These questions and answers make recommendations about when and how primary care should investigate urinary symptoms. This guidance is based on evidence discussed in detail in Health Protection Agency (www.hpa.org.uk
) and PRODIGY (www.prodigy.nhs.uk
) guidelines and in the other key references quoted.
When should I send a urine specimen in patients with possible urinary tract infection?
In adults we recommend a urine specimen in:
- Failed antibiotic treatment or persistent symptoms in all individuals.71
- Recurrent UTI.71
- Suspected pyelonephritis.72
- All men with urinary symptoms consistent with infection.73
- Catheterised patients with fever 38°C, rigors, vomiting, new onset confusion, or costovertebral tenderness (see “In catheterised patients” below).74
- Anatomical abnormalities of the genitourinary tract.73
- Renal impairment.73
- Suspected or known immunosuppression—for example, chemotherapy.
- In sexually active men and women with urinary symptoms consider Chlamydia trachomatis infection and send appropriate specimens.
Waiting for the results of urine culture in patients with suspected UTI delays diagnosis and is not cost effective. Conversely, prescribing antibiotics to all patients with urinary symptoms will lead to overuse of antibiotics. Empirical antibiotic treatment in acute, uncomplicated UTI in women77
should be based on the severity and classic nature of the symptoms and urine dipstick results, with the exception of the specific situations listed in the recommendations above. Submission of a urine specimen before starting treatment may be helpful to identify antibiotic susceptibility, particularly in the event of treatment failure, although it should not delay treatment.78
Patients with failed antibiotic treatment or recurrent UTI are more likely to have an infection caused by a bacterium that is resistant to antibiotics.71
Therefore, urine culture and susceptibility is used to confirm that antibiotic choice is appropriate.
Patients with renal impairment or abnormalities of the genitourinary tract are more likely to have ascending infection/pyelonephritis and antibiotic resistant bacteria, and it is therefore most important to confirm antibiotic susceptibility.73
Similarly, bacteraemia is much more common in patients with pyelonephritis or fever than in uncomplicated UTI (15–20%) and, therefore, it is important to confirm antibiotic susceptibility73
in these cases.
In children we recommend a urine specimen from:
- Neonates or infants with:
- Children of any age with:
Guidance is based on recommendations of the Royal College of Physicians for the management of acute UTI in children.79
Greater opportunities for health gain lie in improving the detection and treatment of acute UTI in children than in the detection and management of vesico–ureteric reflux.79
Increased submission of urine samples from children with the above signs or symptoms leads to greater detection of UTI.80
Fever alone can produce pyuria in children,81
highlighting the need for laboratory diagnosis of infection.
In the elderly we recommend a urine specimen if:
- Dysuria (burning or pain passing urine).
- Fever 38°C.
- Acute change in continence.
- Fever plus one of, new or worsening:
Do not send urine from elderly patients if:
- Asymptomatic, irrespective of dipstick nitrite/leucocyte results.
- Subacute or chronic non‐specific decline in health statusas the only symptom because this is a non‐specific sign.
- Chronic incontinence without other symptoms.
- Catheterised and asymptomatic patients.
Asymptomatic bacteriuria is extremely common82
(20% of >
65 year olds and 50% of >
80 year olds or patients with dementia) and is not associated with increased morbidity.82
Routine dipstick testing of urine samples for nitrite and leucocytes, and urine culture results in unnecessary antibiotics and treatment of asymptomatic bacteriuria.83,84
In catheterised patients74,85we recommend a urine specimen if:
- Fever or rigors without identified cause.
- New onset delirium or costovertebral tenderness.
- Pre‐urological surgery.
Bacteriuria is present in most patients with longterm urinary catheters (>
28 days), but the incidence of fever in longterm catheterised patients is low (approximately one episode/100 days of catheterisation). In 50% of catheterised patients with fever, bacteraemia is present and is caused by ascending urinary infection.85
In patients with paraplegia, other non‐specific symptoms, such as vomiting and increased spasticty, may indicate urinary tract infection.
Antibiotic treatment of asymptomatic bacteriuria in the presence of a catheter does not improve outcome.
When should I use urine dipsticks?
- Suspected uncomplicated UTI in adults in combination with assessment of clinical symptoms.
- Suspected UTI in children, to confirm suspicions of UTI, but a urine specimen should be submitted irrespective of results.
- Dipsticks are not reliable in young children (under 2 years).
- Dipstick results should always be interpreted in the context of clinical symptoms.
Testing for leucocytes (leucocyte esterase) and bacteria (nitrite) in combination appears at present to be the best means of dipstick testing.
Positive blood or leucocytes alone can be found in UTI but are also found in the urethral syndrome (urethral inflammation),86
which does not warrant antibiotic treatment. Nitrite testing alone is not recommended.87
A negative nitrite and leucocyte test can often be used to rule out UTI, because it has a reported negative predictive values of up to 95% or above,78
although reported meta‐analysis sensitivity figures are lower (80–90%).88,89
These differences probably relate to clinical context. A positive result does not necessarily indicate infection: reported specificity is 60–80%.78,88,89,90
Several guidance sources78,87,91
state that subsequent culture in uncomplicated lower UTI in women is not necessary, but stress the need for culture in the other situations listed above. The European Confederation of Laboratory Medicine guidelines recommend a “clinical filter” after the dipstick test is performed, to put the result in the clinical context before decision making.87
No robust simple algorithms combining symptom scores and dipstick results are available,92
and there is no clear consensus as to whether urine testing of any form is necessary in all women with possible UTI, in view of the usual self limiting course of the disease.93
When reading the dipstick test it is important to wait for the time recommended by the manufacturer. Nitrite is produced by the action of bacterial nitrate reductase in urine. Because contact time between bacteria and urine is needed, morning specimens are most reliable.94
It should also be noted that falsely negative results can be obtained with bacteria that cannot reduce nitrate, such as enterococci. Proteinuria occurs in UTI but is also present in other conditions and is relatively non‐specific. Other diagnoses should be considered for isolated proteinuria.95
How should I interpret urine dipstick results?91
Figure 1 provides a guideline flowchart of the interpretation of urine dipstick results.
Figure 1Guidance on how to interpret urine dipstick results. HPA, Health Protection Agency; NPV, negative predictive value; UTI, urinary tract infection.
How should I obtain a urine specimen?
- A midstream specimen should be obtained from men, women, and older children. In females, cleaning with water or antiseptic or holding the labia apart does not reduce contamination.96,97,98,99
- In toddlers, a potty washed in hot water with washing up liquid is better than a bag urine.100A urine collection pad in a nappy may be used for infants.101
- Refrigerate specimens to prevent bacterial overgrowth, or use specimen pots containing boric acid.102,103Because boric acid is antibacterial, specimen pots should be filled to the indicated level to obtain the optimum boric acid concentration.
How should I interpret laboratory results?
- More than 105 organisms/ml (or >108/litre) of pure growth (single bacterium isolated) obtained from a midstream specimen of urine has historically been considered diagnostic of UTI.
- However, lower counts of pure growth (103/ml or less), or a mixed growth of two organisms only (>105/ml) may also indicate UTI in patients with signs and symptoms of UTI.87
Mixed growth from a midstream urine sample usually indicates that the urine has been contaminated on collection by perineal flora; this is often indicated by the presence of epithelial cells on the microscopy report. However, patients with longterm indwelling catheters may have infections with mixed organisms, although is should be emphasised that mixed growth from a cultured specimen of urine does not require antimicrobials in the absence of signs/symptoms of infection.