Background: The National External Quality Assessment Service on urinalysis in Korea has used control materials manufactured by YD (YD Diagnostics, Korea). These materials are composed of phosphate-buffered saline mixed with real materials or chemical reagents. Therefore, matrix effects could influence the urine analysis results.
Methods: We obtained five kinds of control materials from YD Diagnostics, Aution Check Plus (Arkray Inc., Japan), Liquichek Urinalysis Control (Bio-Rad Inc., USA), UroColor Control (Standard Diagnostics, Korea), and UC-Control (Sysmex Co., Japan), and prepared normal and abnormal human urine samples for testing. As test devices, we selected the following six instruments: Super+ (YD Diagnostics), Aution Max AX-4030 (Arkray Inc.), UroMeter 720 Pro (Standard Diagnostics), Clinitek Adventus (Siemens Healthcare, Germany), URISYS 2400 (Roche Diagnostics, Germany), and UC1000 (Sysmex Co.) based on the database of the Korean Association of External Quality Assessment Service. We performed our analysis using the five control materials, two human urine samples, and six instruments.
Results: Matrix effects were found in all control materials: Aution Check (pH in URISYS, specific gravity [SG] in Aution Max), Liquichek (urobilinogen in Aution Max, SG in UC1000), UroColor (bilirubin and SG in Aution Max, pH and SG in UC1000), and UC-Control (bilirubin and SG in UroMeter, bilirubin in UC1000, and ketone in Clinitek). YD controls also presented matrix effects: blood and urobilinogen in Aution Max, glucose in Super+, SG in UC1000, and pH in URISYS.
Conclusions: Since all control materials showed matrix effects, external quality assessment should be evaluated by the results of the peer group rather than by those of the manufacturer.

Keywords: Urine, Quality control, Urinalysis