Automated microbiology: an asset to urine testing

While the analysers represented an advance in automation, providing an improvement in workflow and automated the reading of the test strips, the main drawback, as time and innovation progressed, was the requirement for the operator always be present. As direct loading of patient samples was not possible, the test strips had to be dipped manually and placed on the analyser.

Analysers were used primarily as a first-line negative predictor for urinary tract infection (UTI), the technology being based on the presence or absence of biochemical markers in the urine sample – usually a combination of protein, blood/haemoglobin, nitrite or leucocyte esterase. Samples negative for these parameters indicated ‘no evidence of infection’ with a negative predictive value in the order of 96–97% and as a consequence did not require further culturing. While performing automated dipstick analysis, some laboratories continued with manual microscopy in order to visualise and report any sediment particles present.

Particle theory
The development of particle counters based on flow cytometry with particle scattergrams or particle image capture represented the next stage in automated urine analysis. This indicated a move away from biochemical analysis to physical analysis of the urine sediment, more in tune with the reference method of urine sediment examination. Analysers could now provide not only automated microscopy but also be the starting point for introducing a UTI screening protocol and provided rack-handling systems so that patient samples could be loaded directly on the analyser. Operators were then able to leave the analyser to process the work and carry out other duties, only returning to the analyser sometime later when the work was completed.