Evaluation of urea reagent kits using the Centers for Disease Control and Prevention reference measurement procedures

"Open systems" are widely used for their low costs but may result in doubts in accuracy. Reference methods are encouraged to be established to work as standards to assess various kits on different systems.

The coupled-enzyme equilibrium method, recommended by the Centers for Disease Control and Prevention (CDC) as the urea reference method, was built up. Four urea kits, employed on the "open system" Beckman Coulter AU5400 analyzer, were compared with this reference method according to CLSI document EP9-A2.

The CVs of the coupled-enzyme equilibrium method at different urea levels ranged from 0.68% to 0.96% and its linear regression equation was Y = 1.0036X + 0.0169 (r = 0.9999, p < 0.01). Its average recovery was 101.30% and the results of the External Quality Assessment Scheme for Reference Laboratories in Laboratory Medicine (RELA) were within acceptable limits. Four evaluated urea kits were closely correlated with the reference method (r > 0.999). Beckman Coulter and Roche kits showed a slightly negative bias (mean ± 2SD: -0.02 ± 0.36 mmol/L and -0.01 ± 0.31 mmol/L); Ausbio kits showed a small negative bias (mean ± 2SD: -0.06 ± 0.34 mmol/ L). The KHB kits showed a small positive bias (mean ± 2SD: 0.04 ± 0.31 mmol/L).

Four urea kits used on a Beckman Coulter analyzer showed good correlations with the urea reference method. Therefore, by comparison with reference methods, "open systems" may maintain low costs without compromising accuracy.