Method-to-method variability in urine albumin measurements.

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Diagnostic Assays

Background:

• Urine albumin (uALB) is a critical biomarker for diagnosing and managing renal microvascular disease.
• Beckman Coulter updated their uALB reagent for AU instruments to expand the analytical measurement range (AMR).

Purpose of the Study:

• To evaluate the performance of the reformulated Beckman Coulter AU urine albumin reagent.
• To compare the reformulated reagent against the previous AU reagent and the Siemens Vista assay.
• To assess the hook effect in urine albumin assays across multiple instruments.

Main Methods:

• Assessed precision, linearity, reportable range, and analytical sensitivity of the reformulated reagent on an AU680.
• Compared the reformulated AU reagent with the prior AU reagent and Siemens Vista using residual urine.
• Evaluated the hook effect by spiking serum into albumin-free urine across five instruments.

Main Results:

• The reformulated reagent demonstrated acceptable precision and linearity within its AMR.
• Method comparison showed an 11% positive bias versus the original AU reagent and an 11% negative bias versus the Siemens Vista.
• Falsely low urine albumin results occurred at concentrations above 3000 mg/dL for both AU reagents; the DCA Vantage assay exhibited hook effect at lower concentrations.

Conclusions:

• The reformulated AU uALB reagent meets manufacturer specifications.
• The AU and DCA Vantage assays were susceptible to the hook effect within the tested concentration range.
• Significant method-to-method biases in urine albumin assays can lead to clinically relevant post-analytical errors, highlighting a lack of standardization.