Introduction
The ISTH DIC score is a diagnostic scoring system used to identify overt disseminated intravascular coagulation (DIC), a condition in which widespread activation of the clotting system consumes platelets and clotting factors faster than the body can replace them. This leads to a dangerous combination of simultaneous clotting and bleeding, and it can rapidly progress to organ damage if unrecognized.
The score works by grading four routine laboratory tests, platelet count, a fibrin-related marker such as D-dimer, prothrombin time (PT) prolongation, and fibrinogen level, and summing them into a single total from 0 to 8. It was developed by the International Society on Thrombosis and Haemostasis (ISTH) Scientific and Standardization Committee in 2001, specifically for use in patients who already have a condition known to trigger DIC, such as sepsis, trauma, malignancy, or obstetric complications [1,2].
It is used mainly by hematologists, intensivists, and emergency physicians managing critically unwell patients, and it is repeated daily to track whether coagulopathy is worsening or improving.
The ISTH DIC Score Criteria
The score can only be applied in a patient with a known underlying disorder associated with DIC. Applying it to an isolated abnormal lab value in an otherwise well patient is not valid.
| Parameter | Result | Points |
|---|---|---|
| Platelet count | > 100 × 10⁹/L | 0 |
| 50–100 × 10⁹/L | 1 | |
| < 50 × 10⁹/L | 2 | |
| Fibrin-related marker(e.g., D-dimer, fibrin degradation products) | No increase | 0 |
| Moderate increase | 2 | |
| Strong increase | 3 | |
| Prolonged PT | < 3 seconds above normal | 0 |
| 3–6 seconds above normal | 1 | |
| > 6 seconds above normal | 2 | |
| Fibrinogen level | > 1.0 g/L | 0 |
| < 1.0 g/L | 1 |
The maximum possible score is 8. The fibrin-related marker carries the most weight of any single component, up to 3 points, so a strongly elevated D-dimer alone moves a patient a long way toward the diagnostic threshold. Cutoffs for “moderate” versus “strong” increase in the fibrin marker are set relative to the local laboratory’s reference range, since assay methods vary between institutions.
ISTH DIC Score Calculator
ISTH DIC Score Calculator
For use in patients with a known underlying disorder associated with DIC.
Total Score: 0
Suggestive of non-overt DIC
Interpreting the ISTH DIC Score
- Score ≥ 5 → Compatible with overt DIC. This reflects the decompensated phase of the syndrome, where the coagulation system’s compensatory mechanisms have been overwhelmed. The score should be repeated daily to track progression or response to treatment.
- Score < 5 → Suggestive of non-overt (compensated) DIC, not affirmative. The patient’s hemostatic system is under stress but still compensating. The score should be repeated in 1 to 2 days, or sooner if the clinical picture worsens.
Higher scores are also associated with worse outcomes: in published cohorts, rising ISTH DIC scores track with increased mortality, making the tool useful not just for diagnosis but for following disease severity over time, similar to how the SOFA score tracks organ dysfunction in critical illness.
The Pregnancy-Modified ISTH DIC Score
Because normal pregnancy naturally increases fibrinogen (normal range in late pregnancy is 3.0 to 6.0 g/L) and alters other baseline hemostatic parameters, applying the standard 2001 score often delays diagnosis. Modern obstetric practice uses a modified scoring system [3]:
| Parameter | Result | Points |
|---|---|---|
| Platelet count | > 100 × 10⁹/L | 0 |
| 50–100 × 10⁹/L | 1 | |
| < 50 × 10⁹/L | 2 | |
| Fibrinogen | ≥ 3.0 g/L | 0 |
| < 3.0 g/L | 1 | |
| PT difference | ≤ 1.0 seconds | 0 |
| > 1.0 seconds | 0.5 | |
| > 1.5 seconds | 1 |
The Pregnancy-Modified ISTH DIC Score Calculator
Pregnancy-Modified DIC Score
For use in obstetric emergencies (e.g., placental abruption, PPH).
Total Score: 0
Non-overt DIC
The Sepsis-Induced Coagulopathy (SIC) Score
Fibrinogen is an acute-phase reactant that surges during systemic inflammation, meaning it often remains falsely elevated in septic patients until they reach terminal DIC. To catch coagulation failure earlier, the ISTH introduced the SIC score in 2017 [4]:
| Parameter | Result | Points |
|---|---|---|
| Platelet count | ≥ 150 × 10⁹/L | 0 |
| 100–149 × 10⁹/L | 1 | |
| < 100 × 10⁹/L | 2 | |
| PT-INR | ≤ 1.2 | 0 |
| > 1.2 to 1.4 | 1 | |
| > 1.4 | 2 | |
| SOFA Score (excluding coagulation) | 0 | 0 |
| 1 | 1 | |
| ≥ 2 | 2 |
Sepsis-Induced Coagulopathy Score Calculator
SIC Score Calculator
Sepsis-Induced Coagulopathy assessment.
