Impact of a negative D-dimer result on the initial assessment of acute aortic dissection. 
D-dimer shows high sensitivity but low specificity for the diagnosis of acute aortic dissection (AAD).  Previous reports indicated that negative D-dimer patients have shorter dissection length.  However, whether patients with negative D-dimer results have a good prognosis is unknown.  This study aimed to elucidate the clinical characteristics and implications of a negative D-dimer result on AAD diagnosis.  The study group comprised 126 patients (71 males, 55 females; mean age, 69 ± 11 years) with AAD admitted to our hospital between April 2009 and March 2015.  Blood samples on presentation were used for D-dimer measurement.  Clinical characteristics and outcomes were assessed.  Nine (7.1%) and 117 (92.9%) exhibited negative and positive D-dimer results, respectively.  The negative group showed a significantly lower extension score and a higher platelet count than the positive group.  Multivariate analysis demonstrated that platelet count (odds ratio, 1.31 (1.09-1.58), p = 0.003) and extension score (odds ratio, 0.56 (0.33-0.96), p = 0.03) were significantly related to a negative result.  Notably, 44% of patients in the negative group had type A dissection and 33% underwent an emergency operation due to cardiac tamponade.  We found that high platelet count and low extension score were independent factors related to a negative D-dimer result.  Even if the length of the dissection is short, an emergency operation is necessary in some patients with a negative D-dimer result.  Physicians should recognize that a negative D-dimer result alone cannot exclude patients with fatal AAD conditions.