Coagulation & Thrombosis
Every coagulation & thrombosis calculator on CalcEngines — unit converters, derived indices and interpretive tools, each with its formula, a worked example and the reference intervals it is judged against.
23 calculators in this section
- 4Ts Score for HIT CalculatorScore the four Ts for heparin-induced thrombocytopenia. A low score carries a negative predictive value of about 0.998, so this is a rule-out tool — and an intermediate or high score never rules HIT in.
- Age-Adjusted D-Dimer CalculatorApply the age-adjusted D-dimer cut-off — age × 10 µg/L FEU above age 50 — to avoid unnecessary imaging in older patients with a non-high pre-test probability.
- Antithrombin Activity Unit ConverterConvert antithrombin activity between %, IU/mL and proportion — 1.00 IU/mL is by definition 100% of pooled normal plasma — and see why the result must not be measured during an acute thrombosis or on heparin.
- aPTT Ratio CalculatorExpress a patient aPTT against your laboratory's mean normal as a ratio — the only form in which the result travels between laboratories.
- CHA₂DS₂-VASc and CHA₂DS₂-VA Score CalculatorStroke risk in atrial fibrillation on either convention. The 2024 ESC guideline dropped the sex category and moved to CHA₂DS₂-VA; the two age items are alternatives, so the real maximum is 9, not the 10 the weights add up to.
- Coagulation Mixing Study InterpreterMix patient plasma 1:1 with normal plasma and repeat the aPTT. Correction means a factor is missing; failure to correct means something is inhibiting one. This page computes the Rosner index and the percent correction, and uses the incubated mix to separate a factor VIII inhibitor from a lupus anticoagulant.
- D-Dimer FEU to DDU ConverterConvert D-dimer between fibrinogen equivalent units and D-dimer units — two incompatible reporting systems that, confused, either miss a pulmonary embolism or trigger an unnecessary CT scan.
- Fibrinogen Unit ConverterConvert fibrinogen between g/L, mg/dL and µmol/L, with the replacement thresholds and the reason a Clauss result and a PT-derived result are not interchangeable.
- HAS-BLED Score CalculatorBleeding risk on anticoagulation for atrial fibrillation, with the two doubled letters scored properly. A high score flags what to correct and who to review — it is not a reason to withhold anticoagulation.
- Heparin Anti-Xa Unit ConverterConvert heparin anti-Xa activity between IU/mL and IU/L, with the target ranges separated by drug and by sample — because the assay must be calibrated for the heparin being given, and a result read against the other drug's range is a real error.
- INR Calculator (from PT and ISI)Convert a patient's prothrombin time into an INR using the laboratory's mean normal PT and the reagent's ISI — the calculation that makes PT results comparable between laboratories and reagents.
- ISTH DIC Score CalculatorThe 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.
- Padua Prediction Score CalculatorVenous thromboembolism risk in hospitalised medical patients. Four items score 3 points each, so the threshold of 4 is reached faster than it looks — one major risk factor and one ordinary comorbidity.
- PERC Rule CalculatorApply the Pulmonary Embolism Rule-out Criteria to avoid any further testing — not even a D-dimer — in patients whose gestalt pre-test probability of PE is already low.
- Prolonged PT or APTT Interpreter — Which Factor, Which Next TestEnter whether the PT and the APTT are prolonged against your laboratory's intervals, with the context that changes the answer — anticoagulants including DOACs, liver disease, bleeding or an acutely unwell patient, a known lupus anticoagulant, a doubtful sample. It names the pathway, the factors that could be low and the next test, including the prolonged APTT that never bleeds (factor XII) and the one that is an emergency (acquired haemophilia A).
- Prothrombin Time to Quick % ConverterA German report of "Quick 70%" and a British report of "INR 1.2" describe the same patient. This page maps a prothrombin time in seconds onto the Quick value in per cent, using your own laboratory's calibration anchors — and is honest that the mapping is an approximation, because the Quick curve is not a formula.
- Simplified PESI (sPESI) CalculatorPrognosis after a confirmed pulmonary embolism, not diagnosis of one. Six items, one point each — and only a score of zero identifies the low-risk group that may be considered for outpatient management.
- Thrombin Time InterpreterA prolonged thrombin time has two classic causes and one modern one: heparin in the sample, a problem with fibrinogen, and dabigatran. This page works out which, from the thrombin time, the reptilase time and the fibrinogen — and a normal result is worth as much as an abnormal one.
- VWF Activity to Antigen Ratio CalculatorDivide von Willebrand factor activity by von Willebrand factor antigen. A ratio below 0.7 says the factor present is not working properly — a qualitative type 2 defect rather than simply having too little of it, which changes the treatment.
- Warfarin Dose Adjustment by INRWhere an INR sits against its target range, and what the guidelines actually say to do about it — including the most useful answer, which is often to change nothing. Warfarin's effect lags by days, so dose changes are judged on the weekly total rather than on a single reading.
- Weight-Based Heparin Nomogram CalculatorAdjust an unfractionated heparin infusion from the aPTT ratio using the Raschke weight-based nomogram — and check first that the ratio target belongs to your laboratory, because a target borrowed from another hospital can be materially wrong.
- Wells Score for DVT CalculatorEstimate the clinical probability of deep vein thrombosis with the Wells score, using the two-level DVT-unlikely / DVT-likely interpretation current guidance recommends.
- Wells Score for PE CalculatorEstimate the clinical probability of pulmonary embolism with the Wells score, using the two-level PE-unlikely / PE-likely interpretation that pairs with D-dimer or goes straight to CT.