How this instrument works
Disseminated intravascular coagulation is a condition in which clotting activates throughout the bloodstream at once, consuming platelets and clotting factors faster than the body can replace them and leaving a patient prone to both clotting and bleeding simultaneously. In 2001, the Scientific and Standardisation Committee on DIC of the International Society on Thrombosis and Haemostasis published a scoring system that turns four lab values a clinician has typically already ordered into a single number describing how consistent the pattern is with overt DIC.
The four components are platelet count, a fibrin-related marker such as D-dimer, prothrombin time, and fibrinogen level, each assigned points based on how abnormal the result is — more severe derangement earns more points, and the four scores sum to a total between 0 and 8. The original paper describes a total of 5 or higher as compatible with a diagnosis of overt DIC, while a lower score suggests the pattern isn't there yet, or that DIC is present in a non-overt, earlier form.
This score only sums numbers a clinician has already measured; it does not run a test of its own, and it is meant to be applied specifically in patients who already have an underlying condition known to trigger DIC, such as sepsis, major trauma, or certain cancers, rather than as a general screening tool. A score below 5 is commonly followed by repeating the panel in a day or two, since DIC can develop or worsen quickly, and a single below-threshold reading doesn't rule out a diagnosis that later labs might support.
- Select Platelet count — over 100×10⁹/L, 50-100×10⁹/L, or under 50×10⁹/L.
- Select Fibrin-related marker (D-dimer/FDP) — no increase, moderate increase, or strong increase.
- Select Prolonged prothrombin time — under 3 seconds, 3-6 seconds, or over 6 seconds.
- Select Fibrinogen level — over 1 g/L, or 1 g/L or under.
- Read the ISTH overt DIC score (0-8); a total of 5 or higher is compatible with overt DIC.
Worked example — three ISTH overt DIC scores
Platelets under 50 (2 points), a strong fibrin-marker increase (3 points), PT prolonged over 6 seconds (2 points), and fibrinogen at or under 1 g/L (1 point): total = 2 + 3 + 2 + 1 = 8, the maximum possible score and well above the ≥5 threshold described as compatible with overt DIC.
Every component at its mildest — platelets over 100 (0 points), no fibrin-marker increase (0 points), PT prolonged under 3 seconds (0 points), fibrinogen over 1 g/L (0 points): total = 0 + 0 + 0 + 0 = 0, the lowest possible score and not compatible with overt DIC by this system.
Platelets in the 50-100 range (1 point), a moderate fibrin-marker increase (2 points), PT prolonged 3 to 6 seconds (1 point), and normal fibrinogen over 1 g/L (0 points): total = 1 + 2 + 1 + 0 = 4, just under the ≥5 threshold — a pattern the original scoring system suggests be repeated in a day or two rather than treated as confirming overt DIC.
Questions
What does a total ISTH score of 5 or higher mean?
It means the pattern of lab values is compatible with overt disseminated intravascular coagulation, per the threshold the ISTH Scientific Subcommittee set when the scoring system was published in 2001. It describes consistency with the diagnosis, read alongside the patient's clinical condition, rather than a standalone confirmation that overrides clinical judgment.
What should happen if the score comes out below 5?
A score under 5 suggests the pattern isn't yet compatible with overt DIC, and the scoring system's authors recommend repeating the same panel over the following day or two, since the underlying process can progress quickly in a patient who already has a condition known to trigger DIC. A single reassuring score early on doesn't rule out DIC developing shortly after.
Why does a strong fibrin-marker rise earn more points than a low platelet count?
Because the original scoring system weighted each component by how specifically it reflects the widespread clotting activation seen in DIC, not just by how abnormal the number looks. A strong rise in a fibrin-related marker such as D-dimer earns 3 points at its worst, one more than the maximum 2 points for platelets or prothrombin time, reflecting how the ISTH committee calibrated these weights against outcomes in its original work.
Can this score be used on any patient with abnormal coagulation labs?
No — it's designed specifically for patients who already have an underlying condition recognized to cause DIC, such as sepsis, trauma, or certain malignancies. Applying the score outside that context, to abnormal coagulation from an unrelated cause, wasn't how the scoring system was validated and can produce a misleading result.
Does this calculator diagnose DIC?
No — it only adds four numbers you select from a lab report. The ISTH scoring system it implements is described by its own authors as a decision-support aid meant to be read alongside the full clinical picture, not a stand-alone diagnostic test, and confirming or ruling out DIC remains a decision made by the treating clinical team.
What labs feed into the fibrin-related marker component?
Most commonly D-dimer, though the original scoring system allows other fibrin degradation product assays as well, graded as no increase, a moderate increase, or a strong increase based on cutoffs each laboratory sets against its own assay. Because assays and cutoffs vary between labs, the same patient's blood tested at two different laboratories can occasionally score this component differently.
References
- Taylor et al. 2001, Thromb Haemost — ISTH DIC score (PubMed)
- MDCalc — ISTH Criteria for Disseminated Intravascular Coagulation
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.