Laboratory evaluation of the COBAS MIRA S random access analyser

The random access analyser COBAS MIRA S (Roche Diagnostics) was evaluated for two months. The instrument is a computer-controlled discrete analyser which can be run in a combination profile and single test mode. This instrument has special features, including an automatic cuvette segment changer, a reagent rack cooling system, an external keyboard and monitor, as well as a bar-code facility for the entry of test parameters, worklists and sample identification numbers. Study of within-run and between-run precision gave values of % CV 0.54-3.37 and 0.61-3.65, respectively, for a variety of assays. Linearity testing to the upper limit of each test was also studied and were found to cover the necessary pathological range. Within the two-month period, no major problems were encountered. The instrument required minimum operator attention during operation. Correlation studies with the Hitachi 705 using six clinical chemistry tests (glucose, cholesterol, triglyceride, ALP, AST, ALT) gave correlation coefficients ranging from 0.95-0.99 and slopes of 0.91-1.17.

performed. The evaluation studies performed included within-run and between-run precision at four analyte concentrations, method linearity and relative accuracy (comparison studies).
The random access analyser COBAS MIRA S (Roche Diagnostics) was evaluated for two months. The instrument is a computer-controlled discrete analyser which can be run in a combination profile and single test mode. This instrument has specialfeatures, including an automatic cuvette segment changer, a reagent rack cooling system, an external keyboard and monitor, as well as a bar-codefacility for the entry of testparameters, worklists and sample identification numbers. Study of within-run and between-run precision gave values of% CV 0"54-3"37 and 0"61-3"65, respectively, for a variety of assays. Linearity testing to the upper limit of each test was also studied and were found to cover the necessary pathological range. Within the two-month period, no major problems were encountered. The instrument required minimum operator attention during operation. Correlation studies with the Hitachi 705 using six clinical chemistry tests (glucose, cholesterol, triglyceride, ALP, AST, ALT) gave correlation coefficients ranging from 0"95-0"99 and slopes of 0"91-1.17. advantages with regard to flexibility, immediate readiness and reliability [1,2]. The random access analyser COBAS MIRA S is an extended version of the wellknown COBAS MIRA [3]. This (MIRA S) analyser has an automatic cuvette segment changer, a cooled reagent compartment and improved system software. The filterphotometer system can be monitored in parallel at five different wavelengths: 340, 405, 500, 550 and 600 nm.
The working temperature 30 C is sustained by an air bath and monitored by a thermistor located within the chamber. The software permits the determination of routine clinical chemical analytes by using theoretical calculation factors, calibrators or standard dilution curves. Predilutions of standards and/or samples can be programmed easily. The test results of the determinations are automatically transferred to the 'patient report'. Each patient's data can be recalled and printed whenever needed.
In this paper, the results of an assessment on the analytical performance of COBAS MIRA S are reported. Six routine chemistry tests were selected (table 1) for use in the study of its suitability and usefulness in smallto medium-sized laboratories where routine service and stat

Instruments
The COBAS MIRA S was on loan from Roche Diagnostics, Switzerland. All necessary reagents (UNI-KIT) and calibrators were also supplied by Roche. The methods employed for the six analytes, the amount of sample volumes and total reagent volumes are shown in    More than 120 patient samples (low, normal and abovenormal levels) were selected for comparison studies. Half of each specimen was used for assays in the COBAS MIRA S, while the other half was used for assays in the Hitachi 705. The above-normal concentration specimens were used in the linearity studies.

Calibration
The COBAS MIRA S and the Hitachi 705 were calibrated with Roche Diagnostics calibration material.

Precision
The evaluation of the performance of COBAS MIRA S took two months. Close supervision and appropriate training were given initially by Roche Diagnostics (Thailand) Ltd. Within-run and between-run precisions were assessed. Six clinical chemical analytes were selected; glucose, cholesterol, triglyceride, alkaline phosphatese (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT). For within-run studies, four commercially available control sera were analysed 20 times each in single batches, while the between-run

Discussion
The purpose of this study was to assess the overall performance of the COBAS MIRA S in a clinical laboratory performing routine tests.
The precision data in table 3 and 4 show that the range of precision determined from COBAS MIRA S is within the acceptable limits. The good precision with % CV, in the range of 0"5-3"6, may be due to the pipetting system, where the reagent and sample probe are washed, and to the individual reaction cuvette used in the test measurement.
The comparison of the test results obtained on serum samples with COBAS MIRA S and with the Hitachi 705 shows that the degree of correlation was very good (r ranging from 0"95-0"99).
In laboratories where ambient controlled temperature is often in the range of 25-30 C, the rack cooling device is a very useful compartment to hold temperature-sensitive reagents, especially where large batch of reagents are needed to facilitate the 'true walk-away' facility (provided by the manufacturers for 312 analyses to be determined in one run and facilitated by the automatic cuvette segment changer).
The instrument performed well over the evaluation period. No major problems with regards to instrument failure occurred during the study. The operator's manual and guidelines for trouble-shooting were easy to follow.
In conclusion, the COBAS MIRA S is a flexible, convenient and easy-to-use analyser for either batch or random access work. Its design and operational simplicity provides reliable analytical data, as demonstrated by good correlation with the existing instrument. Unique, cooled reagent reservoirs and sealed serum cups make the COBAS MIRA S an ideal instrument for use in small to medium-sized laboratories where efficient output of laboratory data is required.