The laboratory investigation of urinary tract infections
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The laboratory investigation of urinary tract infections. Key messages Introduction Uncomplicated vs complicated UTI When is urine culture not helpful? When is urine culture helpful? Testing for asymptomatic bacteriuria Chlamydia trachomatis urethritis. Contents.

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The laboratory investigation of urinary tract infections

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The laboratory investigationof urinary tract infections

Key messages


Uncomplicated vs complicated UTI

When is urine culture not helpful?

When is urine culture helpful?

Testing for asymptomatic bacteriuria

Chlamydia trachomatis urethritis


Women with symptoms of uncomplicated UTI do not require a urine culture

Screening for asymptomatic bacteriuria is not recommended except in pregnant women

Chlamydia trachomatis urethritis can cause similar symptoms to a UTI

Key messages


Approximately 50% of all women will have a UTI, and 25% of these will experience recurrent infections

In 2005, almost 800 000 urine cultures were performed in NZ at a cost of approx $12.5 million

Patients with asymptomatic bacteria do not benefit from antibiotic treatment

Consider C. trachomatis infectionif patients present with symptoms of a UTI + suspicious sexual history



Uncomplicated versus complicated UTI

  • People with symptoms of uncomplicated UTI do not require a urine culture. They can be treated empirically and no follow-up is required unless symptoms do not improve.

  • People with complicated UTI require urine testing for culture and susceptibility testing


Uncomplicated UTI…

Complicated UTIs are those occurring in…

In women with classical presentation of uncomplicated UTI, treatment can begin based on the strength of clinical presentation.

In women with dysuria and vaginal symptoms consider both a UTI and STIs.

A dipstick positive to nitrites or leukocytes has a probability of a UTI of about 80%

A dipstick negative to both nitrites and leukocytes, has a probability of a UTI of about 20%.

Urine culture is not helpful for women with uncomplicated lower urinary tract infections as it does not improve outcomes.


Urine culture should be performed for:

Women with a UTI with complicating features

All pregnant women

Men with suspected UTI

Suspected acute pyelonephritis


When is urine culture helpful?


Abnormal urinary tract e.g. stone, reflux, catheter,

Impaired host defences e.g. pregnancy, diabetes, immunosupression,

Impaired renal function,

Suspicion of pyelonephritis,

More than three UTIs in one year, or

UTI recurrence within two weeks.

Complicating features in women include:


Women with asymptomatic bacteriuria in early pregnancy have a 20-30 fold increased risk of developing pyelonephritis, premature delivery and low birth weight infants.

All pregnant women should be screened for asymptomatic bacteriuria at 12-16 weeks gestation.

If bacteriuria is detected by screening, the patient should be treated and a urine culture performed monthly throughout the pregnancy

Urine culture is recommended for pregnant women


All UTIs in men are considered complicated, therefore a urine culture is indicated, even if the urine dipstick is negative.

Urine culture is indicated for lower UTI in Men


Dipstick testing of the urine may be useful if clinical findings are equivocal

Antibiotics should be commenced while waiting for culture results

Post-treatment urine cultures are recommended one to two weeks after antibiotic therapy

A urine culture is indicated when acute pyelonephritis is suspected


Signs and symptoms of acute prostatitis include fever, dysuria, pelvic or perineal pain, and cloudy urine

Urine culture should be performed

If urine culture is negative, STIs (C. trachomatis, N. gonorrhoea) should be excluded.

Acute Prostatitis


Chronic prostatitis should be considered in men with dysuria and frequency, no signs of acute prostatitis, and with recurrent UTIs.

Gram-negative bacilli are most common cause, but enterococci and Chlamydia have been associated with chronic infection.

Chronic Prostatitis


Screening for asymptomatic bacteriuria

The prevalence of asymptomatic bacteriuria varies from 1-5% to 100% in selected population groups.

Asymptomatic bacteriuria is a microbiological diagnosis based on the isolation of a specified count of bacteria in the absence of signs of UTI.


Testing for asymptomatic bacteriuria not required in elderly people

Asymptomatic bacteriuria in the elderly occurs frequently.

There is no benefit from treating asymptomatic bacteriuria.

The diagnosis of UTI in this age group should be made based on clinical signs and symptoms.


All in-dwelling catheters eventually become colonised with bacteria.

Regular urine culture or dipstick testing is not indicated for people with in-dwelling catheters


Asymptomatic bacteriuria and people with spinal cord injuries

People with spinal cord injuries have a high prevalence of bacteriuria, as well as high incidence of symptomatic urinary tract infection

Urine culture should be performed when UTI is suspected, for example: when the patient has non-specific symptoms, such as vomiting and increased spasticity.


Always consider C. trachomatis urethritis when UTI is suspected

C. trachomatis urethritis is commonly asymptomatic, but may present with dysuria

C. trachomatis infection should be considered when a UTI is suspected and the patients has a suspicious sexual history

Sterile pyuria (white cells in the urine but no urinary pathogen isolated) or positive leucocyte esterase test on urinalysis may be due to urethritis rather than a UTI

Chlamydia trachomatis urethritis


Diagnosis of C. trachomatis urethritis in men, and screening in men and women:

Testing can be performed on a first pass urine sample (no urination for one hour prior to collection)

Urethral swabbing in men or women has little advantage over urine testing. It may also be painful and poorly tolerated.

In women endocervical swabs, high vaginal swab and urethral sample (either first-catch urine or urethral swab) will exclude most causes of genital tract infection.

Testing for C. trachomatis


If C. trachomatis infection is detected on a urine sample, a complete STI evaluation is recommended to exclude co-infection with other sexually transmitted bacteria, protozoa and viruses.

Positive C. trachomatis results

Evidence based guide ‘Laboratory Investigation of UTIs’

Interactive online quiz

Quiz feedback

UTI Clinical Audit pack for general practice

Individual UTI investigation feedback for GPs

Resources available from bpacnz on the lab investigation of UTIs include:


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