Sterile pyuria is the presence of elevated numbers of white cells (>10 white cells/mm3) in urine which appears sterile using standard culture techniques.
- Sterile pyuria is not an uncommon laboratory finding.
- Sterile pyuria is often found in female patients with symptoms of urinary tract infection (UTI). 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 a recognised urinary pathogen.
- Fewer than 100,000 colony-forming units (cfu) per mL reported - eg, it may be that urine was diluted by high fluid intake or an 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.
- The presence of pyuria increases the significance of a low bacterial count in the urine.
- Cell count per high power field is inaccurate and use of a counting chamber or similar gives more accurate results.
- A recently (within preceding two weeks) treated urinary tract infection (UTI) or inadequately treated UTI.
- UTI with 'fastidious' organism (an organism that grows only in specially fortified artificial culture media under specific culture conditions) - eg, Neisseria gonorrhoeae.
- Renal tract tuberculosis.
- Chlamydial urethritis.
- False negative culture due to contamination with antiseptic.
- Contamination of the sample with vaginal leukocytes.
- Interstitial nephritis: sarcoidosis (lymphocytes not neutrophils).
- Urinary tract stones.
- Renal papillary necrosis: diabetes, sickle cell disease, analgesic nephropathy.
- Urinary tract neoplasm, including renal cancer and bladder cancer.
- Polycystic kidneys.
- Interstitial cystitis.
- Kawasaki disease.
- Other reported associations include appendicitis and systemic lupus erythematosus.
- Urinalysis: initial test to identify likely infection but a urine sample needs to be sent to the laboratory. See the separate article on Urine Dipstick Analysis. Positive nitrite test +/- positive leukocyte esterase test. Haematuria and proteinuria occur in UTI but are also present in other conditions.
- Urine microscopy, culture and sensitivities; ask the laboratory to culture under conditions allowing identification of fastidious or slow-growing organisms.
- Consider the possibility of sexually transmitted disease; take a sexual history and consider sending swabs for chlamydia and N. gonorrhoeae.
- Polymerase chain reaction (PCR) testing of sterile pyuria has been recommended for the detection of Chlamydia trachomatis, mycoplasma and ureaplasma infections.
- Always consider tuberculosis; culture for AFBs (three early morning urine samples).
- With urine obtained direct from the bladder, any organism grown is significant and should be treated with a prolonged course of appropriate antibiotics.
- Cystoscopy may be required to exclude non-infective causes.
- Management of any identified underlying cause.
Further reading and references
Dieter RS; Sterile pyuria: a differential diagnosis. Compr Ther. 2000 Fall26(3):150-2.
Daher Ede F, da Silva GB Jr, Barros EJ; Renal tuberculosis in the modern era. Am J Trop Med Hyg. 2013 Jan88(1):54-64. doi: 10.4269/ajtmh.2013.12-0413.
Singh S, Kansra S; Kawasaki disease. Natl Med J India. 2005 Jan-Feb18(1):20-4.
Nassar FA, Abu-Elamreen FH, Shubair ME, et al; Detection of Chlamydia trachomatis and Mycoplasma hominis, genitalium and Adv Med Sci. 200853(1):80-6.
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