First-Void Urine Predicts Renal Events

The results suggest that clinicians should monitor kidney function by measuring the albumin/creatinine ratio from a first morning urine sample.

Screening for proteinuria may help identify people at risk for kidney disease progression, but uncertainties persist as to how urine should be collected and which specific urinary proteins should be measured. Because the different screening methods available may confuse clinicians, it may hamper the use of proteinuria to manage patients with kidney disease.

Hiddo Lambers Heerspink, PhD, University Medical Center Groningen, Groningen, The
Netherlands, and colleagues assessed and compared the ability of various proteinuria measures, including proteinuria versus albuminuria and 24-hours versus early morning sampling, to predict worsening kidney problems.

Four measures were compared:

• Urinary protein excretion from a 24-hour urine
• Urinary albumin excretion from a 24-hour urine collection;
  
• Urinary albumin concentration from a first morning urine sample; and
  
• Albumin:creatinine ratio from a first morning urine sample (the amount of albumin in the urine sample normalised by the amount of creatinine).
  

The investigators conducted their analysis in 701 patients with Type 2 diabetes and kidney disease who were participating in the Reduction in Endpoints in Non Insulin Dependent Diabetes Mellitus with the Angiotensin-II Antagonist Losartan (RENAAL) trial.

They defined worsening kidney function as the development of end-stage renal disease or a doubling of blood levels of creatinine.

Dr. Lambers Heerspink and his team found that measuring the albumin:creatinine ratio in a first morning urine sample was the superior method to predict kidney problems in patients with Type 2 diabetes and kidney disease.

"From a clinical point of view, these results are very important, because they imply that collection of first morning voids, which is clearly more convenient than collecting a 24-hour urine, can be used for assessment of proteinuria," said Dr. Lambers Heerspink. 

No previous study had examined the relative discriminatory capabilities of different proteinuria measures for predicting future renal events, the authors continued. To address the lack of data, Lambers Heerspink and colleagues reviewed data from the Reduction of Endpoints in Non Insulin Dependent Diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) trial (N Engl J Med 2001; 345: 861-869).

The authors noted that standardizing proteinuria measures will improve methods for detecting and monitoring kidney disease.

Practice Pearl:

The findings have potentially far-reaching implications for following diabetic patients with established nephropathy. The study showed that measuring albumin:creatinine ratio from a first-void urine sample is more accurate for predicting progression of kidney disease. 

Published online in the Journal of the American Society of Nephrology, July 2010

Lambers Heerspink HJ. et al "Comparison of different measures of urinary protein excretion for prediction of renal events" J Am Soc Nephrol 2010; DOI: 10.1681/ASN.2010010063.