Leucocyte esterase and nitrite dip sticks

It is not helpful, nor cost-effective, to send routine MSUs prior to therapy on healthy, non-pregnant women presenting with acute cystitis. It is reasonable, however, to test the urine with a leucocyte esterase and nitrite dipstick. This has a sensitivity of 75 – 95% predicting culture-proven infection. Antibiotics should then be prescribed to those patients who have a positive result for either test. MSUs should only be sent from women with complicated urinary tract infection (Table Risk factors of occult upper urinary tract infection), screening for asymptomatic bacteriuria of pregnancy, or those women who have failed to respond to first-line therapy.

Table Risk factors of occult upper urinary tract infection

Physiological
Pregnancy
Diabetes mellitus
Anatomical
Urinary tract abnormality
Urinary stone
Indwelling catheter
Recent instrumentation
Past medical history
Previous recurrent urinary tract infection, previous urinary tract infection as a child, previous pyelonephritis, symptoms present for more than 7 days before presentation, any immunosuppressive condition
Urogenital ageing in the postmenopausal woman

Mid-stream sample of urine (MSU)

For many years nurses have spent much time and energy collecting mid-stream urine specimens from patients. In hospital they have used the modified nursing procedure from the Royal Marsden, which requires cleansing of the external genitalia and urethral meatus with three sterile wipes before the patient is required to void the urine into a sterile bowl. The patient is asked to micturate and the mid-stream part of the urine flow is sampled. This reduces the risk of contamination by normal flora in the distal urethra, which are washed away by the initial urinary stream. In non-ambulatory patients who do not have perineal cleaning, the urine specimens are heavily contaminated with mixed faecal and skin flora. However, no difference was found between using a sterile mid-stream sample of urine pack and non-sterile wipes in a group of women over the age of 65.

In young ambulatory patients, a study using either sterile bowls or non-sterile paper cups as a receiver for the mid-stream sample of urine was carried out. There was no difference in the contamination rate using an easy-to-handle, cheap paper cup.

Evaluating bacterial contamination from urine sampling techniques, it has been found in a prospective study that holding the labia apart is actually the most significant action when trying to obtain a “clean” mid-stream sample of urine sample. This decreased bacterial contamination from 31.1 to 13% (P < 0.01) in healthy young women. This is not surprising since the urine leaves the female urethra orifice in a broad stream, splashing on the labia, hosing down vaginal squamous cells, hairs, and bacteria into the receptacle for catching the urine. A full, clean-catch, mid-stream sample of urine technique is difficult and time consuming to understand and perform. The simple procedure of asking the patient to hold her labia apart whilst catching the urine in a paper cup significantly decreases contaminated specimens.

Having gone to all the trouble of obtaining a reasonably reliable mid-stream sample of urine, the urine inevitably then spends 8 hours on a hot treatment room shelf awaiting collection! This ruins the specimen by bacterial overgrowth. Ideally, the specimen needs to go to the laboratory within 2 hours. In general practice this is rarely possible, and so the urine sample should be refrigerated until transported to the laboratory.

What follow-up is required of women with urinary tract infections?

No follow-up and no post-urine cultures are required for a simple acute uncomplicated cystitis in a well woman. If she remains symptomatic by the third day of treatment, an mid-stream sample of urine should be sent for culture and sensitivity. Any woman with a complex urinary tract infection, or during pregnancy, should be closely followed. Two weeks after finishing treatment for a proven complex urinary tract infection, an mid-stream sample of urine should be sent for follow-up culture.

In the small percentage of women who have recurrent urinary tract infections (>2 urinary tract infections in 6 months or >3 in a year), there is concern that these women may have a stone or an obstructive uropathy as an underlying aetiology. However, on ultrasound, intravenous pyelography, or cystoscopy, fewer than 5% have a demonstrable abnormality.

For women on continuous prophylaxis, it is essential to send an mid-stream sample of urine if they become symptomatic, as this implies a reinfection with a resistant organism. It is imperative to know the culture and sensitivity to make the correct antimicrobial decision.

Trimethoprim

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