Total Score: 0
No SIC Indicated
Case Scenarios
Scenario 1: Non-overt DIC, repeat testing
A 45-year-old man is admitted with severe community-acquired pneumonia and early signs of sepsis. His platelet count is 130 × 10⁹/L, D-dimer shows a moderate rise, his PT is prolonged by 2 seconds, and fibrinogen is 1.4 g/L.
Calculator Exercise: What is his total score?
Clinical Interpretation: platelets (0, > 100), fibrin marker (2, moderate rise), PT (0, < 3 s prolongation), fibrinogen (0, > 1.0 g/L) = ISTH DIC score = 2 → suggestive of non-overt DIC. The score is repeated in 24 to 48 hours while sepsis treatment continues, since this is below the threshold for overt DIC but still reflects early hemostatic stress.
Scenario 2: Overt DIC in obstetric hemorrhage
A 32-year-old woman develops sudden, severe postpartum hemorrhage due to placental abruption. Her platelet count drops to 45 × 10⁹/L, PT is prolonged by 7 seconds, and fibrinogen falls to 0.8 g/L.
Calculator Exercise: What is her total score?
Clinical Interpretation: platelets (2, < 50), PT (1, > 1.5 s prolongation), fibrinogen (1, < 3.0 g/L) = Pregnancy-Modified ISTH DIC score = 4. Because the score is ≥ 2.6, this confirms overt DIC. Note that under standard criteria, a fibrinogen of 0.8 g/L only yields 1 point, but in pregnancy, this is a catastrophic drop from a baseline of 4.0+ g/L, requiring massive transfusion protocols.
Scenario 3: Overt DIC in sepsis, borderline threshold
A 68-year-old man in the ICU with septic shock from a perforated bowel has a platelet count of 70 × 10⁹/L, a PT-INR of 1.6, and a respiratory/cardiovascular SOFA score of 4.
Calculator Exercise: What is his total score?
Clinical Interpretation: platelets (2, < 100), PT-INR (2, > 1.4), SOFA (2, ≥ 2) = SIC score = 6. A SIC score ≥ 4 confirms sepsis-induced coagulopathy. Even if his standard ISTH score is below 5 due to elevated acute-phase fibrinogen, he already meets the criteria for early coagulation failure and requires immediate management of the underlying infection and coagulopathy.
Limitations of the ISTH DIC Score
The score is only valid in patients with a recognized DIC-associated condition; it should not be applied to isolated abnormal coagulation results in patients without a plausible trigger. PT prolongation and low fibrinogen can also reflect unrelated conditions like liver disease or warfarin therapy, which can confound interpretation.
Because fibrinogen acts as an acute-phase reactant and baseline coagulation parameters shift dynamically in certain patient populations, applying the 2001 score uniformly can be dangerous. As a result, standard practice now requires the use of the Sepsis-Induced Coagulopathy (SIC) score for septic patients [4] and the pregnancy-modified ISTH DIC score for obstetric patients [3]. Furthermore, the lack of international standardization for "moderate" versus "strong" fibrin-related marker increases continues to cause inter-institutional discrepancies in real-world scoring.
Disclaimer: This article is intended for educational and informational purposes only. It is not intended to be a substitute for informed professional medical advice, diagnosis, or treatment. While the information presented here is derived from credible medical sources and is believed to be accurate and up-to-date, it is not guaranteed to be complete or error-free. See additional information.
References
- Taylor, F. B., Jr, Toh, C. H., Hoots, W. K., Wada, H., Levi, M., & Scientific Subcommittee on Disseminated Intravascular Coagulation (DIC) of the International Society on Thrombosis and Haemostasis (ISTH) (2001). Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation. Thrombosis and haemostasis, 86(5), 1327–1330.
- Levi, M., Toh, C. H., Thachil, J., & Watson, H. G. (2009). Guidelines for the diagnosis and management of disseminated intravascular coagulation. British Committee for Standards in Haematology. British journal of haematology, 145(1), 24–33. https://doi.org/10.1111/j.1365-2141.2009.07600.x
- Erez, O., Othman, M., Rabinovich, A., Leron, E., Gotsch, F., & Thachil, J. (2022). DIC in Pregnancy - Pathophysiology, Clinical Characteristics, Diagnostic Scores, and Treatments. Journal of blood medicine, 13, 21–44. https://doi.org/10.2147/JBM.S273047
- Iba, T., Nisio, M. D., Levy, J. H., Kitamura, N., & Thachil, J. (2017). New criteria for sepsis-induced coagulopathy (SIC) following the revised sepsis definition: a retrospective analysis of a nationwide survey. BMJ open, 7(9), e017046. https://doi.org/10.1136/bmjopen-2017-017046
