Abstract
Albuminuria is a well known risk factor for cardiovascular disease and mortality, but focus on renal tubular dysfunction as a potential risk factor is growing also. The association between the urinary activity of N-acetyl-β-D-glucosaminidase (NAG) and cardiovascular risk has been assessed mostly in cross-sectional studies. We studied the cross-sectional associations between urinary NAG and cardiovascular risk factors and the longitudinal associations between NAG, cardiovascular disease, and all-cause mortality in a general population. Urinary NAG/creatinine ratio (NAG ratio) and albumin/creatinine ratio (ACR) were measured in 6834 participants of the Tromsø Study in 1994-1995. During the median 17.5 years of follow-up, 958 myocardial infarctions, 726 ischemic strokes, and 2358 deaths were registered. In multivariable analyses adjusted for albuminuria and cardiovascular risk factors, a baseline NAG ratio in the highest quartile was associated with an increased risk of myocardial infarction (hazard ratio [HR], 1.43; 95% confidence interval [95% CI], 1.16 to 1.76), ischemic stroke (HR, 1.41; 95% CI, 1.10 to 1.80), and all-cause mortality (HR, 1.60; 95% CI, 1.39 to 1.84). Combined, ACR and NAG ratio above median associated with a 48%-80% increased risk for the three end points. However, the NAG ratio did not add significantly to the baseline risk-prediction models when assessed by area under the receiver operating characteristics curve or net reclassification improvement. In conclusion, the nonsignificant improvement of risk prediction does not support the clinical use of NAG ratio in cardiovascular risk assessment in a low-risk group.