ISTH DIC Score Calculator
ISTH DIC Score Calculator
The 2025 ISTH overt DIC score, with the explicit 3× and 7× upper-limit multiples that replaced the old "moderate" and "strong" increase. Valid only in a patient who already has a disorder known to cause DIC.
ISTH DIC Score
4 items → 0–8Platelets 78 ×10⁹/L (1); D-dimer 5× the local upper limit (2); prothrombin time prolonged by 4 seconds (1); fibrinogen 2.4 g/L (0)
Scoring — 2025 ISTH revision
Platelets: under 50 ×10⁹/L = 2 · 50 to under 100 = 1 · 100 or above = 0
D-dimer: above 7× ULN = 3 · above 3× ULN = 2 · otherwise 0
Prothrombin time prolongation: 6 s or more = 2 · 3 to under 6 s = 1 · under 3 s = 0
Fibrinogen (Clauss): under 1 g/L = 1 · 1 g/L or above = 0
Maximum 8. A score of 5 or more is compatible with overt DIC.
- an underlying disorder first
- the ISTH algorithm begins by asking whether the patient has a disorder known to be associated with DIC — sepsis, major trauma, malignancy, obstetric catastrophe, severe pancreatitis, extensive burns. If not, the score is not applied. It is a confirmatory tool in a suspected population, never a screening test in an unselected one
- 3× and 7× YOUR upper limit
- the 2025 revision replaced the 2001 wording of a "moderate" or "strong" increase in fibrin-related markers with explicit multiples. That fixed the largest source of inter-observer variation, but the multiples are of the reporting laboratory's own upper limit — D-dimer assays differ several-fold in units and calibration, so an absolute number does not travel
- score it repeatedly
- DIC is a process, not a state. A single score below 5 does not exclude it and a score of 5 does not fix the diagnosis; the trajectory over serial measurements carries far more information than any one total
- what else changed in 2025
- the revision also rewrote the definition of DIC itself — an acquired, life-threatening intravascular disorder with systemic coagulation activation, dysregulated fibrinolysis and endothelial injury resulting in microthrombosis — and named two phenotypes, haemorrhagic and thrombotic, which behave and are treated differently
Worked example
Platelets 78 ×10⁹/L (1); D-dimer 5× the local upper limit (2); prothrombin time prolonged by 4 seconds (1); fibrinogen 2.4 g/L (0)
1 + 2 + 1 + 0 = 4 points
4 is below 5, so this does not meet the criteria for overt DIC today
It is not a negative result. One further point from anywhere — platelets under 50, D-dimer past 7× the upper limit, prothrombin time reaching 6 seconds prolonged, or fibrinogen below 1 g/L — makes this overt DIC, so the score should be repeated
Fibrinogen scores 0 at 2.4 g/L. But fibrinogen is an acute-phase reactant: in sepsis a level inside the reference interval may already be a large fall from a raised baseline, and the direction of travel matters more than the single value
The D-dimer was scored as a multiple of the local upper limit, not as an absolute number. The same plasma reported by two laboratories can differ several-fold in the printed figure
The four items — 2025 ISTH revision
| Item | 3 points | 2 points | 1 point | 0 points |
|---|---|---|---|---|
| Platelet count | — | Under 50 ×10⁹/L | 50 to under 100 ×10⁹/L | 100 ×10⁹/L or above |
| D-dimer or fibrin-related marker | Above 7× the upper limit of normal | Above 3× the upper limit of normal | — | 3× the upper limit or below |
| Prothrombin time prolongation | — | 6 seconds or more | 3 to under 6 seconds | Under 3 seconds |
| Fibrinogen (Clauss) | — | — | Under 1 g/L (under 100 mg/dL) | 1 g/L or above |
Before the score: does this patient qualify for it?
