There is limited ability to predict the severity of allergic reactions in children. Data derived predominantly from adults have implicated the platelet-activating factor pathway as a potential contributor to severe anaphylaxis. In this study, we sought to prospectively assess involvement of key components of the platelet-activating factor pathway in pediatric patients with anaphylaxis.
Forty-six pediatric patients (4 weeks after their acute presentation. These markers were compared to pediatric laboratory reference sera.
Severe anaphylaxis was experienced by 12/46 (26%) and mild-moderate anaphylaxis in 34/46 (74%) children. Platelet-activating factor acetylhydrolase (PAF-AH) activity was inversely associated with severe anaphylaxis: 9/12 children with severe anaphylaxis had reduced PAF-AH activity as compared to 14/34 with mild-moderate anaphylaxis (p<0.05). Furthermore, 3/3 children who required intensive care had markedly reduced mean PAF-AH (nmol/ml/min) (13.73, 95%CI:7.42-20.03) versus 20/23 who required ward/emergency department care (17.81, 95%CI:16.80-18.83; p<0.05). In children with anaphylaxis, PAF-AH during acute anaphylaxis was unchanged relative to the child's basal levels (mean, 17.26, 95%CI:16.10-18.42 vs 17.50, 95%CI:16.21-18.78, p=0.63) and was lower than healthy pediatric controls (mean 19.21; 95%CI:18.21-20.21; p<0.05).
Decreased serum PAF-AH activity is a biomarker of severe anaphylaxis. Levels of this enzyme do not change from basal levels during acute anaphylaxis. Our results show that PAF-AH is a biomarker of anaphylaxis severity in children. This key regulatory enzyme may modulate susceptibility to severe anaphylaxis.

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