D-dimer test: What it is, when it's used, and what your results mean

When your doctor suspects a D-dimer test, a blood test that measures a protein fragment released when a clot breaks down. It's also known as a D-dimer assay, and it's one of the first tools used to rule out dangerous clots like deep vein thrombosis or pulmonary embolism. This isn't a test that confirms a clot—it’s a gatekeeper. If your D-dimer level is normal and you're low risk, chances are you don’t have a clot, and you can skip more invasive scans.

High D-dimer levels don’t mean you definitely have a clot. They just mean something in your body is breaking down clots. That could be a deep vein thrombosis, a pulmonary embolism, or even pregnancy, surgery, infection, cancer, or advanced age. That’s why doctors always look at your symptoms, risk factors, and medical history alongside the result. A venous thromboembolism, a term that covers both deep vein clots and lung clots is the main concern when D-dimer is elevated. But if you’re healthy, young, and have no swelling or shortness of breath, a high D-dimer might just be noise. On the flip side, if you’ve just had surgery, are on long flights, or have cancer, even a slightly raised level can be a red flag.

Doctors use the D-dimer test because it’s fast, cheap, and avoids unnecessary radiation from CT scans. But it’s not perfect. Older adults often have mildly elevated levels naturally, so the threshold for what’s "normal" changes with age. Some hospitals use age-adjusted cutoffs to reduce false positives. The test also can’t tell you where the clot is, how big it is, or how old it is. That’s why a negative result is powerful—it lets you walk away from worry—but a positive one usually leads to an ultrasound or CT scan to confirm.

You’ll find posts here that dig into how D-dimer relates to other conditions, like how it’s used in COVID-19 patients to track clotting risk, or why it’s sometimes ordered after trauma or during pregnancy. You’ll also see how it fits into broader decisions—like when to start blood thinners, when to skip imaging, and how to avoid overtesting. This isn’t just about lab numbers. It’s about understanding when to act, when to wait, and how to make sense of a result that can mean everything or nothing.

Pulmonary Embolism: Sudden Shortness of Breath and How It's Diagnosed

Pulmonary Embolism: Sudden Shortness of Breath and How It's Diagnosed

  • Nov, 29 2025
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Sudden shortness of breath can be a sign of pulmonary embolism - a life-threatening blood clot in the lungs. Learn the key symptoms, how doctors diagnose it, and why early detection saves lives.

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