title: State of the art for measurement of urine albumin: comparison of routine measurement procedures to isotope dilution tandem mass spectrometry.
abstract: 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.
authors.affiliation: Department of Pathology, Virginia Commonwealth University, Richmond, VA;
authors.forename: Lorin M
authors.initials: LM
authors.lastname: Bachmann
authors.forename: Goran
authors.initials: G
authors.lastname: Nilsson
authors.forename: David E
authors.initials: DE
authors.lastname: Bruns
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McQueen
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
authors.forename: Jack J
authors.initials: JJ
authors.lastname: Zakowski
authors.forename: W Greg
authors.initials: WG
authors.lastname: Miller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D007201:Indicator Dilution Techniques; D008875:Middle Aged; D009842:Oligopeptides / Q000032:analysis; D012709:Serum Albumin / Q000032:analysis* / Q000737:chemistry; D053719:Tandem Mass Spectrometry / Q000379:methods; D016482:Urinalysis / Q000379:methods / Q000592:standards; D055815:Young Adult
chemical_list: D009842:Oligopeptides; D012709:Serum Albumin