Measuring the albumin excretion rate: agreement between methods and biological variability

Area of Science:

• Nephrology
• Clinical Chemistry
• Diabetology

Background:

• Timed 24-hour urine collections for albumin excretion rate (AER) are cumbersome and prone to errors.
• Albumin excretion can be estimated using the albumin:creatinine ratio (ACR) in random urine samples.
• Previous studies focused on correlation, not agreement, and overlooked biological variability in AER.

Purpose of the Study:

• To determine the agreement between measured AER from 24-hour collections and estimated AER from ACR in random urine samples.
• To assess the impact of biological variability on AER measurements and estimations.
• To compare the reliability of ACR estimation versus timed collection for AER in diabetic patients.

Main Methods:

• Thirty diabetic patients with varying albuminuria and normal renal function provided two 24-hour and two random daytime urine specimens.
• AER was measured in 24-hour samples; AER was estimated from ACR in random samples multiplied by estimated creatinine excretion.
• Statistical analysis focused on limits of agreement for repeat measurements and estimates, and for averages of measurements and estimates.

Main Results:

• Wide limits of agreement were observed between repeat 24-hour AER measurements (33% to 490%).
• Estimated AER values from ACR were numerically similar to measured AER.
• Limits of agreement for ACR estimates did not significantly differ from measured AER, nor did comparisons of averaged values.

Conclusions:

• Albumin:creatinine ratio in random urine is a viable alternative to timed collections for estimating AER.
• The ACR method demonstrates comparable agreement to 24-hour collections, accounting for biological variability.
• This simplifies AER assessment in diabetic patients, enhancing clinical utility.