Urine sample requests for microscopy, culture and sensitivity constitute the largest single category of specimens examined in microbiological laboratories. The main value of urine culture is to identify bacteria and their sensitivity to antibiotics (Higgins [84]).

Urine sampling should be considered in combination with clinical assessment and urinalysis to avoid unnecessary sample processing, which has time and cost implications for the microbiology laboratory (Pagana and Pagana [177]; Thomas [239]). A clinical assessment involves examining the odour, turbidity and colour; determining whether there are obvious signs of haematuria; and ascertaining whether there is pain, particularly around the suprapubic area. Urinalysis may reveal a high pH, the presence of blood, or positivity to leucocyte esterase (an enzyme released by white blood cells) or nitrite, all of which indicate a high probability of bacteriuria (Higgins [84], Pagana and Pagana [177]).

Urine may be collected using a midstream urine (MSU) clean‐catch technique or from a catheter using a sterile syringe to access the sample port (PHE [190]). To minimize the contamination of a specimen by bacteria (which may be present on the skin, the perianal region or the external genital tract), good hand and genital hygiene should be encouraged. Therefore, patients should be encouraged to wash their hands prior to collecting a clean‐catch MSU specimen and to clean around the urethral meatus prior to sample collection (Higgins [84]).

The principle for obtaining a midstream collection of urine is that any bacteria present in the urethra are washed away in the first portion of urine voided and therefore the specimen collected more accurately represents the urine in the bladder. A study conducted by Jackson et al. ([108]) using a urinary collection device showed a reduction in contamination compared with other MSU techniques. However, a study in pregnant women found that there was no difference between MSU, clean‐catch samples and morning samples with regard to potential contamination (Schneeberger et al. [221]).

The presence of a urinary catheter and the amount of time in situ are contributory factors in the development of a UTI. For every day the catheter remains in situ, the risk of bacteriuria is 5%, such that 50% of patients catheterised for longer than 7–10 days will have bacteriuria (Pellowe [182]). Although often asymptomatic, up to 30% of patients with bacteriuria will develop symptoms of catheter‐associated UTIs (CAUTIs), with 1–4% of those subsequently developing bacteraemia or sepsis, with an obvious impact on patient morbidity and increased hospital length of stay.

In order to minimize CAUTIs, catheters should only be inserted where absolutely necessary and should not be placed for the management of urinary incontinence except in exceptional circumstances when all other management methods have been unsuccessful. Additional techniques – such as closed catheter systems, antimicrobial coated catheters and carrying out drainage bag changes according to the manufacturer's guidance – can reduce the risk of a CAUTI (Hooton et al. [89], Loveday et al. [128]).