Urine culture test: what it is, what it is for, and how long it takes

You have been ordered a urine culture test, and you want to understand what this test is, what it looks for, and when the answer will be ready. Here is the practical part: why a culture is needed, how it differs from a routine urine test, and which signs should not wait for the laboratory.

Urine culture test: what it is

A culture, also called a urine culture test, is a laboratory method. A urine sample is applied to a nutrient medium and the microorganisms are allowed to grow. Then the growth is studied: colonies of different species differ in size, shape, color, consistency, edge, and structure. By these features and by biochemical properties, the laboratory determines which bacteria are present in the urine. If there are few microorganisms in the sample, the culture is done on liquid enrichment media; if there are many, it is done on solid media to obtain isolated colonies. The unit of growth is the colony-forming unit, CFU: one such unit grows into one visible colony.

Why a urine culture is ordered, including for cystitis, and when to see a doctor

Urinary tract infections are the second most common infections in the body. They are usually caused by bacteria from the intestine: they enter the urinary tract through the urethra. In women it is shorter, so bacteria can more easily reach the bladder and kidneys, and women with such infections are about four times more numerous than men. In cystitis, that is, a bladder infection, the culture shows which flora grew and how much of it. A urine test is not always ordered for this.

Reasons to talk to a doctor:

• pain or burning during urination;
• urges more often than usual, including at night, or sudden and very strong urges;
• cloudy urine, blood in the urine, dark color, or a strong odor;
• pain in the lower abdomen or in the lower back under the ribs;
• high temperature, chills, weakness.

You need to make an urgent appointment if you are 65 years old or older, if this concerns a child under 15 years old, if you are a man, if you have diabetes, a weakened immune system, a catheter, or pregnancy. Also — if the temperature is very high or has dropped below 36 °C, if the symptoms worsen sharply or do not go away within 48 hours, if the infections recur: two in six months or three in a year.

Being ordered a culture is not in itself a reason to call an ambulance. 103 or 112 are needed if, against the background of a urinary tract infection, the person is confused, drowsy, or has difficulty speaking: such signs occur with a severe complication — a kidney infection with a risk of sepsis.

What a culture detects: bacteriuria, E. coli, and other flora

A culture answers the question of who exactly grew. Bacteriuria is the presence of bacteria in the urine, and it can be asymptomatic. E. coli is a common intestinal inhabitant that, once it enters the urinary tract, causes infection. In addition to it, the laboratory can isolate other microorganisms and count their number in CFU. Growth is assessed on both solid and liquid media: in liquid, some cultures produce uniform turbidity, others produce sediment at the bottom or a film on the surface.

How a culture differs from a general urine test

A general urine test is a chemical and microscopic examination. It shows, for example, nitrites, leukocyte esterase, epithelial cells, and mucus, but it does not grow or identify microorganisms. A culture is a cultural method: it grows microorganisms and allows them to be identified. In chronic urinary tract infections, routine urine tests do not always detect the causative agent, and then the result diverges from the symptoms.

How long a urine culture takes and how to read the result

A culture is never instant. First, the microorganisms need time to grow on the nutrient medium, then the laboratory studies the colonies and their properties. The result states whether there is growth, which microorganism was isolated, and how much of it there is — in CFU. The result is assessed by a doctor together with the symptoms.

How much urine is needed for the test and when a culture is ordered for men

The volume of the sample is clarified where you have the test done. Urinary tract infections in men occur about four times less often than in women, but a man with suspected such an infection needs to see a doctor urgently. The causes are sometimes related to difficulty emptying the bladder, for example an enlarged prostate.

This material is for reference: it explains what happens to your sample in the laboratory, but it does not replace a doctor's consultation — it is the doctor who interprets the form and plans the next steps.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer