Using the Urine Dipstick to Screen Out Unnecessary Urine Cultures: Implementation at One Facility

Extract

This study examined the utility of performing urine cultures on biochemically negative urine specimens and details the implementation of a policy to cancel these cultures. Four reactions of the Multistix® SG (Bayer, Elkhart IN) urine dipstick (protein, occult blood, leukocyte esterase, and nitrite) were used as biochemical indicators. A three-month retrospective study examining the results of 843 urinalysis/urine culture pairs indicated that one-third of these cultures were probably unnecessary (negative dipstick/negative culture). Based on these results, a policy was implemented to screen those urine samples having both a urinalysis and urine culture ordered. Over a six-month period, 6,192 urine specimens were evaluated. Of these, 36% (2,260 cultures) were cancelled. Of the 3,932 samples cultured, 22.4% (883) were true positives (positive dipstick/positive culture) while 31.6% (1245) had a positive dipstick but grew organisms considered contaminants. The false positive rate was 40% (positive dipstick/negative culture), and the false negative rate was 6%. Implementation of this policy reduced the number of urines cultured by 36%.

Published reports have demonstrated that the urine dipstick can be used as a screen to eliminate unnecessary urine cultures.^1–4 These reports indicate that using leukocyte esterase activity and urinary nitrite production to indicate pyuria and bacteriuria, respectively, had both a high sensitivity (79.1% to 88.7%) and a high negative predictive value (90%). The sensitivity increased to 91% to 97% and the negative predictive value rose to 96% when four biochemical markers (leukocyte esterase, nitrite, protein, and occult blood) were used as screening parameters. These figures were similar in…

ABBREVIATIONS: UA = urinalysis.