Kidney function, albuminuria and life expectancy

BACKGROUND Lower estimated glomerular filtration rate is associated with reduced life expectancy. Whether this association is modified by the presence or absence of albuminuria, another cardinal finding of chronic kidney disease, is unknown. OBJECTIVE Our objective was to estimate the life expectancy of middle-aged men and women with varying levels of eGFR and concomitant albuminuria. DESIGN A retrospective cohort study. SETTING A large population-based cohort identified from the provincial laboratory registry in Alberta, Canada. PARTICIPANTS Adults aged ≥30 years who had outpatient measures of serum creatinine and albuminuria between May 1, 2002 and March 31, 2008. MEASUREMENTS PREDICTOR Baseline levels of kidney function identified from serum creatinine and albuminuria measurements. OUTCOMES all cause mortality during the follow-up. METHODS Patients were categorized based on their estimated glomerular filtration rate (eGFR) (≥60, 45-59, 30-44, and 15-29 mL/min/1 · 73 m(2)) as well as albuminuria (normal, mild, and heavy) measured by albumin-to-creatinine ratio or urine dipstick. The abridged life table method was applied to calculate the life expectancies of men and women from age 40 to 80 years across combined eGFR and albuminuria categories. We also categorized participants by severity of kidney disease (low risk, moderately increased risk, high risk, and very high risk) using the combination of eGFR and albuminuria levels. RESULTS Among men aged 50 years and with eGFR ≥60 mL/min/1.73 m(2), estimated life expectancy was 24.8 (95% CI: 24.6-25.0), 17.5 (95% CI: 17.1-17.9), and 13.5 (95% CI: 12.6-14.3) years for participants with normal, mild and heavy albuminuria respectively. Life expectancy for men with mild and heavy albuminuria was 7.3 (95% CI: 6.9-7.8) and 11.3 (95% CI: 10.5-12.2) years shorter than men with normal proteinuria, respectively. A reduction in life expectancy was associated with an increasing severity of kidney disease; 24.8 years for low risk (95% CI: 24.6-25.0), 19.1 years for moderately increased risk (95% CI: 18.7-19.5), 14.2 years for high risk (95% CI: 13.5-15.0), and 9.6 years for very high risk (95% CI: 8.4-10.8). Among women of similar age and kidney function, estimated life expectancy was 28.9 (95% CI: 28.7-29.1), 19.8 (95% CI: 19.2-20.3), and 14.8 (95% CI: 13.5-16.0) years for participants with normal, mild and heavy albuminuria respectively. Life expectancy for women with mild and heavy albuminuria was 9.1 (95% CI: 8.5-9.7) and 14.2 (95% CI: 12.9-15.4) years shorter than the women with normal proteinuria, respectively. For women also a graded reduction in life expectancy was observed across the increasing severity of kidney disease; 28.9 years for low risk (95% CI: 28.7-29.1), 22.5 years for moderately increased risk (95% CI: 22.0-22.9), 16.5 years for high risk (95% CI: 15.4-17.5), and 9.2 years for very high risk (95% CI: 7.8-10.7). LIMITATIONS Possible misclassification of long-term kidney function categories cannot be eliminated. Possibility of confounding due to concomitant comorbidities cannot be ruled out. CONCLUSION The presence and degree of albuminuria was associated with lower estimated life expectancy for both gender and was especially notable in those with eGFR ≥30 mL/min/1.73 m(2). Life expectancy associated with a given level of eGFR differs substantially based on the presence and severity of albuminuria.