- Culture & Sensitivity (Urine)
- C&S urine
- 5 mL urine in a disposable sterile plastic collection container or gray-top urine culture transport tube with preservative (provided by lab)
Additional information
- Use a freshly voided specimen
- Send specimen to lab immediately. If delayed, refrigerate the specimen within 30 minutes for use up to 24 hrs (do not freeze)
- Skin epithelium, bacteria, secretions, hair, lint, etc should not contaminate the sample
- Specimen should be properly labeled, including method and time of collection
- Specimen collected prior to antimicrobial therapy
- Early morning samples preferred
- Instructions for clean catch midstream urine collection:
- For male
- Thoroughly wash his hands
- Cleanse the meatus
- Void a small amount into the toilet
- Void directly into the specimen container
- For female
- Thoroughly wash her hands
- Cleanse the labia from front to back
- While keeping the labia separated, void a small amount into the toilet
- Without interrupting the urine stream, void directly into the specimen container
- Urine collection in children (<3 yrs):
- Catheterized specimen strongly recommended, however, if collection bag technique is utilized, use procedure below
- Cleanse the genital area and allow the area to dry
- Remove the covering over the adhesive strips on the collector bag and apply over the genital area. Diaper the child
- When specimen is obtained, place the entire collection bag in a sterile urine container
- Urine collection from indwelling catheter:
- Empty the drainage tube of urine and clamp it
- Cleanse specimen port with antiseptic swab, and then aspirate 5 mL of urine with a 21- to 25-gauge needle and syringe
- Transfer urine to a sterile container
- Urine collection by suprapubic aspiration:
- Instruct the patient to lie down in supine position
- Cleanse the area with antiseptic and drape with sterile drapes
- Insert a needle attached to a syringe, preferably guided by ultrasonography, approximately 2 cm above the symphysis pubis, aspirate the urine sample, and transfer to a sterile container
- The needle is removed and a sterile dressing is applied to the site
- Urine culture is performed to quantitate, isolate and identify a pathogenic microorganism in a patient's urine
- Sensitivity is performed following isolation of a pathogenic microorganism. Sensitivity testing specifies which antimicrobials the microorganism is sensitive or resistant to
- Urine is normally sterile and any growth of bacteria is abnormal
- Contamination can occur due to urine coming in contact with bacteria from the prostate, urethra or genitalia
- Urine is an excellent culture and growth medium at room temperature for most organisms that infect the urinary tract
- The clinical utility of urine culture and sensitivity test include:
- As an aid in the diagnosis of urinary tract infection
- To monitor for bacterial colonization after urinary catheter insertion
- For evaluation of persons suspected of having UTI along with positive leukocyte esterase and nitrate test, microscopic detection of >10 WBCs/µL and bacteria (>20/hpf) on urinalysis
- For periodic evaluation of persons at high risk of UTI
- To differentiate contamination of the urine sample by organisms outside the bladder from true infection
- As a screening test for asymptomatic bacteriuria during pregnancy (12-16 wks)
- To evaluate and determine susceptibility of isolated bacteria to antibiotics
- To monitor response to therapy for UTI
- Risk factors/Conditions related to developing a UTI:
- Previous leukocyte esterase and/or nitrate in urine
- Recurrent UTIs
- Pregnant women
- Children <3 yrs
- Diabetes mellitus
- Recent urological surgery or cystoscopy
- Neurogenic bladder
- Chronic renal disease
- Renal transplant
- Genitourinary disorders such as nephrolithiasis, bladder calculi, congenital abnormalities
- Treatment failure of complicated cystitis
- Organisms which commonly cause UTI include:
- Escherichia coli and other Enterobacteriaceae
- Enterococcus sp. (Including VRE)
- Klebsiella
- Proteus mirabilis
- Pseudomonas aeruginosa
- Staphylococcus aureus (Including MRSA)
- Staphylococcus saprophyticus
- M. tuberculosis (requires special culture media)
- Streptococci (beta-hemolytic, usually group B)
- Corynebacterium urealyticum
- C. albicans and other yeast
- Interpretation of urine culture:
- Growth of a single organism to >100,0000 colony-forming units (CFU)/mL from a clean voided urine in girls is indicative of urinary tract infection
- Growth of a single organism to >10,000 CFU/mL from a clean voided urine in boys is indicative of UTI
- Counts <100,000 CFU/mL may be significant depending on patient's age, sex, history, number of types of organisms present, method of specimen collection, and use of antibiotics
- Bacterial count <10,000 CFU/mL is considered significant in symptomatic patients, patients who have urological disorders or undergone urological procedures
- When the bacterial count is <1,000 CFU/mL from catheterization, suprapubic aspiration, cystoscopy, or during surgery, it is considered clinically significant
- Isolation of >2 bacterial species or of vaginal or skin organisms on culture is indicative of contamination during collection, and requires repeat culture with a fresh specimen
- Isolation of multiple organisms from a specimen collected in prolonged catheterization or urinary diversion (polymicrobial infection) should be interpreted cautiously
- A clean voided urine sample with negative bacterial growth, but a significant number of WBCs may indicate that the patient is on antibiotic therapy, may have tuberculosis infection, urinary calculi, epididymitis, urethritis, vaginitis, prostatitis or orchitis
