Urinalysis Findings in Urethritis versus Cystitis
The key distinction is that urethritis typically shows pyuria (≥10 WBCs per high-power field) with negative nitrites and often negative leukocyte esterase, while cystitis commonly shows pyuria with positive nitrites and positive leukocyte esterase, though both conditions fundamentally present with genitourinary inflammation that cannot be reliably distinguished by UA alone. 1, 2
Urethritis UA Findings
Urethritis presents with specific urinalysis patterns:
Pyuria is present (≥10 white blood cells per high-power field on first-void urine or ≥2 WBCs per oil immersion field on Gram stain of urethral secretions), but this reflects urethral inflammation rather than bladder infection 2
Nitrites are typically negative because urethral pathogens (Neisseria gonorrhoeae, Chlamydia trachomatis, Mycoplasma genitalium, Trichomonas vaginalis) do not reduce nitrates to nitrites like typical uropathogens 1, 2
Leukocyte esterase may be positive or negative, as it detects WBCs but doesn't distinguish their source (urethra vs bladder) 2, 3
Bacteriuria is often absent or minimal on microscopy, as urethral pathogens don't colonize urine in the same manner as bladder infections 3
Cystitis UA Findings
Cystitis demonstrates a different urinalysis pattern:
Pyuria is present with evidence of bladder inflammation 1
Nitrites are frequently positive (though not always), as typical uropathogens like E. coli convert urinary nitrates to nitrites; nitrites have high specificity for bacterial cystitis 4, 5
Leukocyte esterase is typically positive, indicating significant pyuria from bladder inflammation 4, 3
Bacteriuria is commonly present on microscopic examination, with visible bacteria suggesting bladder colonization 4, 6
Critical Diagnostic Limitations
The diagnostic value of UA for distinguishing these conditions is fundamentally limited:
Pyuria alone cannot differentiate urethritis from cystitis because it indicates genitourinary inflammation from many causes, with exceedingly low positive predictive value for specific infection location 1, 7
The absence of pyuria effectively rules out both conditions in most patient populations, making it more useful as a negative predictor 1, 7
Clinical symptoms must guide diagnosis, not UA findings alone; urethritis presents with mucopurulent discharge and urethral discomfort, while cystitis presents with urgency, frequency, and suprapubic pain 1, 2
Practical Clinical Approach
Use this algorithmic approach:
First-void urine is essential for urethritis evaluation (captures urethral cells and pathogens), while midstream clean-catch is standard for cystitis 2, 3
In patients with dysuria plus urethral discharge or urethral discomfort, suspect urethritis regardless of UA findings and obtain nucleic acid amplification testing for gonorrhea and chlamydia 1, 2
In patients with dysuria plus urgency, frequency, and suprapubic pain without vaginal discharge, suspect cystitis; UA showing positive nitrites strongly supports this diagnosis 1, 7, 4
Negative nitrites do not rule out cystitis, as only 45-60% of uropathogens produce nitrites, and urine must be in the bladder for 4+ hours for conversion to occur 4
Common Pitfalls to Avoid
Critical errors in interpretation:
Do not equate pyuria with UTI or cystitis—it can represent urethritis, vaginitis, or other non-infectious inflammation 1, 3
Do not rely on UA alone for diagnosis; clinical symptoms are paramount, and evidence-based diagnosis should be primarily symptom-based with UA as adjunctive information only 1, 7
Do not assume negative leukocyte esterase rules out urethritis, as sensitivity varies and urethral inflammation may not produce sufficient WBCs in voided urine 2, 3
In sexually active patients with dysuria and pyuria but negative nitrites, strongly consider urethritis and test for sexually transmitted infections rather than treating empirically for cystitis 1, 2, 3