Urine culture: What is it?  Why and how is it done?

Urine culture: What is it? Why and how is it done?

Urine culture it is a microbiological examination aimed at finding details microorganisms in urine. This analysis is indicated in case of suspected urinary tract infection (in particular, cystitis), as it allows the identification of any microorganisms implicated in the pathological process and their quantification.The main purpose of urine culture is diagnostic, but, if performed in association with antibiogram can prove useful in choosing the most suitable drug for eradicating the pathogen in question.

Why It Is Done

Normally, urine culture does not show significant concentrations of bacteria, since urine is generally sterile; only a rather small bacterial microflora colonizes the terminal part of the male urethra, while it is generally absent in the female one. Despite this, urinary tract infections (UTI) represent a pathological form frequently encountered in clinical practice.

The infection can come from other organs: in women, for example, from the vagina or anal area, in men from the prostate (in the presence of concomitant prostatitis).

What Is Urine Culture Used For?

Urine culture is a diagnostic test aimed at searching for microorganisms if there is an infection of the urinary tract (urethra, urinary bladder, renal pelvis or kidney) or of the genital system. Once collected, the urine sample is sent to the laboratory to be inseminated for culture which will allow the isolation and identification of the pathogen implicated in the clinical picture. The interpretation of the urine culture allows you to set the most appropriate therapeutic protocol for resolving the infection.

Urine Tests And Urine Cultures: When Are These Tests Prescribed?

Urine culture is ordered when a urinary tract infection causing discomfort and pain during urination, frequent need to urinate, and for all or some of the following symptoms is suspected:

  • General sense of malaise;
  • Sensation of not having completely emptied the bladder;
  • Burning or discomfort when urinating;
  • Cloudy, smelly urine;
  • Pain in the lower abdomen.

It should be considered, however, that the symptoms associated with a high level of pathogens in the urine can be non-specific and common to a large number of disorders and/or pathologies: consulting a doctor is, therefore, always indicated for the correct interpretation of the urine culture. .

Urine culture can also be performed in asymptomatic patients, for example if a previous urinalysis shows signs of an infection (alkaline pH, positive nitrites and leukocyturia, i.e. numerous white blood cells in the urinary sediment).

Urine culture is often performed during pregnancy, a period in which the woman is particularly exposed to the risk of urinary tract infections (often asymptomatic); the gynecologist will then be able to ask the pregnant woman to carry out a urine culture every thirty days, prescribing the most appropriate treatment whenever it is positive.

Urine Culture With Antibiogram

In the case of bacterial infections, urine culture allows evaluation, thanks to a antibiogram, the sensitivity or resistance of the infectious agent to antibiotics. It thus becomes possible to choose the most suitable antibiotic drug for the case, in order to determine the most suitable treatment and prevent the spread of resistant bacterial species.

The bacterium most frequently identified in urine is Escherichia coli.

Read also
Urine culture with Antibiogram: what does it consist of? When is it performed?

Normal Values

Urine is normally a sterile biological liquid or, at least, with a low bacterial load, therefore urine culture must give negative outcome.

Normal values:  less than 100,000 CFU (Colony Forming Units, i.e. bacteria) per milliliter.A urine culture in which there are from 10,000 to 100,000 CFU/ml is considered doubtful while the exam results positive when more than 100,000 CFU/ml are present. The confirmation of this last finding (positive urine culture) is a probable indicator of acute or chronic urinary tract infections (UTI).

In people with catheters, any burden is considered noteworthy, as this device facilitates the entry of bacteria and the onset of infections. Even if bacterial agents are found in the urine taken from the bladder (percutaneously using a sterile needle), the sample with a lower bacterial concentration is also considered positive. This finding indicates that there is inflammation supported by bacteria along the urinary tract, or, more rarely, pathogens from the blood are eliminated through the kidney.

How You Do It

Urine Culture: Preparation For Testing And Sample Collection

In the presence of urinary tract infections, urine culture represents a very useful diagnostic tool. Precisely in consideration of the purpose of the culture test (research and isolation of microorganisms), it is essential that the sample is not contaminated with germs coming from outside.

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Urine Collection – Practical Rules

Let’s see some simple rules to avoid this type of contamination.

  • Suspend, according to medical indications, any antibiotic and antifungal therapies in the 48 hours before the exam.
  • In the morning, before urinating, wash your hands and external genitals thoroughly with soap and water, rinsing for a long time with water; do not use disinfectants. In males, cleaning must take place after having completely retracted the skin of the foreskin; the woman will instead have to clean – preferably with gauze soaked in physiological solution and with movements from front to back – the internal surface of the labia majora and minora, parting the latter with her fingers before starting to urinate.
  • The sample collection must take place on the morning of the day of delivery of the exam, collecting the urine at least two hours after the last urination.
  • Begin urinating by discarding the first stream. Hold the urine and open the sterile container previously received in the laboratory or pharmacy.
  • Resume urinating into the sterile container, filling it just under half. Try not to wet the edges of the container or contaminate them with your hands, hair, genitals or underwear. Even more important is to avoid touching the inside of the container. NOTES: never open the sterile container before use.
  • Screw the lid back on immediately after urinating; make sure that the operation has been carried out correctly so as not to spill urine during transport.
  • If similar containers are used for urinalysis and urine culture, indicate which contains the first stream (valid for urinalysis) and which contains the subsequent one (valid for urine culture).
  • Bring the urine sample to the laboratory as soon as possible or store it at 4°C (in the refrigerator) for up to 12 hours. During transportation, be careful not to tip it over.

PLEASE NOTE: the indications provided by the reference analysis laboratory may vary slightly from those described. In pediatric age, for example, the urine culture sample is collected in a special sterile and adhesive plastic bag.

Interpretation Of Results

The results of the culture examination must be evaluated together with the results of the complete urinalysis by the general practitioner, who knows the medical history of his patient. Since some urine specimens can potentially be contaminated by normal skin bacterial flora, great care must be taken when interpreting the test.

If numerous bacteria are found in the urine, the doctor will prescribe antibiotic therapy, active against the type of bacteria identified as responsible for the infection, and will schedule subsequent checks to verify the effectiveness of the drugs taken.

To know more:
Positive urine culture: what it means and what to do?

Urine Culture With Antibiogram: Indications For Antibiotic Therapy

Once the response from the urine culture and antibiogram has been received, the doctor will choose the most suitable drug and recommend the daily frequency and duration of therapy. If an antibiotic treatment is prescribed, this must not be interrupted at the first disappearance or attenuation of the symptoms, but continued for the entire required period: this precaution limits the risk of relapses and the spread of antibiotic resistance.

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