Diagnostics

Symptomatic, uncomplicated lower UTIs can be diagnosed clinically. In all other patients, urinalysis is the most important initial diagnostic test.

• Uncomplicated lower UTI in women

  • Typical symptoms : Treatment may be initiated without further diagnostics.

  • Atypical or unclear symptoms: Perform urinalysis using a urine dipstick test and/or microscopy.

    • Positive urinalysis (proof of pyuria and bacteriuria): Initiate treatment.

    • Negative urinalysis but persisting suspicion: Obtain urine culture.

• Complicated lower UTI in women

  • Obtain urinalysis and urine culture.

  • Consider the need for further diagnostics, depending on history and clinical presentation.

• Lower UTI in men

  • Obtain urinalysis and urine culture.

  • First febrile UTI: Perform CT or ultrasound of the urinary tract.

  • Consider referral to urology (e.g., in case of unclear diagnosis, hematuria, voiding difficulties, or recurrent UTI)

  • Concomitant prostatitis: See “Diagnostics” in “Prostatitis.”

• Upper UTI: See “Diagnostics” in “Pyelonephritis.”

UTI is primarily a clinical diagnosis that is supported by typical findings on urinalysis. Urine culture is indicated in select cases to determine the causative pathogen and adapt antibiotic treatment.

• Indications: best initial test for all patients

• Procedure: visual, chemical (dipstick), and microscopic examination of urine

• Specimen collection method

  • Clean-catch midstream sample: thought to reduce contamination with vaginal or skin flora

  • Straight catheterization of the bladder: may be considered if the risk of contamination is high

  • Suprapubic aspiration: no contamination if performed correctly but rarely used due to its invasive nature

• Typical urinalysis findings of UTI [9]

  • Pyuria: presence of white blood cells (WBCs) in the urine

    • Positive leukocyte esterase: an enzyme produced by WBC

    • ≥ 5 WBC/HPF or ≥ 8–10 WBC/mm3 [24][25]

  • Bacteriuria: presence of bacteria in the urine [26]

    • Positive urinary nitrites: indicate bacteria that convert nitrates to nitrites (most commonly gram-negative bacteria; e.g., E.coli)

    • Direct visualization by gram stain (seldom performed)

• Other findings

  • Leukocyte casts may indicate pyelonephritis.

  • Micro- or macroscopic hematuria may be present.

  • Alkaline urine (pH > 8) and struvite crystals in sediment: indicate urease-producing organisms (e.g., Proteus, Klebsiella, Staphylococcus saprophyticus) [19][27]

  • The presence of squamous epithelial cells can be a sign of contamination.

• Indications

  • Suspicion for complicated UTI or healthcare-associated UTI

  • Suspicion for pyelonephritis or urosepsis

  • Suspicion for uncomplicated cystitis with either of the following:

    • History of recurrent UTIs [10]

    • Equivocal urinalysis

    • Atypical symptoms

    • Concern for multiresistant pathogens, e.g., due to recent antibiotic use [15]

    • Age ≥ 65 years [28]

  • Follow-up cultures for test of cure in the following cases:

    • Nonresolving symptoms despite antibiotic treatment

    • Anatomic or functional abnormalities of the urinary tract

    • Continued pathological findings on urinalysis

• Interpretation

  • Cultures are considered positive if either of the following is present:

    • Significant bacteriuria: defined as ≥ 105CFU/mL in a clean-catch specimen [9][29]

    • Any organisms in a specimen obtained by suprapubic aspiration [24][30]

• Typical colony findings

  • E. coli: intensely pink on MacConkey agar

  • Klebsiella pneumoniae: viscous colonies

  • Serratia marcescens: often red in appearance

  • Proteus mirabilis: swarming motility pattern

  • Pseudomonas aeruginosa: blue-green pigment

• Pregnancy test: indicated in women of childbearing age

• Testing for sexually transmitted infections (STIs)

  • Indicated in patients with STI risk factors and/or symptoms of an STI

  • At-risk patients should be tested for Chlamydia trachomatis and Neisseria gonorrhoeae.

• Blood tests

  • Not routinely performed in patients with lower UTI

  • May be indicated to assess concomitant conditions (e.g., diabetes mellitus) and exclude differential diagnoses

Imaging is generally not indicated or helpful for the diagnosis of lower UTI, but it may be performed in select patients to rule out complicating factors (e.g., urinary tract obstruction) or if complicated pyelonephritis or urosepsis are suspected. For imaging indications and findings in upper UTI, see “Diagnostics” in “Pyelonephritis.”

• Indications may include:

  • Suspected urinary tract obstruction

  • Severe illness (e.g., septic shock)

  • Early recurrence of UTI (within two weeks of appropriate treatment)

  • Persistent bacteriuria despite treatment

  • Recurrent complicated UTI

  • Men with febrile UTI

• Modalities

  • CT abdomen and pelvis with or without IV contrast

    • Most sensitive for initial imaging

    • Noncontrast CT is useful to diagnose urolithiasis.

    • IV contrast is indicated if complications (e.g., abscess) or other causes of obstruction are suspected.

  • Ultrasound of the kidneys and bladder

    • Perform if there are contraindications to contrast or radiation.

    • Useful for detecting hydronephrosis and measuring postvoid residual volume if an obstruction is suspected

  • Additional modalities include MRI abdomen and pelvis, voiding cystourethrography, and retrograde cystography.

Imaging is not routinely necessary for patients with uncomplicated lower UTI.