Urine culture

Urinary Tract Infection (UTI) is one of the commonest bacterial infections presenting in primary and secondary care and includes asymptomatic bacteriuria, simple cystitis, prostatitis, pyelonephritis and urosepsis. It is most common in women. It is usually caused by ascending infection from the periurethral area by colonising flora from the gastro-intestinal tract.

It can be classified as uncomplicated (acute cystitis in females) or complicated (all UTI in males, upper UTI in females, pregnancy, urinary tract abnormality/instrumentation, immunosuppression). Culture results from catheter specimens of urine should be interpreted with caution due to the difficulty in obtaining a sample that truly reflects bladder pathogens.

The accuracy of dipstick testing in adults aged >65 years can vary, so if UTI is suspected in this age group, a full clinical assessment is required,¹ together with urine for culture if indicated.

It is estimated that 10% of males and 20% of females over the age of 80 have asymptomatic bacteriuria, making UTI difficult to diagnose.²

Patients in whom a urine sample should be sent for culture:

• pregnant woman, man, child/young person under 16 years presenting with symptoms of lower UTI³
• any patient presenting with features of acute pyelonephritis⁴
• unwell babies, children and young people if suspicion of UTI but no typical signs/symptoms^5,6
• other complicated UTI (structural abnormality/instrumentation, immunosuppression)

A mid-stream or clean catch specimen is preferred to avoid contamination with peri-urethral organisms. Peri-urethral cleaning before sampling has little impact on contamination rates.

• Non-pregnant women with symptoms of simple UTI
• Asymptomatic pregnant woman early in pregnancy as screen for bacteriuria⁷
• Babies, children and young people 3 months and over with symptoms and signs of an infection other than UTI (unless diagnostic uncertainty and they remain unwell)
• Routine retesting is not required in any age group if asymptomatic after treatment

• Ongoing symptoms and a negative, mixed or unusual organism on first culture e.g. Staphylococcus aureus (may be contaminant or associated with renal pathology)
• Failure to respond to treatment
• In children, a second sample may be required for confirmation (a clean sample may be difficult to obtain)

1. NICE QS90 Urinary tract infections in adults. Published June 2015. Available from: https://www.nice.org.uk/guidance/qs90
2. Public Health England Guidance - SMI B 41: investigation of urine. Published July 2014, Last updated January 2019. Available from: https://www.gov.uk/government/publications/smi-b-41-investigation-of-urine
3. NICE NG109 Urinary tract infection (lower): antimicrobial prescribing. Published: October 2018. Available from: https://www.nice.org.uk/guidance/ng109
4. NICE NG111 Pyelonephritis (acute): antimicrobial prescribing. Published October 2018. Available from: https://www.nice.org.uk/guidance/NG111
5. NICE NG224 Urinary tract infection in under 16s: diagnosis and management. Published July 2022. Available from: https://www.nice.org.uk/guidance/ng224
6. NICE NG143 Fever in under 5s: assessment and initial management. Published November 2019, Last updated November 2021. Available from: https://www.nice.org.uk/guidance/ng143
7. NICE NG201 Antenatal care. Published August 2021. Available from: https://www.nice.org.uk/guidance/ng201