or above is compatible with overt DIC at 93% sensitivity and 98% specificity.
Formula
Worked example
A patient with sepsis has: platelet count 60 x 10⁹/L (1 point), D-dimer strongly elevated > 7x ULN (3 points), PT prolonged 4 seconds above ULN (1 point), fibrinogen 1.2 g/L (0 points). Total = 1 + 3 + 1 + 0 = 5 points, compatible with overt DIC.
What is disseminated intravascular coagulation (DIC)?
Disseminated intravascular coagulation (DIC) is an acquired, life-threatening disorder in which systemic activation of the coagulation cascade leads to widespread formation of microthrombi throughout the vasculature. As clotting factors and platelets are consumed faster than they can be replaced, the same process that causes excessive clotting also paradoxically leads to bleeding from sites that would normally clot normally. The 2025 ISTH definition characterizes DIC as "an acquired, life-threatening intravascular disorder characterized by systemic coagulation activation, dysregulated fibrinolysis, and endothelial injury, resulting in microthrombosis." DIC is always secondary to an underlying condition - it is never a primary diagnosis. Common triggers include severe sepsis, major trauma, solid tumors, hematologic malignancies, obstetric emergencies such as placental abruption, transfusion reactions, and severe burns. Mortality ranges from about 10% in mild cases to more than 50% in sepsis-associated DIC, making prompt recognition critical.
How the ISTH scoring algorithm works
The ISTH overt DIC algorithm was developed as a consensus guideline by the International Society of Thrombosis and Haemostasis to create a reproducible, bedside-applicable diagnostic tool. It evaluates four routine laboratory parameters: platelet count, fibrin-related markers (D-dimer or fibrin degradation products), prothrombin time prolongation, and fibrinogen level. Each parameter is assigned points based on the degree of abnormality, with the total score ranging from 0 to 8. A score of 5 or higher is considered compatible with overt DIC at 93% sensitivity and 98% specificity in the original validation cohort. Scores below 5 do not exclude DIC - they indicate that DIC may be in a pre-overt (non-overt) stage and the score should be repeated in 24-48 hours if clinical suspicion remains. The algorithm should only be applied to patients who already have a recognized underlying condition capable of triggering DIC. It is not a screening tool for unselected populations. For pregnant patients beyond 20 weeks gestation, a modified version omitting D-dimer (which is physiologically elevated in pregnancy) is used.
What each laboratory parameter signals
Platelet count reflects consumptive thrombocytopenia from platelet trapping in microthrombi. The count typically falls progressively over hours to days, so serial trending is as important as any single value. Fibrin-related markers, principally D-dimer and fibrin degradation products (FDPs), reflect the breakdown of cross-linked fibrin and are the most sensitive indicator of active thrombin and plasmin generation. D-dimer is more specific than FDPs when expressed as a multiple of the local upper limit of normal, which is why the 2025 update uses thresholds of more than 3x ULN (moderate) and more than 7x ULN (strong). Prothrombin time prolongation signals consumption or decreased synthesis of vitamin K-dependent clotting factors (factors II, V, VII, X). Significant prolongation (6 seconds or more above the upper limit of normal) usually indicates depletion severe enough to require factor replacement. Fibrinogen is an acute-phase reactant: early in DIC it may actually rise due to the inflammatory response, so a level below 1 g/L represents advanced consumption and is a late and serious finding. Taken together, these four parameters capture the three axes of DIC pathophysiology: thrombin generation (PT, fibrin markers), platelet activation and consumption (platelet count), and fibrinolysis (fibrin markers, fibrinogen).
DIC phenotypes and treatment principles
The 2025 ISTH revision formally recognized two clinical phenotypes. Hemorrhagic DIC (consumption coagulopathy) occurs when factor and platelet depletion outpaces production, leading to clinical bleeding - petechiae, ecchymosis, bleeding from venipuncture sites, mucous membranes, or surgical wounds. Management focuses on treating the trigger, replacing consumed blood products (fresh frozen plasma for factor depletion, cryoprecipitate or fibrinogen concentrate for fibrinogen below 1.5 g/L, platelet transfusion for counts below 50 x 10⁹/L with bleeding), and avoiding unnecessary heparin. Thrombotic DIC is driven by excessive coagulation with suppressed fibrinolysis - it causes microvascular occlusion and end-organ dysfunction (purpura fulminans, acral ischemia, renal cortical necrosis) and is more likely in septic DIC. In this phenotype, anticoagulant therapy with unfractionated heparin or low-molecular-weight heparin may be considered if organ-threatening thrombosis outweighs bleeding risk. The ISTH score alone does not distinguish phenotype - clinical context is essential. All management decisions should involve hematology consultation.
