Urine screening for leucocytes and bacteria by dipstick and reflectance spectrophotometry

Abstract

In order to develop a rapid and reliable method for screening large numbers of urines for leucocytes and bacteria a dipstick method was used with colorimetric reading of colour changes with a reflectance spectrophotometer. One thousand consecutive urine specimens were tested by that method using a single dipstick for leucocyte esterase, nitrite, blood and protein in parallel with routine methods for enumeration of leucocytes by microscopy and quantitative culture for bacteria. Results of the four dipstick tests taken together had predictive values of 83.7% for a positive test for evidence of infection and 97.2% for a negative result. The false negative rate was 1%. Of the 191 urines with a significant bacteriuria (greater than 10(5) organisms/ml), 10 were false negatives by dipstick testing, representing 5% of all infected urines. Elimination of the need for culture on specimens that were negative by all four tests would reduce the workload by 36%.