Sterile Pyuria

Sterile pyuria is the presence of elevated numbers of white cells (>10/cubic mm) in a urine which appears sterile using standard culture techniques:

• Often found in female patients with symptoms of urinary tract infection and presence of pyuria but no bacterial growth can be cultured. However, these results may be misleading for various reasons:
  • Standard laboratory culture conditions may not be optimal for growth of atypical organisms.
  • Laboratory may not report significant growth either because it was not a single organism or recognised urinary pathogen.
  • Less than 100,000 colony-forming units per ml reported, e.g. may be urine was diluted by high fluid intake or organism may be slow growing. Studies have shown that approximately half of women presenting with symptoms and counts of 100 -10,000 cfu/ml have genuine bladder infections.
• Presence of pyuria increases significance of a low bacterial count.
• Cell count per high power field is inaccurate and use of counting chamber or similar gives more accurate results with 10 white cells/mm3 being diagnostic of infection.

• A recently (within last 2 weeks) treated UTI or inadequately treated UTI.
• UTI with 'fastidious' organism.
• Renal tract tuberculosis; Chlamydial urethritis.
• False negative culture due to contamination with antiseptic.
• Contamination of sample with vaginal leucocytes.
• Interstitial nephritis: analgesic nephropathy, sarcoidosis (lymphocytes not neutrophils).
• Urinary tract stones.
• Renal papillary necrosis: diabetes, sickle-cell disease, analgesic nephropathy.
• Urinary tract neoplasm.
• Polycystic kidneys.
• Interstitial cystitis .
• Prostatitis.
• Other reported associations include appendicitis, systemic lupus erythematosus and Kawasaki disease.

Common.¹

• UTI: severe dysuria, frequency, urgency, urge incontinence, haematuria, constant suprapubic discomfort, non-specific malaise.
• Interstitial cystitis: similar symptoms to UTI with sterile pyuria. Cystoscopy shows inflammation, sometimes with ulceration. May progress to cause contracture of the bladder. Cause is unknown.

• Ask laboratory to culture under conditions allowing identification of fastidious or slow growing organisms.
• Always consider TB: culture for AFB's (3 early morning urines).
• With urine obtained direct from the bladder, any organism grown is significant and should be treated with a prolonged course of appropriate antibiotics.
• Otherwise cystoscopy to exclude non-infective causes.

• Always consider TB or non-infective cause and don't prescribe antibiotics if infection not proven or otherwise suspected.
• Antibiotics as indicated by culture, can try blind trial of tetracycline for chlamydia.²