BACKGROUND: Urine albumin is the primary biomarker for detection and monitoring 
of kidney damage. Because fixed decision criteria are used to identify patients 
with increased values, we investigated if commonly used routine measurement 
procedures gave comparable results.
METHODS: Results from 17 commercially available urine albumin measurement 
procedures were investigated vs an isotope dilution mass spectrometry (IDMS) 
procedure. Nonfrozen aliquots of freshly collected urine from 332 patients with 
chronic kidney disease, diabetes, cardiovascular disease, and hypertension were 
distributed to manufacturers to perform urine albumin measurements according to 
the respective instructions for use for each procedure. Frozen aliquots were 
used for measurements by the IDMS procedure. An error model was used to 
determine imprecision and bias components.
RESULTS: Median differences between the largest positive and negative biases vs 
IDMS were 45%, 37%, and 42% in the concentration intervals of 12-30 mg/L, 31-200 
mg/L, and 201-1064 mg/L, respectively. Biases varied with concentration for most 
procedures and exceeded ± 10% over the concentration interval for 14 of 16 
quantitative procedures. Mean biases ranged from -35% to 34% at 15 mg/L. 
Dilution of samples with high concentrations introduced bias for 4 procedures. 
The combined CV was >10% for 5 procedures. It was not possible to estimate total 
error due to dependence of bias on concentration. CVs for sample-specific 
influences were 0% to 15.2%.
CONCLUSIONS: Bias was the dominant source of disagreement among routine 
measurement procedures. Consequently, standardization efforts will improve 
agreement among results. Variation of bias with concentration needs to be 
addressed by manufacturers.