Screening for bacteriuria with Clinitec-200

A comparison of chemical dipsticks read visually or by photometry in the routine screening of urine specimens in the clinical microbiology laboratory

Two different commercially available urine dipsticks were evaluated to determine their usefulness as a screening test for the detection of non-infected urine specimens. The reactions of both dipstick strips were read visually and, in addition, one was read by semi-automated reflectance photometry. 2928 consecutive routine urine specimens received by the microbiology laboratory during normal working hours underwent testing by the conventional method of microscopy and culture and the results were compared with those obtained by dipstick testing. There were poor correlations between microscopy for red and white blood cells and dipstick results for blood and leucocyte esterase respectively. The dipsticks had a low positive predictive value (PPV) in identifying infected urines. In contrast, dipsticks had a very high negative predictive value (NPV) of 98.6-99.5% and correctly identified a significant proportion (about 1/3) of non-infected urines as reported by the conventional method. Introduction of dipstick testing of urine specimens in our hospital has led to significant time saving as dipstick-negative urines are not processed further (except for specific clinical indications) and there has also been a significant decrease (25%) in the number of specimens submitted to the laboratory. Further efficiencies may be obtainable with increased automation.

Urine transparency as an index of absence of infection

A visual assessment of the clarity of urine was used as an exclusion test to indicate the absence of infection; verified by dipslide culture, it was applied to 363 urine samples collected from patients attending 2 adult nephrology clinics over a period of 6 months. The crimped aluminium bowl used for collection of samples assisted the assessment of clarity. The sensitivity of the method compared with dipslide culture was 73%, with specificity and efficiecy both 58%. The predictive value of a negative test (clarity) was 97% with a false negative rate of 3%, enabling this simple examination to be used as an exclusion test for further testing. In simple terms, a clear urine is unlikely to be infected. It is also an advantage to have an immediate indicator of the absence of infection available at the clinic. Analysis of only those urines assessed as cloudy could result in financial savings and, from the clinics, a 56% reduction in workload.