title: 13C-urea breath test for the diagnosis of Helicobacter pylori infection: are basal samples necessary?
abstract: OBJECTIVE
  The 13C-urea breath test (13C-UBT) is one of the best methods for the diagnosis of Helicobacter pylori infection. Basal breath samples are usually obtained, in addition to those obtained after urea intake, as it has been suggested that basal values may oscillate among a population (e.g. depending on diet). However, the superiority of this strategy has not been sufficiently demonstrated. The elimination of basal samples in the 13C-UBT protocol would have the advantages of higher simplicity and speed.
  
  
  METHODS
  The 13C-UBT was performed in 714 consecutive patients. Mean age was 48 +/- 16 years, 49% were males, and in 48% of the patients previous H. pylori eradication therapy had been administered. Basal samples (13C-basal) and at 30 min after taking 100 mg of urea labelled with 13C (13C-post-urea) were obtained, delta over baseline (13C-DOB) being the algebraic difference between the ratio 13C/12C at these two points (which is the parameter usually given in studies, being considered positive when > 5%). A citric acid solution was used prior to urea intake.
  
  
  RESULTS
  The prevalence of H. pylori infection was 48%. Mean values of 13C-basal, 13C-post-urea, and 13C-DOB were, respectively, -19 +/- 2, 5.9 +/- 33, and 25 +/- 33. 13C-basal values oscillated between -25 and -14, being between -21 and -16 in 90% of the cases. Linear correlation coefficient for 13C-post-urea and 13C-DOB was 0.999 (determination coefficient, 0.998; P< 0.0001). The area under the receiver operating characteristic (ROC) curve for the diagnosis of infection when only 13C-post-urea was used (taking 13C-DOB >5% as the 'gold standard') was 0.997. Best results were obtained with 13C-post-urea cut-off point set at -13, with sensitivity of 97.4% (95% CI, 95-99%), specificity of 99.5% (98-100%), and positive likelihood ratio of 180. The concordance kappa value for both tests (13C-post-urea and 13C-DOB) using the aforementioned cut-off point was 0.97.
  
  
  CONCLUSIONS
  When performing the 13C-urea breath test it is sufficient to obtain samples 30 min after urea intake. Basal breath samples would not be necessary, which further simplifies this diagnostic method.
authors: Department of Gastroenterology, Hospital de la Princesa, Universidad Autónoma de Madrid, Spain. gisbert@meditex.es
authors: J P
authors: JP
authors: Gisbert
authors: L M
authors: LM
authors: Benito
authors: S
authors: S
authors: Lara
authors: A
authors: A
authors: Vázquez
authors: I
authors: I
authors: Jiménez
authors: J M
authors: JM
authors: Pajares
mesh_terms: D000328:Adult; D001944:Breath Tests; D005260:Female; D016481:Helicobacter Infections / Q000175:diagnosis*; D016480:Helicobacter pylori; D006801:Humans; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D012044:Regression Analysis; D012189:Retrospective Studies; D014508:Urea / Q000378:metabolism*
chemical_list: D014508:Urea