[Importance of laboratory investigations and trigger factors in chronic urticaria].

Urticaria is one of the most frequent skin disorders. Whereas for the acute form a cause is usually found, the aetiology of chronic urticaria often remains obscure. Infectious or autoimmune origin are presumed aetiologies, whereas trigger factors such as pressure, cold or food additives often induce an urticarial episode. In this study, we investigated the significance of laboratory and supplementary analysis in relation to the aetiology and classification of chronic urticaria. We also looked at a correlation of trigger factors with the aetiology and course of chronic urticaria. Out of 170 patients with chronic urticaria referred to our outpatient allergy clinic within 3 1/4 years, 95 were female (56%) and 75 male (44%). The average age was 37 years. Based on history and clinical signs, laboratory, allergo-immunological, stool and urine samples were performed, as well as allergological skin and physical tests. Of the laboratory parameters, total leukocyte count, C-reactive protein (CRP) and alanine-amino-transferase (ALAT) were the findings most often out of the normal range. In 25% (43/170) chronic urticaria could be attributed to a possible cause (infection [15%], autoimmunity [8%], allergy [1%], urticaria pigmentosa [1%]). Trigger factors were found in 84/170 (49%) patients (physical [29%], pseudoallergic [12%], combination of both [8%]). Follow-up after an average of 22.3 months revealed that 84 patients (63%) no longer suffered from urticarial disorders, while 49 (37%) still complained of hives. In conclusion, laboratory and supplementary investigations were rarely helpful in identifying aetiologic agents, although in 25% chronic urticaria was classified. Trigger factors are not of predictive value either for aetiology or course of chronic urticaria. However, the longer chronic urticaria lasts, the rarer are remissions. In younger patients, chronic urticaria tends to last less long than in elderly persons.