Evaluation of a urinary metanephrines reagent kit: an automated approach

We report the results of a laboratory evaluation of the BioRad Urinary Metanephrines Reagent Kit. The test was designed for the quantitative measurement of normetanephrine and metanephrine in urine by high performance liquid chromatography. The kit was evaluated in view of improving assay reliability and specificity as compared to the manual method based on cation exchange chromatography and spectrophotometry.

Performance was evaluated for precision, linearity, accuracy, sensitivity and detection limit based on National Committee on Clinical Laboratory Standards (NCCLS) protocols. Analytical precision was evaluated using commercial controls and patient sample. Accuracy was evaluated by assessing recovery. Linearity was determined using aqueous standards.

The within-run coefficient of variation (CV) for metanephrine and normetanephrine were 1.9 percent and 2.4 percent (low control); 4.2 percent and 3.5 percent (high control); 3.8 percent and 3.3 percent (patient sample), respectively. The between-day precisions were 3.8 percent and 4.3 percent (low control); and 5.5 percent and 3.7 percent (high control) for metanephrine and normetanephrine, respectively. The linearity curve showed metanephrine and normetanephrine to be linear with concentrations, to at least 1,600 microgramme per litre and 2,000 microgramme per litre, respectively. Analytical recovery averaged 102 percent for metanephrine and 95 percent for normetanephrine. Levels as low as 23 microgramme per litre normetanephrine and 10 microgramme per litre metanephrine were measured with this method. The detection limit was 3.3 microgramme per litre for metanephrine.

The performance characteristics of automated sample preparation and auto-injection facilitate handling of larger number of samples as well as improve assay reliability.