Histamine and tryptase levels in patients with acute allergic reactions: An emergency department-based study

Background: Emergency department visits for acute allergic reactions are co mmon. Although the diagnosis and classification of these allergic reactions is primarily empiric, it is not always clear whether certain signs and sym ptoms constitute systemic mediator release syndromes, such as anaphylaxis, and thus may warrant more aggressive therapy or follow-up. Objective: We sought to determine associations between various clinical sig ns and symptoms with both plasma histamine levels and serum tryptase levels in adult patients presenting to an emergency department with acute allergi c syndromes. The clinical correlates of raised beta-tryptase levels were al so investigated. Methods: Ninety-seven adult emergency department patients were prospectively studied by using a questionnaire, physical examination, and serum-plasma sampling. Plasma histamine and serum total and beta-trypta se levels were determined. Clinical groupings were compared for mediator le vels by using simple and multivariate analysis. Results: Elevated levels of plasma histamine (>10 nmol/L) and serum total t ryptase (>15 ng/mL) were observed in 42 and 20 patients, respectively. Dete ctable P-tryptase (greater than or equal to 1 ng/mL) was observed in 23 pat ients, including 15 of the patients with elevated total tryptase levels. Su spected food allergy incidences and the duration of reaction were similar i n patients with increased histamine levels and in patients with increased t ryptase levels. Increased total tryptase levels, histamine Levels, or both were observed in some patients who did not have airway, cardiovascular, or abdominal signs. Histamine levels correlated better with clinical signs tha n tryptase levels. Histamine elevations (>10 nmol/L) were observed more fre quently in patients characterized by the following clinical signs in univar iate analysis: the presence of urticaria, more extensive erythema, abnormal abdominal findings, and wheezing. Total tryptase increases were observed m ore Frequently only in patients with urticaria. Histamine levels correlated with initial heart rates. In multivariate analysis the extent of urticaria was the best single predictor of plasma histamine levels and of either an elevated histamine or tryptase Level. Detectable beta-tryptase levels were observed in some patients who had neither elevated total tryptase nor eleva ted histamine levels. Unlike patients without detectable beta-tryptase leve ls, patients who had detectable beta-tryptase levels had a significant corr elation between total tryptase and histamine levels (P < .05). Conclusions: Raised histamine and, less commonly, raised tryptase levels ar e observed in almost 50% of patients presenting to emergency departments wi th acute allergic reactions. Some cases associated with systemic mediator r elease do not have classical features of severe anaphylaxis, such as hypote nsion or tachycardia. The lack of total tryptase elevations in many patient s with elevated plasma histamine levels suggests basophil involvement. The clinical utility of beta-tryptase determinations in the evaluation of acute allergic reactions needs further study.