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Kidney Week

Abstract: TH-PO391

Normalizing Urine Albumin to Urine Creatinine, Osmolality, or Not at All: Insights from NHANES

Session Information

Category: CKD (Non-Dialysis)

  • 2101 CKD (Non-Dialysis): Epidemiology, Risk Factors, and Prevention

Authors

  • Koopman, Jacob J. e., Leiden University Medical Center, Den Haag, Netherlands
  • Ix, Joachim H., UCSD, San Diego, California, United States
  • Scherzer, Rebecca, UCSF, San Francisco, California, United States
  • Shlipak, Michael, San Francisco VA Medical Center, San Francisco, California, United States
  • Waikar, Sushrut S., Harvard Medical School, Boston, Massachusetts, United States
Background

The concentration of urinary metabolites and proteins such as albumin is influenced by water excretion and urinary concentration, which varies across individuals and diurnally within individuals. To account for this variability, measures like albuminuria are often reported as normalized ratios. We hypothesized that the method of expressing urinary albumin – whether as a raw concentration or normalized to urine creatinine or osmolality – would influence observed associations with mortality due to confounding from determinants of urine creatinine excretion and osmolality, such as muscle mass, solute intake, and concentrating ability of the kidney.

Methods

We used data from the National Health and Nutrition Examination Survey 2009-2010 to model associations of albuminuria with mortality using Cox proportional hazards models. We used measurements on spot urine samples from 5,641 adults (age 42 + 17 yrs) who had follow-up information on vital status (377 deaths) over 6 years.

Results

Median estimated glomerular filtration rate was 97 (range, 7-170) ml/min/1.73m2, and median albumin:creatinine ratio was 5.9 (range 0.3-13,788) mg/g. The Table shows the associations of albuminuria with the risk of death. The strongest association was observed with urine albumin after multivariable adjustment for urinary creatinine.

Conclusion

While all methods of modeling urine albumin showed that elevated levels were independently associated with mortality, we found that associations were stronger when adjusted rather than normalized for urine creatinine and osmolality. Normalizing urinary biomarkers to urine creatinine may not be the optimal approach to distinguish urinary biomarker associations with health outcomes.

 Q1Q2Q3Q4
Urine albumin-1.78 (1.06-2.98)1.68 (1.12-2.51)2.12 (1.33-3.37)
Urine albumin:creatinine ratio-1.24 (0.74-2.07)1.62 (1.08-2.43)2.51 (1.60-3.92)
Urine albumin:osm ratio-0.82 (0.53-1.27)1.53 (0.94-2.50)1.85 (1.23-2.79)
Urine albumin, adjusted for urine creatinine-2.30 (1.33-3.99)2.42 (1.50-3.91)3.14 (1.86-5.30)
Urine albumin, adjusted for urine osm-2.10 (1.22-3.62)2.19 (1.34-3.56)2.80 (1.68-4.65)

Multivariable-adjusted (MV) hazard ratios (95% confidence intervals) for different measures of urinary albumin quartiles and the risk of death. Models were adjusted for age, sex, race/ethnicity, hypertension, cardiovascular disease, diabetes mellitus, body mass index, and estimated glomerular filtration rate.