At a glance
Also known as
Urine MCS; urine microscopy & culture; urine culture & sensitivity; C&S
Why get tested?
A urine culture is used to diagnose a urinary tract infection UTI
When to get tested?
If you experience symptoms of a UTI, such as pain during urination.
A mid-stream "clean" urine sample; a "in-out" catheter urine sample; a suprapubic aspirate urine sample
What is being tested?
Urine is one of the body’s waste products. It is produced in the kidneys and collected in the bladder until a person urinates. Urine in the bladder is normally sterile (containing no organisms), however, if bacteria or yeasts are introduced into the urinary tract, they can multiply and casue a urinary tract infection (called a UTI). Bacteria are usally present around the opening of the urethra (the tube that leads from the bladder to the outside of the body). Urine collection for culture (MCS) must be performed carefully in order to avoid contaminating the sample with these bacteria.
Because urine itself can serve as a culture medium, any bacteria present, including contaminating microorganisms, will multiply rapidly if the urine sample is allowed to stand at room temperature. For this reason, urine samples should be refrigerated (at about 4°C) after collection and transported to the laboratory as soon as possible.
Uncomplicated urinary tract infections (UTIs or cystitis) mainly occur in non-pregnant women who do not have any abnormality of the urinary tract. Acute uncomplicated cystitis (bladder infection) and pyelonephritis (kidney infection) are most commonly caused by Escherichia coli (70 to 95% of cases) and Staphylococcus saprophyticus (5 to 10% of cases).
Complicated UTIs occur inpatients with underlying abnormalities of the urinary tract. E.coli is the most common pathologen (20 to 50% of cases), but a wider range of bacteria (eg Klebsiella, Proteus, Pseudomonas species) also cause infection. Symptomatic UTIs caused by yeasts such as Candida are uncommon.
UTIs in men are uncommon; although more likely to occur with increasing age and abnormalities of the urinary tract. Prostate infection (prostatitis) should be considered in men. Measuring the PSA level on a blood test may be useful.
How is the sample collected for testing?
A ‘mid-stream’ urine sample is the most common collection necessary for a in order that present around the urethra and on the hands are not introduced.
Guidelines for collection of mid-stream urine sample:
- Open the sterile urine jar and hold it in one hand. Sit on the toilet with your legs wide apart. Use the fingers of your other hand to hold your labia apart- the urine must not touch either your labia or your fingers. Starting passing the urine directly into the toilet. After a few seconds, catch your urine in the container. Once the container is half filled (20-30mls), screw the cap on tightly. DO NOT contaminate the urine with your fingers.
- Open the urine jar and hold it in one hand. If you are not circumcised, retract your foreskin. Start passing the urine directly into the toilet. After a few seconds, catch your urine in the container. Once the container is half filled, screw the cap on tightly. DO NOT contaminate the urine with your fingers.
REMEMBER: Do not collect the first portion of urine you pass.
- Hands should be washed before and after collection.
- Ensure the container is labelled with your name, date of birth and date of collection.
Uncontaminated specimens can also be obtained from people who are catheterised following the same hygienic procedures for the end of the catheter.
Other methods of collection require a health care worker to insert a catheter into the bladder (in-out catheter) or a needle into the bladder (suprapubic aspirate) and are more invasive for the person but may be necessary in people who are unable to collect a mid-stream urine and who do not have a catheter already in place.
How is the sample tested in the laboratory?
A sample of the urine is initially assessed under microscope or a cell counting instrument and visible cells are counted. The presence of large numbers of white blood cells (‘pus cells’) is strongly indicative of a UTI. The growth of mixed bacterial types on urine culture or the presence of large numbers of squamous epithelial cells (cells originating from the skin and not the bladder) on microscopy usually indicates a poorly collected specimen and contamination with normal genital tract flora.
A small amount of urine (usually 10 microlitres) is then cultured and on agar plates which are placed in an incubator for 24 hours. The culture is usually considered ‘negative’ if no significant growth is found on the plates after 24 hours. Occasionally cultures may be prolonged to look for unusual organisms.
If bacteria or yeasts are growing, the total number of organisms is counted (colony count), with the concentration of viable bacteria in a urine sample expressed as colony forming units per litre (CFU/L). UTI is usually defined as a bacteria count >108 CFU/L from a midstream urine sample. Lower bacterial counts (105 CFU/L or more) may also indicate UTI in women with symptoms, patients with a UTI caused by organisms other than Escherichia coli and Proteus species, men and patients already taking antibiotics.
Organisms are identified by growth characteristics, proteomic testing with and/or additional biochemical testing.
Further tests determine which antibiotics are likely to be effective in treating the infection (susceptibility tests).