Elevated Blood Urea Nitrogen is Associated With Critical Limb Ischemia in Peripheral Arterial Disease Patients

As renal function is often impaired in atherosclerosis patients, accelerating atherosclerosis per se and creating a vicious cycle, we investigated the association of blood urea nitrogen (BUN) and critical limb ischemia (CLI) in peripheral arterial occlusive disease (PAOD) patients. Our cross-sectional study included 1521 PAOD patients, with normal and impaired renal function treated at our institution from 2005 to 2010. Patients on renal replacement therapy were excluded. The cohort was divided into tertiles according to the serum BUN levels. An optimal cutoff value for the continuous BUN was calculated by applying a receiver-operating curve analysis to discriminate between CLI and non-CLI. In our cohort, CLI increased significantly with an increase in BUN (13.1% in the first tertile, 18.7% in the second tertile, 29.0% in the third tertile, P for trend < 0.001). A BUN of 17.7  mg/dL was identified as an optimal cutoff. Accordingly, there were 2 groups of patients: 636 patients with BUN ≤ 17.7 and 885 patients with BUN > 17.7. CLI was more frequent in BUN > 17.7 patients (342 [38.6%]) than in BUN  ≤ 17.7 patients (134 [21.1%]) (P < 0.001); the same applied to prior myocardial infarction (45 [5.1%] vs 15 [2.4%], P = 0.007) and congestive heart failure (86 [9.7%] vs 31 [4.9%], P < 0.001). A BUN > 17.7 was associated with an odds ratio of 1.6 (95% confidence interval: 1.3-1.9, P < 0.001) for CLI even after the adjustment for other established vascular risk factors such as age ≥ 75 and type 2 diabetes. An increased BUN is significantly associated with a high risk for CLI and other vascular endpoints. The BUN is an easily determinable, broadly available, and inexpensive marker that could be used to identify patients at high risk for vascular endpoints.