Lower urinary tract infection - Cystitis : infection and/or inflammation of the bladder.
Presentation: frequent voiding of small volumes, dysuria, urgency, offensive urine, suprapubic pain, haematuria, fever, and incontinence.
Investigation
Dipstick of midstream specimen of urine (MSU)
White blood cells (indirect testing for pyuria)
Leukocyte esterase activity detects the presence of white blood cells in the urine. Leukocyte esterase is produced by neutrophils and causes a colour change in a chromogen salt on the dipstick. Not all patients with bacteriuria have significant pyuria (sensitivity of 75 - 95% for detection of infection i.e. 5 - 25% of patients with infection will have a -ve leukocyte esterase test suggesting, erroneously, that they have no infection).
- False -ves (pyuria present, negative dipstick test) concentrated urine, glycosuria, presence of urobilinogen, consumption of large amounts of ascorbic acid.
- False +ves (pyuria absent, positive dipstick test) contamination.
Remember, there are many causes for pyuria (and therefore a +ve leukocyte esterase test) occurring in the absence of bacteria on urine micro-scopy. This is so-called sterile pyuria and it occurs with TB infection, renal calculi, bladder calculi, glomerulonephritis, interstitial cystitis, carcinoma in situ. Thus, the leukocyte esterase dipstick test may be truly positive, in the absence of infection.
Nitrite testing (indirect testing for bacteriuria)
Nitrites are not normally found in urine and their presence suggests the possibility of bacteriuria. Many species of gram-negative bacteria can convert nitrates to nitrites and these are detected in urine by a reaction with the reagents on the dipstick which form a red azo dye. The specificity of the nitrite dipstick for detecting bacteriuria is >90% (false +ve nitrite testing can occur with contamination). Sensitivity: 35 - 85% (i.e. false -ves are common a negative dipstick in the presence of active infection); less accurate in urine containing fewer than 105 organisms/ml. So, if the nitrite dipstick test is +ve, the patient probably has a UTI, but a -ve test often occurs in the presence of infection.
Cloudy urine which is +ve for WBCs on dipstick and is nitrite +ve is very likely to be infected.
Microscopy of midstream specimen of urine (MSU)
- False -ves low bacterial counts may make it very difficult to identify bacteria, and the specimen of urine may therefore be deemed to be negative for bacteriuria, when in fact there is active infection.
- False +ves bacteria may be seen in the MSU in the absence of infection. This is most often due to contamination of the MSU with commensals from the distal urethra and perineum (urine from a woman may contain thousands of lactobacilli and corynebacteria, and these organisms are derived from the vagina). These bacteria are readily seen under the microscope, and although they are gram-positive, they often appear gram-negative (gram-variable) if stained.
If the urine specimen contains large numbers of squamous epithelial cells (cells which are derived from the foreskin, vaginal, or distal urethral epithelium), this suggests contamination of the specimen, and the presence of bacteria in this situation may indicate a false +ve result. The finding of pyuria and red blood cells suggests the presence of active infection.
Further investigation
Determined by the clinical scenario. If this is a one-off infection in an otherwise healthy individual, no further investigations are required. However, further investigations are required if:
- the patient develops symptoms and signs of upper tract infection (loin pain, malaise, fever) and therefore acute pyelonephritis, a pyonephrosis, or perinephric abscess is suspected
- recurrent UTIs develop.
- the patient is pregnant
- unusual infecting organism (e.g. Proteus), suggesting the possibility of an infection stone
These further investigations will include a KUB X-ray (looking for infection stones in the kidney; avoid in pregnant women) and a renal ultrasound.
Non-infective cystitis
- Pelvic radiotherapy (radiation cystitis bladder capacity is reduced and multiple areas of mucosal telangectasia are seen cystoscopically)
- Drug-induced cystitis (e.g. cyclophosphamide treatment)
- Haemorrhagic cystitis
Urethritis
is inflammation of the urethra. Urethritis in men is a sexually transmitted disease, which presents with dysuria and urethral discharge.
- Gonococcal urethritis (GU) is caused by the gram-negative dipplococcus Neisseria gonorrhoea (incubation 3 - 10 days). Diagnosis is on cultures from urethral swab. Treatment involves a single dose of cefotaxime or course of ciprofloxacin. Sexual contacts must be informed and treated.
- Non-gonococcal urethritis (NGU) is mainly caused by Chlamydia trachomatis (incubation 1 - 5 weeks). Treat with a single dose of azithromycin and 7 days of doxicycline. Transmission to females results in increased risk of pelvic inflammatory disease; abdominal pain; ectopic pregnancy; infertility; and perinatal infection.
Urethral syndrome
is a condition of uncertain aetiology that only affects women. It manifests as dysuria, frequency, and urgency without evidence of infection, although some cases improve with antibiotics.
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