What is a normal D-dimer (D-dimer) level?

From the Guidelines

A normal D-dimer level is typically less than 500 ng/mL (or 0.5 μg/mL), though this can vary slightly depending on the specific laboratory and testing method used. D-dimer is a protein fragment produced when a blood clot dissolves in the body. It's measured through a simple blood test and serves as an important screening tool for ruling out thrombotic conditions like deep vein thrombosis (DVT) and pulmonary embolism (PE) 1. The main value of D-dimer testing lies in its high sensitivity and negative predictive value—a normal result effectively rules out thrombosis in patients with low clinical probability. However, D-dimer levels naturally increase with age, so some clinicians use an age-adjusted cutoff (age × 10 ng/mL for patients over 50) for more accurate interpretation 1. It's essential to consider that while a normal D-dimer can help exclude clotting disorders, an elevated level doesn't necessarily confirm them, as many conditions including pregnancy, inflammation, infection, cancer, and recent surgery can cause elevated D-dimer levels without thrombosis 1.

Some key points to consider:

• D-dimer testing is most useful in patients with low clinical probability of PE, as a normal result can effectively rule out the condition.
• The age-adjusted cutoff (age × 10 ng/mL for patients over 50) can be used for more accurate interpretation in older patients.
• Elevated D-dimer levels can be caused by various conditions other than thrombosis, such as pregnancy, inflammation, infection, cancer, and recent surgery.
• The negative predictive value of D-dimer testing is high, but the positive predictive value is low, making it less useful for confirmation of PE.

Overall, a normal D-dimer level is less than 500 ng/mL, and its interpretation should be considered in the context of the patient's clinical presentation and other diagnostic findings.

From the Research

D-dimer Levels

• A normal D-dimer level can vary depending on the assay used and the clinical context, but common cutoff values include:
  • 500 micrograms/L (or 500 ng/mL) as a threshold below which deep vein thrombosis (DVT) or pulmonary embolism (PE) can be ruled out 2, 3
  • 1000 ng/mL as a threshold below which PE can be ruled out in patients with a low clinical pretest probability (C-PTP) 4
• Elevated D-dimer levels can be caused by various conditions, including tissue injury, cancer, and thromboembolic phenomena 5, 3
• The positive predictive value of D-dimer levels increases with higher concentrations, improving the ability to identify diseases with high thrombus burden 5

Clinical Context

• In outpatients with suspected PE, a D-dimer level below 500 micrograms/L may allow the exclusion of PE, with a negative predictive value of 99% 2
• In patients with a low C-PTP and a D-dimer level of less than 1000 ng/mL, or with a moderate C-PTP and a D-dimer level of less than 500 ng/mL, PE can be ruled out without further testing 4
• D-dimer testing may suffer from diagnostic errors occurring throughout the pre-analytical, analytical, and post-analytical phases of the testing process 6

Assay-Specific Considerations

• Different D-dimer assays may have varying cutoff values and diagnostic performances 6
• Local guidance should be applied when interpreting D-dimer test results, taking into account the specific assay used and the clinical context 6