ISTH DIC Scoring Parameters
| Parameter | Finding | Points |
|---|---|---|
| Platelet count | >= 100 x 10⁹/L | 0 |
| Platelet count | 50 to < 100 x 10⁹/L | 1 |
| Platelet count | < 50 x 10⁹/L | 2 |
| Fibrin markers (D-dimer / FDPs) | No increase | 0 |
| Fibrin markers (D-dimer / FDPs) | Moderate increase (approx. 3-7x ULN) | 2 |
| Fibrin markers (D-dimer / FDPs) | Strong increase (> 7x ULN) | 3 |
| PT prolongation | < 3 seconds above ULN | 0 |
| PT prolongation | 3 to < 6 seconds above ULN | 1 |
| PT prolongation | >= 6 seconds above ULN | 2 |
| Fibrinogen | >= 1 g/L | 0 |
| Fibrinogen | < 1 g/L | 1 |
| INTERPRETATION | Score >= 5: compatible with overt DIC | - |
| INTERPRETATION | Score < 5: not overt DIC; repeat in 24-48 h | - |
Each laboratory parameter is assigned points based on severity of abnormality. Maximum total score is 8. Adapted from the ISTH consensus guideline.
Frequently asked questions
What is the ISTH DIC score cut-off for overt DIC?
A score of 5 or higher on the 0-8 ISTH scale is considered compatible with overt DIC. This threshold was validated with 93% sensitivity and 98% specificity in the original cohort. Scores of 4 or below do not rule out DIC - they suggest possible non-overt (pre-overt) DIC and the score should be repeated in 24-48 hours with fresh laboratory values if clinical suspicion remains.
Can DIC occur with a normal platelet count?
Yes. In the early or compensated phase, platelet production can keep pace with consumption and the count may stay above 100 x 10⁹/L. This is why the ISTH algorithm incorporates three other parameters. A rising D-dimer and a shortened serial platelet trend - even within the normal range - can signal early DIC before counts fall below the scoring thresholds.
Why is D-dimer excluded from the DIC score in pregnancy?
D-dimer rises physiologically throughout normal pregnancy, particularly after 20 weeks gestation, because placental fibrinolysis continuously generates fibrin breakdown products. Using standard D-dimer thresholds in pregnant patients would produce false-positive scores. The pregnancy-adapted ISTH scoring algorithm therefore relies on platelets, PT prolongation, and fibrinogen only, and applies pregnancy-specific normal ranges for each parameter.
How often should the ISTH DIC score be repeated?
For patients with a score of 5 or above, repeat scoring every 24 hours to track treatment response and detect worsening. For patients with a score below 5 but ongoing clinical concern, repeat in 24-48 hours. In acutely deteriorating patients - particularly with septic shock or major trauma - laboratory parameters may change within hours and more frequent monitoring is appropriate based on clinical judgment.
What conditions most commonly trigger DIC?
Sepsis is the most common cause of DIC in intensive care units, accounting for about one-third of cases. Other major triggers include solid and hematologic malignancies (especially acute promyelocytic leukemia), major trauma with tissue destruction, obstetric complications (placental abruption, amniotic fluid embolism, HELLP syndrome), severe burns, major surgery, incompatible blood transfusions, and snakebite envenomation. Treatment of the underlying trigger is the cornerstone of DIC management - supportive measures alone are insufficient without addressing the driver.
Is the ISTH score the only diagnostic system for DIC?
No. Several systems exist alongside the ISTH overt DIC algorithm, including the Japanese Ministry of Health and Welfare (JMHW) score, the Japanese Association for Acute Medicine (JAAM) score, and the CDSS (Chinese DIC Scoring System). Each uses slightly different parameters and thresholds. The ISTH algorithm is the most widely adopted internationally and the most studied, but the JAAM criteria may identify DIC earlier in sepsis because they include a rapidly falling platelet count as a scored variable rather than relying solely on the absolute count.
Sources
- Taylor FB Jr, Toh CH, Hoots WK, et al. Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation. Thromb Haemost. 2001;86(5):1327-1330.
- Wada H, Thachil J, Di Nisio M, et al. Guidance for diagnosis and treatment of DIC from harmonization of the recommendations from three guidelines. J Thromb Haemost. 2013;11(4):761-767.