Evaluation of the Technicon Axon analyser

An evaluation of the Technicon Axon analyser was carried out following the guidelines of the ‘Sociedad Española de Química Clínica’ and the European Committee for Clinical Laboratory Standards. A photometric study revealed acceptable results at both 340 nm and 404 nm. Inaccuracy and imprecision were lower at 404 nm than at 340 nm, although poor dispersion was found at both wavelengths, even at low absorbances. Drift was negligible, the imprecision of the sample pipette delivery system was greater for small sample volumes, the reagent pipette delivery system imprecision was acceptable and the sample diluting system study showed good precision and accuracy. Twelve analytes were studied for evaluation of the analyser under routine working conditions. Satisfactory results were obtained for within-run imprecision, while coefficients of variation for betweenrun imprecision were much greater than expected. Neither specimenrelated nor specimen-independent contamination was found in the carry-over study. For all analytes assayed, when comparing patient sample results with those obtained in a Hitachi 737 analyser, acceptable relative inaccuracy was observed.


Introduction
The Technicon Axon TM system (Technicon Instruments Corporation, Tarrytown, New York 10591-5097, USA) is a random access biochemistry analyser, which can perform both spectrophotometric and ISE tests. The instrument was evaluated according to the protocol of the 'Sociedad Espafiola de Qufmica Clfnica' (SEQC) [1,2] and the European Committee for Clinical Laboratory Standards (ECCLS) [3]. The evaluation of the analytical units included studies of inaccuracy, imprecision, linearity and drift of the spectrophotometer; imprecision and inaccuracy of the pipette delivery systems (sample and reagents) and of the dilution system; within-run and between-run analytical imprecision, specimen-related and specimen-independent carry-over and relative inaccuracy compared to the results obtained with a Hitachi 737 analyser.
The workstation allows easy management of the analyser. Features of the workstation include: demographic entry for 972 patients and samples per day; daily and cumulative Westgard quality control; bidirectional host computer communication; over 2000 reaction curves in memory which can be requested at any time; and the ability to visualize reaction curves in real time.
The analytical system contains the hardware and software necessary to perform each analysis (sample tray and reagent trays, reaction cuvettes, spectrophotometer etc.). The reagent system consists of two trays (2 x 27 reagents with only six positions for user-defined chemistries) and is provided with two syringes (a 1000 txl syringe for aspirating diluent/rinse water and a 500 tl syringe for aspirating/dispensing reagent). Each reagent system, R1 and R2, has its own probe. The first reagent is delivered into the reaction cuvette 37"5 s after the addition of sample. R2 addition time is fixed at 4 min after the addition of R1 to the reaction cuvette. Each reagent tray is divided in two partitions: 21 compartments are kept at between 6 C and 10 C, and six compartments are kept at room temperature. The maximum reagent volume is fixed at 400 1. Up to 38 tests per sample can be requested (36 colorimetric and two ISE).
The delivery of sample into the reaction cuvette is achieved by a process similar to that of reagent delivery.
It also consists of two syringes (a 50 1 syringe for aspirating sample and a 500 1 syringe for aspirating sample diluent/rinse water and for dispensing sample and diluent through the probe). Within the sample probe, air is used to separate the sample and rinse water, and also to prevent splashing at the tip when dispensing sample. Sample v!alnes range from 3 to 47 tl. Up to nine aspirations can be achieved per cup. Up to five automatic dilutions of the sample can be performed. The dilution system allows the operator to use the same chemistries for blood and urine analysis.
The reaction tray contains 90 re-usable, washable, 6 mm light-path Pyrex glass cuvettes. The wash station contains 11 positions, which alternately wash and rinse cuvettes before drying. The sample and reagent probes have their own wash stations where the rinse syringe dispenses a fixed amount of degassed water through the respective probe.

