Urine culture: how to collect a sample correctly and what an antibiogram means

Urine culture is a microbiological urine test showing whether urine contains a bacterium causing a urinary tract infection, which bacterium it is and which antibiotics it is susceptible to. Susceptibility is presented in an antibiogram, which helps the doctor choose a medicine. Reliability depends most on correct sample collection.

Who is this test for

• people with burning or pain during urination, frequent and urgent urination, pain above the pubic bone, cloudy urine or blood in urine,
• men, pregnant women and children with these symptoms, before starting antibiotics,
• people whose symptoms do not improve 48 hours after starting treatment or whose infections recur,
• pregnant women even without symptoms, when their gynaecologist considers it appropriate,
• people before certain urological procedures.

What urine culture shows

In the laboratory, urine is inoculated onto culture media. If bacteria are present, they grow into colonies that are counted and identified. The most common cause of urinary tract infections is the bacterium Escherichia coli.

Urinalysis (dipstick and sediment) quickly shows signs of inflammation and bacteria in urine, such as white blood cells and nitrites, while urine culture confirms infection, identifies the bacterium and tests it against antibiotics. Negative nitrites do not rule out infection.

Standard urine culture does not detect chlamydia, mycoplasmas, ureaplasmas or gonorrhoea. If burning during urination accompanies discharge, the doctor may recommend testing for sexually transmitted infections.

Seek medical attention immediately for fever, chills or flank pain, as these may be signs of a kidney infection.

How to collect a urine culture sample correctly

For urine culture, collect a midstream sample of the first morning urine into a sterile container after washing the genital area with water. Deliver it as soon as possible, preferably within 2 hours. Incorrectly collected samples may contain skin bacteria, and bacteria multiply in samples left standing, so the result may show an infection that is not present.

Before you start

• Container: a sterile screw-top container.
• Timing: the first morning urine is best because it has remained in the bladder overnight. If this is not possible, collect a sample after not urinating for at least four hours.
• Antibiotics: collect the sample before the first dose, because an antibiotic may produce a false-negative result. If you have already started taking it, mention this when submitting the sample.

Midstream collection, step by step

1. Wash your hands.
2. Wash the genital area with water only, without disinfectants or antiseptic wipes, because residues can stop bacterial growth. Women wash from front to back, while men retract the foreskin and wash the glans.
3. Open the container immediately before urinating and do not touch its interior.
4. Pass the first part of the stream into the toilet. This flushes bacteria out of the urethra.
5. Without interrupting the stream, collect the middle portion in the container, 20 to 30 ml, without filling it to the top. Women should separate the labia, while men keep the foreskin retracted.
6. Pass the remaining urine into the toilet. Close the container tightly and label it with your first name, surname, collection date and time.

Delivery to the laboratory

Deliver the sample as soon as possible, preferably within 2 hours, because bacteria multiply in urine left standing and the result may show more bacteria than were present in the bladder.

How urine culture results are interpreted

The report lists the bacteria found and, if necessary, an antibiogram.

• No bacterial growth: infection with common bacteria has not been demonstrated. If symptoms persist, the doctor investigates another cause.
• One bacterial species found: suggests infection, and the doctor assesses the result together with symptoms.
• Several bacterial species: most often means the sample is contaminated. A new, correctly collected sample is usually requested.

Bacteria in urine without symptoms (asymptomatic bacteriuria) are generally treated only during pregnancy and before urological procedures.

What an antibiogram means

An antibiogram is the part of the report showing which antibiotics the isolated bacterium is susceptible or resistant to. Each antibiotic is marked according to European EUCAST:

Category	Meaning
S – susceptible, standard dosing regimen	Treatment with a standard dose is very likely to succeed.
I – susceptible, increased exposure	The antibiotic works at a higher dose or when concentrated at the infection site, for example in urine.
R – resistant	Treatment with this antibiotic is unlikely to succeed.

Category I does not mean the antibiotic “works less well”: both S and I indicate susceptibility. However, an antibiogram is not a prescription. The doctor also selects the medicine according to allergies, pregnancy, kidney function and other medicines you take. If you are already taking an antibiotic and the report shows resistance to it, contact your doctor.

How to arrange testing

Poliklinika Analiza branches are located in Split, Zagreb, Zadar, Rijeka, Varaždin, Šibenik, Makarska and Dugopolje. Testing is available without a referral or appointment: you can submit a urine sample at any branch (listed on the page Contact). Prices for all tests and panels are on the service price list.

Urinalysis (dipstick and sediment) is often performed alongside urine culture. Urine culture takes longer than urinalysis because bacteria first need to grow, before being identified and tested against antibiotics. Take the results to the doctor who recommended the test.

Frequently asked questions

Can I provide a sample during menstruation?

It is better to wait until menstruation has ended, because blood may contaminate the sample. If your doctor requests immediate testing, mention that you are menstruating when submitting the sample.

Is a follow-up urine culture needed after treatment?

Usually not if symptoms have resolved. Exceptions include pregnant women and recurrent or complicated infections, when the doctor decides whether and when a follow-up is needed.

How is a urine culture sample collected in young children?

In children too, a midstream sample should be collected into a sterile container whenever possible. A sterile bag attached to the genital area more often produces a contaminated sample and must not remain in place for longer than an hour. Agree the collection method with the paediatrician.