| Question | Answer |
|---|---|
| Is an underlying disorder required? | Yes. The ISTH algorithm applies only to patients with a condition known to cause DIC — sepsis, major trauma, malignancy including acute promyelocytic leukaemia, obstetric emergencies such as abruption or amniotic fluid embolism, severe pancreatitis, extensive burns, severe liver disease, some envenomations. |
| Is it a screening test? | No. In an unselected patient with an abnormal clotting screen, the score has no validated meaning and will label liver disease, dilution and vitamin K deficiency as DIC. |
| Can one score make the diagnosis? | No. DIC is a process. The score is designed to be repeated, and the trajectory carries far more information than any single total. |
| What did the 2025 revision change? | It redefined DIC as an acquired, life-threatening intravascular disorder with systemic coagulation activation, dysregulated fibrinolysis and endothelial injury resulting in microthrombosis; it named haemorrhagic and thrombotic phenotypes; and it replaced the vague fibrin-marker wording with the explicit 3× and 7× multiples. |
| Does it apply in pregnancy? | Not without modification. D-dimer rises physiologically through pregnancy and fibrinogen runs high, so the standard thresholds mislead in both directions; pregnancy-specific DIC scores that omit D-dimer exist for this reason. |
A confirmatory score, not a screening test
Disseminated intravascular coagulation is a complication of something else. The ISTH scoring system was built on that premise, and its algorithm opens with a question that is not a laboratory one: does this patient have an underlying disorder known to be associated with DIC? Sepsis, major trauma, malignancy, an obstetric catastrophe, severe pancreatitis, extensive burns. If the answer is no, the score is not applied. Run on an unselected patient with an abnormal clotting screen it will confidently label liver disease, haemodilution and vitamin K deficiency as DIC, because those produce the same numbers.
Given that precondition, four laboratory items are scored: the platelet count, a fibrin-related marker such as the D-dimer, the prolongation of the prothrombin time, and the Clauss fibrinogen. The maximum is 8, and 5 or more is compatible with overt DIC. The 2025 revision changed the second of those items in a way that matters. The 2001 criteria asked only whether the fibrin-related marker showed a "moderate" or a "strong" increase, wording that different assessors read differently and that no laboratory could operationalise. The revision replaced it with explicit multiples: above three times the upper limit of normal scores 2, above seven times scores 3.
Those are multiples of the reporting laboratory’s own upper limit, and that qualification is the whole point of the change. D-dimer assays differ several-fold in their units and calibration, so the same plasma returns very different absolute numbers in different hospitals and no absolute threshold could ever have travelled. The 2025 revision also rewrote the definition of DIC itself, describing it as an acquired, life-threatening intravascular disorder with systemic coagulation activation, dysregulated fibrinolysis and endothelial injury resulting in microthrombosis, and named two phenotypes — haemorrhagic and thrombotic — that behave and are managed differently.
Two habits make the score more useful. Repeat it: DIC is a process, a score of 4 today is not a negative result, and the trajectory over serial measurements says more than any single total. And read fibrinogen with suspicion, because it is an acute-phase reactant — a level inside the reference interval during sepsis may already represent a large fall from a raised baseline, and it will score 0 while doing so. The score supports a clinical judgement about a patient who is already unwell for a known reason; it does not replace it, and no threshold in it should be read as a rule.
Frequently asked questions
What ISTH DIC score indicates overt DIC?
Five or more out of a maximum of 8 is compatible with overt disseminated intravascular coagulation. Below 5 does not exclude it — the score is designed to be repeated as the illness evolves, and a total of 4 is one point away in any of the four items.
Can the ISTH DIC score be used as a screening test?
No. The algorithm applies only to patients who already have a disorder known to cause DIC — sepsis, major trauma, malignancy, an obstetric emergency, severe pancreatitis, extensive burns. In an unselected patient with an abnormal clotting screen it will label liver disease, dilution and vitamin K deficiency as DIC.
What changed in the 2025 ISTH revision?
The fibrin-related marker item was rewritten from a vague "moderate" or "strong" increase into explicit multiples — above 3 times the upper limit of normal scores 2, above 7 times scores 3. The revision also redefined DIC itself and named haemorrhagic and thrombotic phenotypes.
Which D-dimer value scores 2 points?
Any result above three times your own laboratory’s upper limit of normal, and above seven times scores 3. There is no absolute number: D-dimer assays differ several-fold in units and calibration, so the multiple has to be worked out against the upper limit printed on your report.
Why does a normal fibrinogen not exclude DIC?
Because fibrinogen is an acute-phase reactant and rises in inflammation. In sepsis a level inside the reference interval may already be a large fall from a considerably raised baseline, and it scores 0 on this item while doing so. The trend across serial measurements is more informative than any single value.
Related calculators
References
- Iba T, Levy JH, Maier CL, et al. Updated definition and scoring of disseminated intravascular coagulation in 2025: communication from the ISTH SSC Subcommittee on Disseminated Intravascular Coagulation. J Thromb Haemost. 2025;23(7):2356–2362.
- Taylor FB Jr, Toh CH, Hoots WK, Wada H, Levi M. Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation. Thromb Haemost. 2001;86(5):1327–1330.
- Levi M, Toh CH, Thachil J, Watson HG. Guidelines for the diagnosis and management of disseminated intravascular coagulation. Br J Haematol. 2009;145(1):24–33.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.