Evaluating the analytical quality control of urinary albumin measurements using sigma metrics.

BACKGROUND

There is no worldwide recognized reference system and standard for urinary albumin measurement until now, so the analytical quality from different laboratories has always varied. In this study, we aimed to evaluate the analytical performance of a urinary albumin assay system using Sigma-metric, and thereby choose a suitable control rule to guarantee the analytical quality of the assays.

METHOD

Two levels of diluted reference material (ERM-DA47OK/IFCC) were used to calculate the biases, the coefficient of variation (CV) were calculated from six months of internal quality control measurements at two levels, and the external quality assessment standard of China for urinary albumin (30%) was used as the total allowable error(TEa).

RESULTS

The Sigma values for quality control levels 1 and 2 were 4.28 and 6.14, leading to recommended Westgard rules of 1/2/R/4 (N = 2, R = 2) and 1(N = 2, R = 1), respectively. Westgard rule 1/2/R/4(N = 2, R = 2) was selected for the quality control of the urinary albumin measurements, and with it, the power function graph showed a high efficacy for determining the detection errors with a probability of false rejection of 1.004% and a probability of error detection of 98.80%.

CONCLUSION

With a TEa of 30% recommended by the external quality assessment standard of China, Westgard rule 1/2/R/4(N = 2, R = 2) with a high efficacy for determining the detection error is recommended for the quality control of urinary albumin measurements.