Analyzer random-access

Clinical analyzers can also be classified according to their degree of flexibiUty. Most of the modern systems are random access analyzers, for which the tests on various specimens are performed in any order programmed by the operator. Some analyzers operate in batch or profile mode, ie, they perform the same test or group of tests on every sample until the system is reset for another test or group of tests. 

Laboratory investigations play an essential role in medicine. Laboratory results are taken into consideration in about two thirds of all medical decisions in medical systems of industrialized countries today. The vast majority of clinical chemistry analyses are based on few analytical principles including photometry, ligand binding assays and potentiometry. For these standard methods complete automation has been achieved and multi-channel, random access analyzers realize several hundred analyses per instrument and hour on a very high level of user-friendliness. Consequently, clinical chemistry is very cost efficient today typically clinical chemistry analyses contribute less than 5 % of all costs of tertiary care hospitals. 

E694 Wunsch, C. and Steele, B. (1990). The task of validating a random access analyzer, the Ektachem 500. Clin. Chem. 36, 1013, Abstr. 289. 

Discrete analysis, in contrast with continuous-flow analysis, allows each specimen in a batch its own physical and chemical space, separate from every other specimen. Early discrete analyzers, such as the 1970 vintage robot chemist, mimicked the steps of manual human analysis. Subsequently, many discrete analyzers were developed and are still widely used in clinical laboratories. Centrifugal and random access analyzers are examples of instruments that use discrete processing. 

Most current chemistry and immunoassay analyzers are random-access analyzers. Manufacturers have steadily improved the mechanical reliability of these systems, and provided software that aMows technologists to operate the analyzers easily. 

The time allowed for a reaction to occur depends on a variety of factors. In some analyzers reaction time depends on the rate of transport through the system to the measurement station or on timed events of reagent addition (or activation) relative to measurement, or on both. In discrete random-access analyzers specimens and reagents are added to a cuvet in a timed sequence, and absorbance readings are performed at intervals to follow the course of each reaction. Usually, the total read time for a reaction in these systems is constrained to a maximum value defined by the manufacturer but may be programmed for a shorter period. 

Krouwer JS, Stewart WN, Schlain B. A multi-factor experimental design for evaluating random-access analyzers. Clin Chem 1988 34 1894-6. 

Eckert B, Blaut M, Holzderber M, Lenz H, Angermaier L, Franken N, et al. Electrochemilumi-nescent immunoassay for thyroxin and thyroxin binding capacity using the random-access analyzer Elecsys. Clin Chem 1995 41 S53. 

III. Olli 3000 Selective/batch/random access analyzer 24 Factor X... 

S Krais, H Lenz, A Rotter, M Simmeth, N Franken. Electro-chemiluminescent 3rd generation TSH assay using the random-access analyzer ELECSYS. Clin Chem 41 S52, 1995. 

Arsenazo III (quantitation at 650-700 nm) at pH 5.6-7.8, initially introduced on the Kodak Ektachem dry reagent multilayer system, has now been adapted for use on a number of wet chemistry random access analyzers. Magnesium shows no interference but gross hemolysis may depress the calcium result. At low calcium concentrations, this technique gives slightly higher results than either the flame or o-cresolphthalein complexone (approximately 0.1 mmol/liter higher at a concentration of 1.60 mmol/liter). 

We have measured FSH in unextracted urine on an AxSYM random-access immunoassay analyzer (Abbott laboratories, Abbott Park, IL) with a MEIA (microparticle enzyme immuno assay) reagent kit. In order to correct for dilution, creatinine was measured, and the urinary FSH was normalized for creatinine concentration. Urine and serum samples were obtained from 40 women between 32 and 55 years of age. All women were healthy, except for a benign gynecological illness for which they were admitted to our hospital. All women had normal renal function. On the day of operation, we took six serum samples from each patient, each at least an hour apart, in order to calculate the mean serum FSH concentration. During the same day, we collected an early-morning urine sample, 24-h urine sample, and a random void urine sample. 

Figure 1.3. A random-access continuous-flow analyzer (Chem 1-Technicon, USA), which aspirates sample (S) and necessary reagents (Rl, R2) sequentially from a two carousels (not shown). The resulting stream is air segmented and oil encapsulated (oil is shown as solid lines on top of liquids in the cups and on the walls of tubing to minimize the carryover. Detection is by a series of optical detector stations that discretely record gradual development of color during the flow transport. (P is a peristaltic pump.)...

The drawbacks of discrete analyzers are their mechanical complexity and high cost of operation. Sample cups, disposable cuvettes, rotors, and prepacked reagents increase the cost of individual assays above the acceptable limit for the strained budgets of most clinical laboratories. In addition, these machines are seldom used outside the clinical laboratory, because they are designed to handle three dozen of the most frequently required clinical tests. The advantages of the discrete approach are the ability of some of these instruments to perform assays via random access—which allows sequential assay of diverse analytes at will—and the capability of stat operation, which yields the analytical readout within 5-10 min after the machine has been switched on and a sample has been inserted by a technician. 

Today, a wide variety of discrete analyzers are avail-ble for clinical laboratories. Some of these arc gen-ra purpose and capable of performing many dilTerent eterminations. often on a random access basis. Oih-rs arc of more limited use intended for one or a few pccific determinations. Many of the general-purpose naly/ers use a combination of traditional chemical jsts and immunoassays in which aniibody-antigen itcractions arc used in the determination. Several encral-purpose analyzers are capable of performing lore than 100 tests, including the determinations hown in Table. 33-1. 

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