Are triplicate urine samples necessary to assess albuminuria?

BACKGROUND/AIMS: Urinary albumin excretion is subject to intra-individual variability. Thus, for research purposes, it is recommended to test three urine samples collected over a short period of time. The objective of our analysis was to check the usefulness of triplicate samples to determine the albuminuric status of diabetic patients.

METHODS

We present the results of the non-planned retrospective analysis of 246 triplicate morning urine samples obtained from 95 type 2 diabetics included in three multinational, randomized, double-blind studies. Albuminuria was determined by immunoturbidimetry on fresh samples in the same central laboratory. Microalbuminuria was defined by a urine albumin to creatinine ratio (UACR) between 2.5 and 25 mg/mmol in males and between 3.5 and 35 mg/mmol in females. Concordance was obtained when the second and/or third sample (UACR2 and UACR3) confirmed the albuminuric status obtained from the first sample (UACR1).

RESULTS

Considering the first samples, 9% were within the normal range, 35% showed microalbuminuria and 56% showed macroalbuminuria. The overall concordance rate was 95%. The log of UACR was highly correlated between samples. Bland-Altman plots expressed in percent variations between two samples confirmed that the mean variation was low (around 8%) but revealed the scattering of values, 95% being between -60 and +77% of variation between samples.

CONCLUSIONS

There is no benefit in repeating morning UACR determination in diabetic patients to accurately categorize a subject as having normo-, micro- or macroalbuminuria. However, in order to accurately quantify albuminuria, repeated determinations are required.