How to read a D-dimer result
Other platforms explain it with text and video. In VMS you practice it on the patient.
D-dimer is a piece of broken-down clot found in the blood. It is very good at ruling out a clot in low-risk patients and poor at proving one.
Step by step
Estimate pretest probability
Use a score such as Wells for leg clots (DVT) or lung clots (PE). In very low risk PE, the PERC rule may avoid testing at all. [1]
Order it only in low or moderate risk
If the probability is high, go straight to imaging. A negative D-dimer cannot safely rule out a clot in high-risk patients. [1]
Know the cut-off and units
Many labs use 500 ng/mL in fibrinogen equivalent units. Check the units, because some labs report D-dimer units, which are about half. [1]
Adjust for age
Over age 50, many use age times 10 ng/mL as the cut-off for suspected PE. This avoids extra scans in older adults. [1]
Read a negative result
A result below the cut-off in a low or moderate risk patient makes a clot very unlikely. Imaging is usually not needed. [2]
Read a positive result
A high result does not prove a clot. Pregnancy, surgery, cancer, infection and older age all raise it, so confirm with imaging. [2]
Explain and plan
Tell the patient what the test can and cannot show and arrange the next step. [3]
Common errors
- Ordering it in high-risk patients.
- Treating a positive result as proof of a clot.
- Ignoring the units and the age-adjusted cut-off.
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
- NCCPA PANCE Content Blueprint
- AAMC Core Entrustable Professional Activities (Core EPAs)
- AHRQ Health Literacy Universal Precautions Toolkit (Teach-Back)
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.