Previous: CONTINUOUS AMBULATORY PERITONEAL DIALYSIS (CAPD)

CONTINUOUS FLOW ANALYSER

Typical Number in Hospital: 2

Cost Bands: 5,6,7

References: 9

This is one type of automated chemical analyser which may be used in the clinical chemistry laboratory to estimate the concentration of a range of ions and molecules found in samples of body fluids such as blood and urine.

The basic technique is to move the sample to be tested (usually in diluted form), together with a quantity of a reagent, along a narrow tube to a colorimeter which will identify the original concentration from the optical density of the sample. The chemical reaction necessary to produce the result takes place as the bolus of fluid passes along the tube. Special conditions may be created if the particular analytical process requires it, such as heating, or introducing the sample to the reagent via a dialyser if other constituents of the sample might interfere with the reaction.

Each bolus of fluid is separated from the next by a bubble of air which acts to clean the inside of the tube and prevent contamination of one sample by the next. Usually samples alternate with a washing mixture so that this separation is optimized.

Several tests may be carried out at the same time using separate tubes and processes according to the test being performed. An example of a continuous flow analyser is the Technicon SMA (sequential multiple analyser) series which may perform six or twelve separate tests at the same time. Later versions are able to analyse 20 parameters on 0.4 ml samples at a rate of 150 samples/hour.

This type of analyser is very popular. Its main disadvantage is that every available test is normally performed on every sample, with resultant (sometimes unnecessary) cost.

The addition of a computer enables an extension of the automatic process to the printing and mailing of the results or direct communication over computer lines.