Laboratory diagnosis

The laboratory diagnosis of UTI depends on careful collection, examination and culture of urine. Collection of urine 1

It is best to collect the first urine passed in the morning, when it is highly concentrated and any bacteria have been incubated in the bladder overnight. Preferably the urine should be taken to the laboratory immediately, but it can be stored for up to 24 hours at 4°C to prevent bacterial multiplication.

• Midstream specimen of urine (MSU). This is best collected from a full bladder, to allow at least 200 mL of urine to be passed before collection of the MSU. It is important that the urine flow is continuous, and the container is moved in and out of the stream collecting at least 20 mL. o In women, a tampon should first be inserted and the vulva washed with clean water (to avoid contamination with vaginal and vulval organisms). The labia are then held apart with the fingers to prevent contact with the urinary stream while the specimen is collected.

o In males, the foreskin (if present) is retracted and the glans washed with clean water.

• Catheter specimen of urine (CSU). In women who have difficulty with collecting an uncontaminated MSU (as is commonly the case in the elderly, the infirm and the grossly obese), a short open-ended catheter can be inserted and a specimen collected after 200 mL has flushed the catheter.

• Suprapubic aspirate of urine (SPA). This is an extremely reliable way to detect bacteriuria in neonates and in patients where UTI is suspected but cannot be confirmed because of low colony counts or contamination in an MSU. Under local anaesthetic, a needle (lumbar puncture needle in adults) is inserted into the very full bladder about 1 cm above the pubic symphysis, and 20 mL is collected by a syringe. Any organisms in an SPA specimen indicate UTI.

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