You are here: Urology Textbook > Surgical management > Urinary tract infections > Diagnostic workup

Diagnosis of Urinary Tract Infection: Laboratory Tests and Imaging

• Urinary tract infection: definition and epidemiology
• Urinary tract infection: causes and risk factors
• Urinary tract infection: Diagnostic Workup
• Urinary tract infection: prevention and antibiotic treatment

Review literature: (Krieger, 2002) (Nickel, 2005a) (Nickel, 2005b) (Sussman and Gally, 1999) (Wagenlehner and Naber, 2006) (DGU 2009, S3-guideline for UTI).

Laboratory Tests in Urinary Tract Infections

Collection of specimen

The first choice for urine collection is sterile bladder catheterizations, during interventions or by suprapubic bladder puncture. Otherwise, the urine collection is made by a midstream clean-catch specimen or adhesive bag in infants. The risk of bacterial contamination is as high as 40% with noninvasive urine collection, depending on sex, age, and compliance.

Urine Sediment or Urine Dipstick Test:

In a urine analysis, signs of urinary tract infections are leucocyturia, (micro-) hematuria and bacteriuria (nitrite positive). The diagnostic value is low after prolonged catheterization.

Urine Culture:

After sterile urinary bladder puncture or single catheterization, any detection of bacteria in the specimen is considered pathological. Midstream urine specimens have a significant risk of contamination; the first hints are the detection of dermal or mixed flora. To further differentiate between contamination and significant bacteriuria, a quantitative urine culture with a bacterial count is used:

Quantitative urine culture:

10⁵ colony-forming units (CFU/ml) in midstream urine specimens indicate a UTI (Kass, 2002). Increased diuresis or pollakiuria results in a shorter urine passage time and can result in false-low bacterial counts in existing UTIs. 1000–100000 CFU/ml may already be clinically relevant if typical symptoms are present and common uropathogens without mixed bacterial growth are detected.

Blood tests:

In urinary tract infection with fever: blood count, CRP, Kreatinin. Blood cultures should be collected in case of high fever or signs of systemic infection (SIRS). See section urosepsis for further tests to identify complications of sepsis in severe urinary tract infection.

Basic Diagnostic Workup for Recurrent UTIs:

Ultrasound Imaging:

• Postvoid residual urine?
• Upper urinary tract obstruction?
• Nephrolithiasis?
• Diverticula of the bladder?
• Bladder stones?
• Ureterocele?
• Prostate adenoma?

Cystoscopy:

Perform cystoscopy only in an infection-free interval to exclude subvesical obstruction, diverticulum, bladder stones or bladder tumors. Take biopsies from suspicious lesions. According to the German guideline, routine cystoscopy is not indicated in women without other relevant comorbidities with recurrent urinary tract infections. This is understandable in young women without a high risk of bladder cancer. Cystoscopy should be recommended after a certain age (>50 years?), and if risk factors are present, see section hematurie.

Extended Diagnostic Workup for Recurrent UTIs:

Perform additional tests in case of abnormalities in the basic diagnostic workup.

Urinary Flow:

The measurement of urinary flow may identify subvesical obstruction or bladder emptying disorders.

Intravenous Urography or Computed Tomography:

To detect hydronephrosis, urinary stones, bladder diverticula, and anatomical malformations. The CT is superior to intravenous urography: it provides better imaging of anatomical details (cause of hydronephrosis?) and higher sensitivity to diagnose comorbidities.

Voiding cystourethrography:

Voiding cystourethrography is indicated if vesicoureteral reflux or bladder diverticulum is suspected.

Retrograde Urethrography in Men:

Retrograde urethrography if a urethral stricture is seen in cystoscopy or for suspected urethral diverticulum.

Radionuclide Studies:

DMSA scintigraphy allows the identification of renal scars and loss of function in vesicoureteral reflux.

Urodynamics:

Urodynamic studies in an infection-free interval help to classify suspected neurogenic lower urinary tract dysfunction.

References

Kass 2002 KASS, E. H.: Asymptomatic infections of the urinary tract. 1956.
In: J Urol
167 (2002), Nr. 2 Pt 2, S. 1016–9; discussion 1019–21

Krieger 2002 KRIEGER, J. N.: Urinary tract infections: what’s new?
In: J Urol
168 (2002), Nr. 6, S. 2351–8

Nickel 2005a NICKEL, J. C.: Management of urinary tract infections: historical perspective and current strategies: Part 1–Before antibiotics.
In: J Urol
173 (2005), Nr. 1, S. 21–6

Nickel 2005b NICKEL, J. C.: Management of urinary tract infections: historical perspective and current strategies: Part 2-Modern management.
In: J Urol
173 (2005), Nr. 1, S. 27–32

Sobel und Vazquez 1999 SOBEL, J. D. ; VAZQUEZ, J. A.: Fungal infections of the urinary tract.
In: World J Urol
17 (1999), Nr. 6, S. 410–4

Sussman und Gally 1999 SUSSMAN, M. ; GALLY, D. L.: The biology of cystitis: host and bacterial factors.
In: Annu Rev Med
50 (1999), S. 149–58

Wagenlehner und Naber 2006 WAGENLEHNER, F. M. ; NABER, K. G.: Treatment of bacterial urinary tract infections: presence and future.
In: Eur Urol
49 (2006), Nr. 2, S. 235–44

  Deutsche Version: Diagnostik und Bildgebung bei Harnwegsinfektion