Instrument
The Technicon Axon is a dual module analyser consisting of the analyser itself and a data processor (workstation).
The following types of analysis can be carried out: zeroorder and first-order rate, endpoint and blank-corrected (rate and endpoint) analysis.   (2) Sodium hydroxide (NaOH) (Merck 6498).      [4,5]. PNP and NADH solutions were dispensed into the reaction cuvettes through the first reagent delivery system.  [6]. Reagent pipette delivery system imprecision In order not to interfere with the reagent pipette delivery system, the sample pipette was blocked. NaOH was dispensed as reagent one and PNP as reagent two. Four trials were run, with volumes ranging from 20 to 350 1 for reagent one and from 350 to 20 tl for reagent two [6]. In order to obtain a more accurate measurement of the reagent pipette delivery system imprecision, the spectrophotometric imprecision was subtracted from the global imprecision: spectrophotometric variance was subtracted from global variance. The spectrophotometric imprecision at these levels of O.D. was calculated from 30 measurements of the final solutions dispensed through the reagent one delivery system.
From this corrected variance, corrected standard deviation and coefficient of variation were calculated.
Sample dilution system inaccuracy and imprecision From a 10 mmol/1 PNP solution, three working solutions were prepared; one to check the 1/5 dilution, another for the / 10 and 1/20 dilutions, and a third for the 1

Analytical imprecision
To establish within-run imprecision, 30 samples of control sera were tested at three different levels, within the same run. To evaluate the between-run imprecision, one sample of each control serum was processed once a day for 30 days.

Specimen-related carry-over
Following the recommendations of the 'Comisi6n de Instrumentaci6n de la SEQC' [1,2], sample related carry-over was studied using a permutation order, in which three control samples with different concentrations were distributed along the sample chain. Mean and standard deviation were calculated both for noncontaminated samples and for the whole set of samples.   AST, glucose, cholesterol, urate, inorganic phosphate and total protein) (reagent two tray: ALT, AST, BUN, triglycerides, ALP, LDH and GGT).

Relative inaccuracy
Passing Bablok regression analysis was used to compare results of patient samples obtained in the Axon system with those obtained in the Hitachi 737 [7,8].

Results and discussion
Photometric inaccuracy Results of photometric inaccuracy at 340 and at 404 nm are shown in tables and 2 (respectively); the tables show the values of theoretical and observed absorbances and percentage inaccuracy. The bias observed at 404 nm ranged from -4"12% to 0"25%, and at 340 nm from -7"94% to -2"94%. Both inaccuracies were acceptable.  table 7 show the mean, the global, spectrophotometric and corrected standard deviation, and the coefficient ofvariation which ranged within 0"62% and 2"54%. As with photometric imprecision, the lower the absorbances, the greater the imprecision. Tables 8 and 9 show the results of imprecision and inaccuracy respectively. Imprecision ranges between 0"82% and 2"49%, and inaccuracy between -2"20% and 1"36%. Both were acceptable in all cases.

Analytical imprecision
Tables 10 and 11 show the results of within and betweenrun analytical imprecision respectively. For all studied analytes, the within-run imprecision was acceptable.
This contrasts with some values obtained for betweenrun imprecision which were surprisingly high.

Specimen-related carry-over
The results ofcarry-over studies are presented in table 12, which shows the mean and standard deviation for all samples (mean 1, SD 1), and for non-contaminated samples (mean 2, SD 2), for each analyte and level. The calculated F value is also expressed. In all cases, the calculated F value was less than the value of an F distribution for a p 0"05. This value for high and low levels (16 non-contaminated samples of 24 samples) is 2"30, and for medium level (nine non-contaminated samples of 12 samples) it is 3.31. Thus we can conclude that there is no significative sample-related carry-over. Specimen-independent carry-over In all method sequence combinations, the carry-over effect measured was less than twice the within-run imprecision of the method studied and can therefore be ignored.
Relative inaccuracy Table 13 shows the number of pairs compared, the studied range, slope andy intercept with their confidence intervals, and the regression coefficient (r) for each analyte.
The marked deviations of the slope from for ALP and LDH are due to methodological differences.

Conclusion
In general terms, the evaluation of the instrument was satisfactory, and, in our opinion, it fulfills the requirements for use in routine-work in a medium-size laboratory.
The photometer showed a slight tendency to give low abSorbance values at 340 nm.
The photometric imprecision was acceptable at the two wavelengths studied and no photometric drift was found over a 12 h working period. The reagents and sample delivery system showed a correct imprecision and the dilution system showed an acceptable inaccuracy and imprecision.