D-dimer is a degradation product of cross-linked fibrin formed during activation of the coagulation system. It is commonly used to diagnose thromboembolic disease in outpatients suspected of having deep venous thrombosis (DVT) and pulmonary embolism (PE). By providing a quick, non-invasive alternative to costly imaging, D-dimer has demonstrated to aid in the detection of venous thromboembolism (VTE) in outpatients. In normal dogs and cats, D-dimer in serum is less than 300 ng/ml, which is to be cut-off value of the diagnostic kit.