🫁 D-dimer Testing Diagnostic Pathway Simulator

Wells Score Selects Low-Risk Patients for D-dimer Testing

Low clinical suspicion patients are screened before any blood draw.

• ≤4: Wells score cutoff (low/moderate PE probability)
• ~10%: Low-risk prevalence (actual PE in this group)
• Only if low risk: Test appropriateness (skips high-risk patients)
• Avoid unneeded CT: Goal (in low-probability patients)

Wells criteria overview

Clinical signs, symptoms, and risk factors scored briefly.

Why gate testing by risk

D-dimer only useful when pretest probability is low.

D-dimer Blood Test Quantifies Fibrin Degradation Products

A quantitative ELISA or immunoturbidimetric assay reports ng/mL level.

• ELISA / turbidimetric: Assay type (quantitative D-dimer)
• ng/mL FEU: Units (fibrinogen equivalent units)
• ~1 hour: Turnaround (rapid lab result)
• >95%: Sensitivity (high negative predictive value)

What D-dimer measures

Cross-linked fibrin breakdown fragment from clot turnover.

Confounders

Age, pregnancy, inflammation, cancer raise baseline levels.

Age-Adjusted Cutoff Replaces the Fixed 500 ng/mL Rule

Patients over 50 use age×10 ng/mL instead of a flat 500.

• 500 ng/mL: Standard cutoff (used under age 50)
• age × 10: Age-adjusted formula (ng/mL, for age >50)
• 800 ng/mL: Example at 80 (vs. flat 500 threshold)
• ADJUST-PE, 2014: Validation study (JAMA multicenter trial)

Why D-dimer rises with age

Baseline coagulation activity increases naturally over decades.

Formula in practice

Multiply age by ten once patient passes fifty.

Below Threshold Rules Out PE; Above Threshold Triggers CTPA

A single comparison decides imaging versus discharge without a scan.

• PE ruled out: Below threshold (no further imaging needed)
• CTPA ordered: Above threshold (CT pulmonary angiography)
• <1%: Missed PE risk (when rule-out criteria met)
• Single comparison: Decision basis (level vs. threshold line)

Ruling out pathway

Below-threshold patients are discharged without CT scan.

Imaging pathway

Above-threshold patients proceed to CT angiography confirmation.

Age Adjustment Reduces Unnecessary CT Scans in Older Patients

Fewer older patients get scanned, without increasing missed PE cases.

• ~14%: CT scans avoided (additional in older cohorts)
• <1%: Missed PE at 3 months (safety endpoint unchanged)
• Yes: Radiation avoided (per unnecessary CT skipped)
• Yes: Contrast risk avoided (nephropathy, allergy exposure)

Population-level benefit

Older cohorts see the largest drop in scan rate.

Safety maintained

Outcome studies show no rise in missed embolism.