Validation of a prediction rule for renal artery stenosis

Objectives We previously developed a prediction rule to estimate the probability of renal artery stenosis. This rule should be validated before it can be used reliably to select hypertensive patients for renal angiography. We determined the validity of the prediction rule in recent patients and in other settings. Design We studied three aspects of validity (agreement between predicted and observed probability of stenosis, discriminative ability, and clinical usefulness) in 180 consecutive patients with drug-resistant hypertension and normal or mildly impaired renal function, who visited six hypertension clinics of academic and community hospitals in the Netherlands. Thirty-five patients (19%) had a significant stenosis. Results The clinical characteristics in the rule (age, sex, vascular disease, recent onset of hypertension, smoking, body mass index, abdominal bruit, serum creatinine concentration, and hypercholesterolemia) had similar predictive value in the validation sample and development sample. The predicted probabilities of stenosis agreed well with the observed frequencies (Hosmer-Lemeshow goodness-of-fit test, P = 0.87). The prediction rule discriminated reasonably between patients with and without stenosis in the validation sample with an area under the receiver operating characteristic curve of 0.71. If only patients with predicted probabilities of stenosis of 5% or more were referred for renal angiography, the number of referrals was reduced by 20%, while 9% of patients with a stenosis were missed. Conclusions The prediction rule was valid in more recently treated patients in other settings. If used conservatively, the rule can reliably exclude a small proportion of patients from angiography.