A normal D-dimer does not rule out pulmonary embolism. An elevated D-dimer suggests the possibility of pulmonary embolism, but is not specific, as there are many other diseases that can cause an elevated D-dimer. Also, elevated D-dimer alone cannot confirm the diagnosis of pulmonary embolism, so a normal D-dimer cannot exclude pulmonary embolism, and in the case of a small embolus embolizing a branch of the pulmonary artery, the D-dimer may not be elevated at all. The real test to confirm and exclude pulmonary embolism is pulmonary arteriography, which is the gold standard of examination and is invasive (invasive test), complicated and expensive, and requires high technical skills of the operator. CT reconstruction of the pulmonary arteries is also very accurate and can confirm or exclude pulmonary embolism in most cases, but it is also very expensive and simpler to perform than pulmonary angiography.