Method-to-method variability in urine albumin measurements.
BACKGROUND
Urine albumin (uALB) is a useful marker in diagnosis and treatment of renal microvascular disease. Beckman Coulter recently re-formulated their uALB reagent for the AU series of instruments to increase the analytical measurement range (AMR).


METHODS
Precision, linearity, reportable range, and analytical sensitivity for the reformulated reagent were determined using the AU680. In addition, the re-formulated AU reagent was compared to the previous generation AU reagent and to the Siemens Vista using residual urine specimens. The hook effect was evaluated on five instruments by spiking serum into albumin-free urine to generate a range of albumin concentrations.


RESULTS
Precision and linearity within the AMR were confirmed, along with accuracy of dilutions to extend the reportable range. For patient sample correlation, the re-formulated reagent demonstrated a positive 11% bias relative to the original AU reagent and a negative 11% bias relative to the Vista. Concentrations of uALB >3000mg/dL produced falsely low results for both AU reagents. The DCA Vantage assay "hooked" at even lower uALB concentrations.


CONCLUSIONS
The re-formulated AU uALB reagent met the manufacturer claimed performance characteristics. The AU and DCA Vantage were the only instruments of those tested affected by the hook effect in the concentration range evaluated. uALB assays are clearly not standardized, yet clinical guidelines dictate result interpretation. The method-to-method biases we observed here have the potential to lead to clinically significant post-analytical errors in uALB interpretation.
Department of Laboratory Medicine, University of Washington, Seattle, WA, United States.
Anna E
AE
Merrill
Department of Laboratory Medicine, University of Washington, Seattle, WA, United States.
Jenna
J
Khan
Seattle Children's Hospital, Seattle, WA, United States.
Jane A
JA
Dickerson
St. Paul's Hospital, Vancouver, BC, Canada; Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada.
Daniel T
DT
Holmes
Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL, United States.
Neil S
NS
Harris
Department of Laboratory Medicine, University of Washington, Seattle, WA, United States. Electronic address: dngreene@uw.edu.
Dina N
DN
Greene
D000418:Albumins / Q000032:analysis*; D000419:Albuminuria / Q000652:urine*; D006801:Humans; D007202:Indicators and Reagents / Q000592:standards; D015588:Observer Variation; D016482:Urinalysis / Q000295:instrumentation / Q000379:methods / Q000592:standards
D000418:Albumins; D007202:Indicators and Reagents
AU680; Hook effect; Method validation; Microalbumin; Standardization; Urine albumin