Background: Injury to renal tubules plays an important role in the development of various renal diseases; however, the prevalence and significance of renal tubular damage in the general population are unclear. To clarify this point, we conducted a community-based study, using urinary β(2)-microglobulin as a marker of tubular damage.
Methods: The subjects studied were 3,444 Japanese over the age of 40 years. The urinary β(2)-microglobulin-creatinine ratio (UBCR) was assessed in morning spot urine samples.
Results: In this population, the distribution of the UBCR among these subjects was skewed towards higher values and a high UBCR (≥300 μg/g) was identified in 438 (12.7%) subjects. However, overlap with macroalbuminuria and renal insufficiency [estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2)] was observed in only 25 (5.7%) and 58 (13.2%) of these subjects, respectively. Multivariate analysis indicated that a high UBCR was positively associated with aging, hypertension, macroalbuminuria and increased urinary sodium excretion. A 5-year longitudinal analysis in 899 subjects indicated a greater decline in eGFR in parallel with the increase in baseline UBCR. After adjustment for possible confounders, a high UBCR was an independent risk factor for rapid decline in eGFR [<-10 mL/min/1.73 m(2); odds ratio 1.79 (95% confidence interval 1.07-2.99), P = 0.026].
Conclusion: This study showed that renal tubular damage was common and was an independent risk factor for renal deterioration in the Japanese population. More attention should be paid to occult renal tubular damage in order to prevent end-stage renal disease.