oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
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 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.
Causes of sterile pyuria
- A recently (within last 2 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.
- Other reported associations include appendicitis, systemic lupus erythematosus and Kawasaki disease.
- Urinalysis: initial test to identify likely infection but a urine sample needs to be sent to the laboratory. See separate article Urine Dipstick Analysis. Positive nitrite test +/- positive leukocyte esterase test. Haematuria and proteinuria occur in urinary tract infection (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 (3 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 & references
- Dieter RS; Sterile pyuria: a differential diagnosis. Compr Ther. 2000 Fall;26(3):150-2.
- Tayal SC, Pattman RS; Sterile pyuria: consider chlamydial infection. Br J Clin Pract. 1996 Apr-May;50(3):166-7.
- Nassar FA, Abu-Elamreen FH, Shubair ME, et al; Detection of Chlamydia trachomatis and Mycoplasma hominis, genitalium and Adv Med Sci. 2008;53(1):80-6.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Colin Tidy
Dr Colin Tidy