Leukocyte esterase on a urine dipstick: signs of white cells and infection

White blood cells, also called leukocytes, release an enzyme called leukocyte esterase. A dipstick pad changes colour when the enzyme is present, indicating white cells in the sample. Lab Tests Online UK explains that urinalysis can reveal white blood cells and bacteria in urine when an infection has put them there, and GPnotebook lists leukocytes among the substances a reagent strip can test for in a fresh urine sample.

Its significance depends on the person. White cells in urine point to inflammation somewhere in the urinary tract, most often infection, but the dipstick does not identify the cause or the organism.

The NHS lists symptoms of urinary tract infection: pain or burning when passing urine, needing to pass urine more often or urgently including at night, cloudy urine, blood in the urine, lower tummy or back pain, a high or very low temperature, and tiredness. A GP may do a urine test, though not always, and may offer antibiotics. In older frail people and in people with a catheter, symptoms may include confusion or worse incontinence.

NICE guideline NG224 on UTI in under 16s sets out a dipstick strategy for children 3 years or older: if both leukocyte esterase and nitrite are positive, assume UTI and give antibiotics; if leukocyte esterase is positive and nitrite negative, send urine for microscopy and culture but do not start antibiotics unless there is good clinical evidence; if leukocyte esterase is negative and nitrite positive, start antibiotics if the sample was fresh and send for culture; if both are negative, do not treat as UTI or send culture and explore other causes. NICE notes dipstick testing for these two markers is diagnostically as useful as microscopy and culture. For adults, clinicians combine the dipstick with symptoms and local guidance.

A fresh mid-stream sample reduces contamination. Lab Tests Online UK describes cleaning the genital area first and collecting the middle part of the stream. A dipstick can be read in the clinic immediately; if there is something unusual, the sample may be sent to the laboratory for microscopy and culture, which takes several days. Vaginal discharge or skin contamination can cause a positive leukocyte esterase without bladder infection, so a clean sample matters.

GPnotebook, citing NICE, notes that leukocyte esterase may be indicative of an infection outside the urinary tract, which may need to be managed differently. White cells in urine without bacteria can reflect inflammation from kidney stones, interstitial cystitis, kidney disease or sexually transmitted infections. Conversely, a negative leukocyte esterase does not exclude UTI in someone with strong symptoms.

The NHS says chronic UTIs can be difficult to diagnose because urine tests do not always pick up the infection, and that if symptoms persist despite treatment you should ask your GP to refer you to a specialist.

The NHS suggests paracetamol for pain, rest, enough fluids to pass pale urine regularly and avoiding drinks that irritate the bladder such as fruit juices, coffee and alcohol. Women and girls aged 16 to 64 who are not pregnant may see a pharmacist. Ask for an urgent GP appointment or NHS 111 if you are 65 or older, a man, pregnant, have diabetes, a catheter or a weakened immune system, have blood in the urine, back or lower tummy pain, symptoms that worsen quickly or last 48 hours after treatment, or keep getting UTIs. Call 999 for confusion, drowsiness or difficulty speaking.

Treatment is guided by symptoms and, where sent, the culture result. Repeated infections need review, which may include a short course of preventative antibiotics, oestrogen in some post-menopausal women, or specialist assessment, as the NHS describes.