- Common urethral contaminants include:
- Coagulase negative staphylococci
- Diptheroids
- Lactobaccilli
- Acid-fast Mycoplasma/Smegmatis
- Streptococci viridans
Additional information
- Although suprapubic catheterization and aspiration is superior to clean-catch or transurethral collection of bladder urine for bacteriologic study, it is rarely needed to correctly diagnose infection
- Isolation of Mycobacterium tuberculosis is performed only when specifically requested
- The diagnostic sensitivity of detecting UTI in females from a clean voided urine:
- Three specimens: 95%
- Two specimens: 90%
- One specimen: 80%
- 'Two glass test' is performed for urethritis with a recent history of sexually transmitted infection, where two urine samples are collected – the first 10 mL and a midstream sample. Significant bacterial growth in first sample is suggestive of urethritis, and is further tested for chlamydia and gonorrhea
- 'Stamey–Mears test' is performed to detect prostatitis. First, a clean-catch midstream urine sample is obtained and then, the client is instructed to stop passing urine, followed by prostatic massage per rectum, and 'expressed prostatic secretions' and final urine sample is then collected. If there is significant bacterial growth from the expressed prostatic secretions or the post-massage urine sample, then the midstream sample is indicative of prostatitis
- Localization test is performed to localize the site of infection to the bladder or to one or other kidney. The urine samples are obtained from each ureter and from the bladder during rigid cystoscopy
- 'Fairley test' is an alternate method to localize UTI
- Requires passage of a urethral catheter followed by a bladder washout with a wide spectrum antibacterial and a fibrinolytic enzyme
- Sequential urine samples are obtained
- If infection was present in the upper tracts, this will not have been affected by the bladder washout, and organisms will be detected in the first specimen obtained after washout, whereas, if infection was confined to the bladder, subsequent samples will be sterile
- Direct aspiration of urine under ultrasound guidance is helpful in UTI as a result of ureteric obstruction or renal cyst
- Factors interfering with test results include
- Fluid or drug induced diuresis may result in urine that is sufficiently dilute to reduce the bacterial count to <100,000 CFU/mL
- Antibiotic therapy initiated before specimen collection
- Bacterial contamination from vaginal secretions, vulva, or from the distal urethra in female patients, prepuce in male, perineal hair, hands, skin, or clothing
- Improper collection, storage and transport of urine specimen
- Urine collected from urine collection bag that is part of an indwelling catheter drainage system or bedpan
- Related laboratory tests include:
- BUN & Creatinine
- Gram stain
- Urinalysis
- White blood cell count
Culture: Negative/No growth
Method: Culture on selective and enriched media
- Positive: =105 organisms per mL urine
- Indeterminate: =104 organisms per mL urine
Positive result generally is >100,000 CFU/mL; however, lower numbers can be significant depending upon the clinical scenario and site of collection.
A negative culture result is quite sensitive, but false negatives may occur due to improper specimen handling, collection or antibiotics preceding collection of urinary specimen.
- Alper BS et al. Urinary tract infection in children. Am Fam Physician. 2005 Dec 15;72(12):2483-8. Available at URL: http://www.aafp.org/afp/20051215/2483.html
- Grover ML et al. Assessing adherence to evidence-based guidelines for the diagnosis and management of uncomplicated urinary tract infection. Mayo Clin Proc. 2007 Feb;82(2):181-5.
- Laboratory Corporation of America. Urine Culture, Comprehensive. [Homepage on the internet]©2007. Last accessed on March 6, 2007. Available at URL: http://www.labcorp.com/datasets/labcorp/html/chapter/mono/mb015550.htm
- LabTestsOnline®. Urine Culture. [Homepage on the Internet]© 2001-2006. Last reviewed on June 4, 2004. Last accessed on March 6, 2007. Available at URL: http://www.labtestsonline.org.uk/understanding/analytes/urine_culture/sample.html
- Mount SinaiHospital, Toronto. Urine Culture Manual. [Homepage on the internet]. Last reviewed on April 10, 2006. Last accessed on March 6, 2007. Available at URL: http://microbiology.mtsinai.on.ca/manual/urine/ur01.pdf
- Ontario Association of Medical Laboratories. Guidelines For Clinical Laboratory Practice: Indications for Urine Culture. [Homepage on the internet]©2001. Last reviewed in May 2004. Last accessed on March 6, 2007. Available at URL: http://www.oaml.com/PDF/CLP022.pdf
- OreskovicNM et al. Repeat urine cultures in children who are admitted with urinary tract infections. Pediatrics. 2007 Feb;119(2):e325-9.
- Travieso RF et al. Evaluation of the DIRAMIC system for detection of urinary tract infections and for Escherichia coli identification. Rev Latinoam Microbiol. 2004 Jul-Dec;46(3-4):67-71.
- U.S. Preventive Services Task Force. Screening for Asymptomatic Bacteriuria: Recommendation Statement. February 2004. Agency for Healthcare Research and Quality, Rockville, MD.Last accessed on March 6, 2007. Available at URL: http://www.ahrq.gov/clinic/3rduspstf/asymbac/asymbacrs.htm
- UTMB Laboratory Survival Guide®. URINE CULTURE. [Homepage on the Internet]© 2006. Last reviewed on September 6, 2006. Last accessed on March 6, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/micro/URINE%20CULTURE.html