Four cases of acute infectious urticaria showing significant elevation of plasma D‐dimer level

D‐dimer, a fibrinolytic end‐product, has been regarded as a biomarker indicating the severity of urticaria, especially in chronic urticaria. Regarding acute urticaria, D‐dimer level is also suggested to be elevated, which may be significant in comparison with chronic urticaria. However, the clinical features of acute urticaria with concomitant significant elevation of D‐dimer level have not been investigated in detail so far. We present four cases of acute urticaria fulfilling the proposed diagnostic criterion of acute infectious urticaria, in which significant elevation of D‐dimer level and rapid spontaneous normalization in parallel with the resolution of fever and urticaria occurs. No cases had deep vein thrombosis, disseminated intravascular coagulation and malignancy. All cases responded well to antihistaminic treatment in combination with antibiotics, and their fever and urticaria resolved within 10 days. All cases showed severe wheals persistent for several days resolving with hyperpigmentation. Histologically, infiltration into blood vessel walls and interstitial infiltration of lymphocytes and polymorphonuclear cells were marked in the dermis. In our cases, clinical features accorded with acute infectious urticaria, and their histological features were similar to those of neutrophilic urticaria as described previously. In conclusion, there is a certain group of acute urticaria associated with significant elevation of D‐dimer level. These common features of our cases may be characteristic in acute urticaria showing the coagulative and fibrinolytic abnormalities.