title: Urinary leukotriene E₄ levels identify children with tobacco smoke exposure at risk for asthma exacerbation.
abstract: BACKGROUND
  Children with asthma exposed to secondhand smoke (SHS) might be at higher risk for severe exacerbations, but biomarkers of susceptibility to SHS exposure have not been previously reported.
  
  
  OBJECTIVE
  We sought to assess the usefulness of urinary leukotriene E(4) (uLTE₄) levels in the prediction of increased risk of severe asthma exacerbations requiring emergency department (ED) or urgent care (UC) visits.
  
  
  METHODS
  Forty-four schoolchildren with moderate-to-severe asthma receiving inhaled corticosteroids were followed for 5 months with repeated measurements of uLTE₄ and monitoring of ED and UC visits. SHS exposure status was determined by using prestudy questionnaires and repeated measurements of urinary cotinine during the study.
  
  
  RESULTS
  Nine (45%) of 20 children with SHS exposure experienced a severe exacerbation requiring an ED or UC visit compared with 3 (12.5%) of 24 children without significant SHS exposure (relative risk, 3.6; 95% CI, 1.1-11.5; P = .02). The uLTE₄ level was a significant predictor of exacerbation risk in children exposed to SHS (area under the curve, 0.85; P = .003). Other predictors, such as nighttime symptom frequency, prebronchodilator and postbronchodilator lung function, and exhaled nitric oxide levels, were not related to exacerbations in this group. uLTE₄ levels at or greater than 106 pg/mg achieved 67% (6/9) sensitivity and 100% (11/11) specificity for predicting children with SHS exposure who required an ED or UC visit.
  
  
  CONCLUSIONS
  Children exposed to SHS are at increased risk for severe asthma exacerbations, despite use of inhaled corticosteroids. uLTE₄ levels identify children exposed to SHS at high risk for asthma exacerbations.
authors.affiliation: Department of Pediatrics, National Jewish Health, Denver, CO 80206, USA. rabinovitchn@njhealth.org
authors.forename: Nathan
authors.initials: N
authors.lastname: Rabinovitch
authors.forename: Nichole
authors.initials: N
authors.lastname: Reisdorph
authors.forename: Lori
authors.initials: L
authors.lastname: Silveira
authors.forename: Erwin W
authors.initials: EW
authors.lastname: Gelfand
mesh_terms: D000280:Administration, Inhalation; D000293:Adolescent; D001249:Asthma / Q000139:chemically induced* / Q000188:drug therapy / Q000503:physiopathology*; D015415:Biomarkers / Q000652:urine*; D002648:Child; D005260:Female; D006801:Humans; D017999:Leukotriene E4 / Q000652:urine*; D008297:Male; D011237:Predictive Value of Tests; D012306:Risk; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014028:Tobacco Smoke Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data
chemical_list: D015415:Biomarkers; D014028:Tobacco Smoke Pollution; D017999:Leukotriene E4