Leucocyte esterase

A urine dipstick indicates a urinary glucose of >25 mmol/L but is negative for nitrites and leucocyte esterase. 

The urinary tract is normally sterile and dipsticks or reagent test strips are used to detect bacteriuria (presence of bacteria in the urine) by testing for nitrites (all common UTI bacteria convert nitrate to nitrite) or leucocyte esterase (enzyme indicating the presence of white blood cells). 

Where only one symptom or sign of UTI is present, a dipstick test positive for leucocyte esterase or nitrites is associated with a high probability of bacteriuria (80%). If both leucocyte esterase and nitrites are negative, this is associated with a much lower probability of bacteriuria (approximately 20%) (SIGN, 2006). 

However, a small study of younger women (16-59 years of age) presenting with a history of two symptoms - dysuria and frequency - but dipstick negative for both leucocyte esterase and nitrites, demonstrated that treatment with short-course trimethoprim significantly decreased the median time to resolution of dysuria (76% of women in trimethoprim group were free of dysuria by day 3 compared with 26% of placebo group). The authors concluded that their results supported the use of symptoms alone to diagnose and treat UTI without urinalysis (Richards et al., 2005). 

Luedecke, L.O. 1964. Relationship between California Mastitis Test reactions and leucocyte count, catalase activity and A-esterase activity of milk from opposite quarters. J. Dairy Sci. 47, 696. 

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