title: Likelihood ratios in the diagnosis of renal artery stenosis by magnetic resonance angiography compared with renal angiography.
abstract: BACKGROUND
  Renal angiography (RA) is considered to be the gold standard for the diagnosis of renal artery stenosis (RAS). However, it is invasive and potentially harmful; hence there is a need for an optimal noninvasive test. Magnetic resonance angiography (MRA) is currently accepted as the optimal noninvasive test by many. However, its major drawback is its inability to grade quantitatively the degree of stenosis. In this study, likelihood ratios (LR) were used to compare the diagnostic accuracy of MRA with that of RA.
  
  
  METHODS
  To test the hypothesis that semiquantitatively graded MRA would correlate with RA, a retrospective analysis was performed to determine the LR of MRA to diagnose RAS compared with RA. It was believed that LR > or = 10.0 or < or =0.1 might generate conclusive changes from pretest to post-test probabilities. In this study a total of 94 renal arteries from 48 patients were analyzed for RAS by MRA and RA. Stenoses were graded by MRA as mild (<50%), moderate (50% to 75%), or severe (>75%); and by RA as <75% or > or =75% stenosis.
  
  
  RESULTS
  The LR was 0.13 (95% CI = 0.09 to 0.19) for mild stenosis, 0.11 (95% CI = 0.08 to 0.15) for moderate stenosis, and 2.2 (95% CI = 1.9 to 3.1) for severe stenosis by MRA.
  
  
  CONCLUSIONS
  Nonsevere stenosis can be sufficiently diagnosed by MRA and may not warrant RA. However, it may be insufficiently precise to establish severe RAS based on LR results. Therefore, for severe RAS by MRA, the decision to obtain RA can be made with the help of post-test probability, which is determined using pretest probability and LR.
authors.affiliation: Division of Nephrology and Hypertension, Department of Medicine, Henry Ford Hospital, Detroit, Michigan 48202, USA. nattall1@hfhs.org
authors.forename: Nizar
authors.initials: N
authors.lastname: Attallah
authors.forename: Jerry
authors.initials: J
authors.lastname: Yee
authors.forename: Adrienne
authors.initials: A
authors.lastname: Gutierrez
authors.forename: Joseph
authors.initials: J
authors.lastname: Musial
authors.forename: Raviprasenna
authors.initials: R
authors.lastname: Parasuraman
mesh_terms: D000328:Adult; D000368:Aged; D000792:Angiography / Q000379:methods* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D018810:Magnetic Resonance Angiography / Q000379:methods / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012078:Renal Artery Obstruction / Q000175:diagnosis* / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D012720:Severity of Illness Index