What are the causes of sterile pyuria in a 70-year-old man with lower urinary‑tract symptoms?

Causes of Sterile Pyuria in a 70-Year-Old Male with LUTS

In a 70-year-old man with lower urinary tract symptoms, sterile pyuria is most commonly caused by benign prostatic obstruction with associated prostatic inflammation, though sexually transmitted infections (particularly Chlamydia trachomatis and Ureaplasma urealyticum) and genitourinary tuberculosis must be systematically excluded.

Primary Differential Diagnosis

Benign Prostatic Obstruction with Inflammation

• Prostatic inflammation is the leading cause of sterile pyuria in elderly men with LUTS, occurring in up to 70% of patients with pyuria and benign prostatic hyperplasia 1
• The inflammatory process within the prostate can cause leukocytes to appear in urine without bacterial growth on standard culture 1
• This inflammation may contribute to irritative voiding symptoms and decreased urinary flow, though the exact mechanism remains incompletely understood 2
• Digital rectal examination should specifically assess for prostatic tenderness, boggy consistency, or asymmetry that might suggest chronic prostatitis 3

Sexually Transmitted Infections

• Chlamydia trachomatis is detected in 10% of sterile pyuria cases and should be considered even in older men with new sexual partners 4
• Ureaplasma urealyticum accounts for 5% of sterile pyuria cases, with significantly higher prevalence in males 4
• Mycoplasma genitalium (1% prevalence) and Mycoplasma hominis (3% prevalence, primarily in females) are less common but important causes 4
• Standard urine cultures fail to detect these organisms; polymerase chain reaction (PCR) testing is required for diagnosis 4

Genitourinary Tuberculosis

• Must be excluded in patients with risk factors including prior tuberculosis exposure, immunosuppression, or endemic area residence
• Requires acid-fast bacilli testing and mycobacterial culture, which are not part of routine urinalysis

Essential Diagnostic Workup

Immediate Evaluation

• Measure post-void residual volume by bladder ultrasound, with volumes >300-500 mL requiring urgent catheterization 5
• Perform urinalysis to confirm pyuria (>10 leukocytes/high-power field) and document absence of nitrites and bacterial growth 4
• Obtain urine culture to definitively confirm sterility after 24-48 hours 4
• Complete digital rectal examination to assess prostate size, consistency, nodules, and tenderness 3

Specialized Testing Based on Clinical Context

• Order PCR testing for Chlamydia trachomatis, Ureaplasma urealyticum, and Mycoplasma species if the patient is sexually active or has urethral symptoms 4
• Consider mycobacterial culture if tuberculosis risk factors are present
• Uroflowmetry with at least 2 recordings (ideally >150 mL voided volume each) to assess maximum flow rate, with Qmax <10 mL/second suggesting obstruction 6
• Prostate-specific antigen (PSA) testing, recognizing that sterile pyuria itself can elevate PSA levels independent of malignancy 1

Management Algorithm

When STI Testing is Positive

• Treat according to current CDC guidelines for the identified organism
• Recheck urinalysis 2-4 weeks after completing antimicrobial therapy to confirm resolution of pyuria
• Screen and treat sexual partners to prevent reinfection 7

When Benign Prostatic Obstruction is Confirmed

• Initiate alpha-blocker monotherapy (tamsulosin 0.4 mg daily or alfuzosin) as first-line treatment for bothersome voiding symptoms 3
• Consider combination therapy with 5α-reductase inhibitor (finasteride 5 mg daily) if prostate volume >40 mL or PSA >1.5 ng/mL, which reduces acute urinary retention risk by 79% 5
• Reassess at 2-4 weeks after initiating alpha-blocker therapy using International Prostate Symptom Score (IPSS) 5
• Do not prescribe antimuscarinics without first measuring post-void residual, as these medications worsen incomplete emptying and increase retention risk 5, 8

When Tuberculosis is Confirmed

• Refer immediately to infectious disease for multi-drug antituberculous therapy
• Coordinate care with urology for management of any structural complications

Mandatory Urologic Referral Criteria

Refer immediately to urology before initiating treatment if any of the following are present 3, 8:

• Hematuria (microscopic or macroscopic)
• Abnormal PSA or digital rectal examination findings suspicious for prostate cancer
• Severe obstruction with Qmax <10 mL/second
• Elevated post-void residual (>150-200 mL)
• Recurrent urinary tract infections
• Renal insufficiency potentially due to obstructive uropathy
• Upper urinary tract dilatation on imaging
• Neurological disease affecting bladder function

Critical Pitfalls to Avoid

• Do not assume all pyuria represents bacterial UTI and reflexively prescribe antibiotics—this leads to substantial overtreatment, with 66% of patients receiving unnecessary antibiotics when STIs are the actual cause 9
• Do not rely on nitrite testing to guide antibiotic decisions in sterile pyuria—nitrite-positive urines are actually 18% more likely to be associated with negative cultures in STI-positive patients 9
• Do not overlook STI testing in older men based on age alone—sexual activity continues in this population and Chlamydia remains a significant cause 7, 4
• Do not delay urologic referral in elderly patients with severe obstruction, as complication risk increases dramatically with age 5
• Do not add antimuscarinics to the treatment regimen for LUTS with sterile pyuria, as they worsen urinary retention risk in elderly men with elevated baseline post-void residual 5, 8