Thrombophilia Calculator

Should I Test for Thrombophilia?

Evidence-based decision support for thrombophilia testing and treatment

How to Use This Tool

1 Search by keywords or select from dropdown

2 Review the recommended action

3 Adjust parameters to see how they affect the decision

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R1 Anticoagulation Decision

Clinical Scenario

Description will appear here...

Recommendation

Test for Thrombophilia

Based on decision analysis, testing is recommended for this scenario.

Decision Model Test

ASH Guideline Test

Full ASH Recommendation

ASH recommendation text will appear here...

View detailed analysis

Decision Thresholds

Current VTE Risk 10%

Testing Zone 0.52% – 0.86% Test only if VTE risk is in this range

Treat all if above 0.86%

Expected Outcomes per 1,000 Patients

Strategy	VTE Events	Major Bleeds
Don't Treat	100	5
Test First	57	7
Treat All	15	11

Expected Utility Graph

Adjust Parameters

VTE Risk (%)

Patient Preference (RV) 1 = equal weight to VTE and harms

Bleeding Risk

About This Tool

Purpose

This calculator provides evidence-based decision support for thrombophilia testing and treatment decisions based on the American Society of Hematology (ASH) 2023 Guidelines. It implements a decision-theoretical framework that makes explicit the trade-offs between benefits and harms of testing and treatment.

The Threshold Approach

Clinical decisions can be framed using decision thresholds—probability cutoffs that determine when the expected benefits of an action outweigh its expected harms.

Don't Treat VTE risk too low to justify treatment harms

Testing Threshold

Test First Testing can identify who benefits from treatment

Treatment Threshold

Treat All VTE risk high enough to treat without testing

Key Decision Rules for Standard Recommendations (R1-R14, R21-R23)

No testing/no treatment: VTE risk < Testing threshold
Thrombophilia testing: Testing threshold < VTE risk < Treatment threshold
Treatment with anticoagulants: VTE risk > Treatment threshold

Key Decision Rules for R15-R20 (Inverse Logic)

For recommendations R15-R20 (women considering COC/HRT), the logic is reversed because hormonal treatment increases VTE risk rather than reducing it:

Treatment (COC/HRT): VTE risk < Treatment threshold — the best strategy is to not test and administer treatment
Thrombophilia testing: Treatment threshold < VTE risk < Testing threshold — the best strategy is to test and treat if the test is negative
No testing/no treatment: VTE risk > Testing threshold — the best strategy is to not test and avoid treatment

The thresholds are calculated using Expected Utility Theory (EUT), weighing:

Probability of VTE without treatment
Relative risk reduction from anticoagulation (or increase from hormones)
Bleeding risk from treatment (or pregnancy/symptom costs)
Test characteristics (prevalence, relative risk in positives)
Patient preferences (relative value of avoiding VTE vs. harms)

Two Types of Decisions

Anticoagulation Decisions (R1-R14, R21-R23)

Trade-off: VTE prevention vs. Bleeding risk

Treatment (anticoagulation) reduces VTE but increases bleeding. Higher VTE risk favors treatment.

COC/HRT Decisions (R15-R20)

Trade-off: VTE risk vs. Contraceptive/HRT benefits

Treatment (hormones) increases VTE risk but provides benefits. This creates reversed decision logic—lower VTE risk favors using COC/HRT.

Mathematical Foundation

The treatment threshold (P_t) is derived from the point where expected utility of treatment equals expected utility of no treatment:

P_t = RV × (RR_bleed - 1) × H / (1 - RR_rx)

Where RV = relative value of outcomes, H = baseline bleeding risk, RR = relative risks.

The testing threshold (P_tt) accounts for test characteristics to identify the range where testing provides value.

Quality of Evidence

Quality (certainty) of evidence (CoE) is judged by the ASH thrombophilia panel as very low for all recommendations except for R15 and R16, which the panel judged as low CoE.

For all scenarios considered, the panel made conditional recommendations except for R15, which strongly recommended not testing for thrombophilia to guide COC use in women from the general population.

References

Djulbegovic B, Hozo I, Guyatt G. Decision-theoretical foundations of the ASH thrombophilia guidelines. Blood Advances. 2024. doi:10.1182/bloodadvances.2024012931
Pauker SG, Kassirer JP. The threshold approach to clinical decision making. N Engl J Med. 1980;302:1109-1117.
ASH Guidelines on Thrombophilia Testing. Blood Advances. 2023.

Color Legend

Green: Treatment recommended

Yellow: Testing recommended first

Red: No treatment recommended

Model vs Excel Agreement Verification

Case	pVTE (%)	Ptt (%)	Pt (%)	Excel EUT	Model EUT	ASH	Match?