title: Alveolar-arterial oxygen gradient in the assessment of acute pulmonary embolism.
abstract: OBJECTIVE
  The purpose of this investigation is to evaluate the utility of the alveolar-arterial (A-a) oxygen gradient in the diagnosis of acute pulmonary embolism (PE) among patients who participated in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIO-PED).
  
  
  METHODS
  Pulmonary embolism was diagnosed (n = 280) or excluded (n = 499) by angiography in all patients. Patients were then categorized as (1) the entire cohort, (2) no prior cardiopulmonary disease and no prior PE, and (3) no prior PE or deep venous thrombosis. Normal values of the A-a gradient were defined in three ways: (1) values < or = 20 mm Hg; (2) values < or = age/4 + 4; and (3) values based on age from the literature.
  
  
  RESULTS
  When a normal A-a gradient was defined as < or = 20 mmHg, 11 to 14% of patients with PE in the three categories of patients had a normal A-a gradient. When the equation age/4 + 4 was used, 8% to 10% of patients with PE in the three categories of patients had a normal A-a gradient. With age-related values from the literature, 20 to 23% of patients with PE in the three categories of patients had a normal A-a gradient. The A-a gradient was normal in comparable percentages of patients who did not have PE.
  
  
  CONCLUSIONS
  Normal values of the A-a gradient did not exclude the diagnosis of acute PE.
authors.affiliation: Henry Ford Heart and Vascular Institute, Detroit, Mich 48202-2691.
authors.forename: P D
authors.initials: PD
authors.lastname: Stein
authors.forename: S Z
authors.initials: SZ
authors.lastname: Goldhaber
authors.forename: J W
authors.initials: JW
authors.lastname: Henry
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000000981:diagnostic imaging; D011655:Pulmonary Embolism / Q000150:complications / Q000175:diagnosis* / Q000000981:diagnostic imaging; D011659:Pulmonary Gas Exchange; D011859:Radiography