A urine culture is a laboratory test that detects and identifies bacteria or yeast in a urine sample. Its purpose is to diagnose urinary tract infections (UTIs) by pinpointing the specific microorganism responsible. This diagnostic tool guides healthcare providers in selecting the most effective antibiotic treatment.
Preparing for Sample Collection
Proper preparation prevents contamination and ensures accurate results when collecting a urine sample. This prevents contamination from bacteria naturally present on the skin around the genital area. Patients should wash their hands thoroughly with soap and water before collection.
For females, separate the labia and cleanse the area from front to back with an antiseptic wipe. Males should wipe the head of the penis with an antiseptic towelette. If uncircumcised, pull back the foreskin before cleaning and keep it retracted during collection.
Collecting the Urine Sample
The “midstream clean-catch” technique is the most common method for collecting a urine sample. This minimizes external contamination. First, urinate a small amount into the toilet.
After the initial flow, place the sterile collection cup into the urine stream to collect the “midstream” portion. Fill the cup about halfway without touching the inside of the container or the genital area. Once enough urine is collected, pass the remaining urine into the toilet and securely tighten the lid on the cup.
What Happens in the Laboratory
Once the urine sample arrives at the laboratory, it is processed to determine the presence and type of microorganisms. A small amount of urine is spread onto specific culture media that provide nutrients for bacteria and fungi to grow. These plates are then incubated for 24 to 48 hours to allow any microorganisms to multiply and form visible colonies.
After incubation, laboratory technicians examine the plates for bacterial growth. The number of colonies is counted and reported as Colony Forming Units per milliliter (CFU/mL). If significant growth occurs, further tests identify the specific type of bacteria or yeast. Antibiotic susceptibility testing (AST) is also performed to determine which antibiotics are effective against the identified microorganism, guiding treatment.
Understanding Your Results
Interpreting urine culture results involves considering the number of bacteria, the specific type identified, and their susceptibility to antibiotics. For a clean-catch sample, a count of 100,000 CFU/mL or more of a single type of bacteria generally indicates an infection. Lower counts (1,000 to 100,000 CFU/mL) can still be significant if symptoms are present. If multiple types of bacteria are present without a predominant organism, it often suggests contamination during collection, necessitating a repeat test.
Common bacteria found in UTIs include the most frequent cause, Escherichia coli (E. coli), along with Klebsiella, Proteus, and Enterococcus species. The antibiotic susceptibility report classifies antibiotics as “susceptible,” “intermediate,” or “resistant.” “Susceptible” means the antibiotic is likely effective at standard doses. “Resistant” means the antibiotic will likely not be effective against the infection.