UTI Testing - How to Interpret Your Urinalysis and Culture

What is a urinalysis? Why do I have to wait for my urine culture? What are speciation and sensitivities?

Urinary tract infection (UTI) testing involves several steps ensure proper treatment and avoid unnecessary antibiotic use.
Urinalysis: This is a non-invasive chemical strip test that suggests whether urine is normal or abnormal. A completely negative urinalysis means no culture is required. It can identify three things relevant to infection: Leukocyte Esterase, which suggests inflammation in the urine, including UTI. Nitrites are present in the setting of certain types of bacteria. Blood sometimes indicates a UTI. Protein in the urine, especially on repeat testing, may indicate a kidney issue. Glucose suggests your blood sugar is over 160. Ketones are elevated when it's been a while since you have eaten and your body is absorbing fat or in certain circumstances with diabetes. Urine pH indicates your body's acid base balance related to normal diet changes, certain infections, and certain health conditions. Specific gravity typically shows how hydrated you are. Bilirubin may indicate something is going on with the liver or bile ducts. It should never be present. Urobilinogen is normally present in small amounts. When out of range, it may indicate something going on with the liver, red blood cells, bile duct, or recent antibiotic use.
The urine microscopy is really important to follow up certain abnormal urinalysis. It can assess more definitively the presence of red blood cells, white blood cells (pus), bacteria, or epithelial cells.
Urine Culture: This is the standard for confirming infections and identifying specific bacteria. It takes 48 to 72 hours to identify the bacteria and determine effective antibiotics. The speciation tells us what kind of bacteria are present and the susceptibilities which kinds of antibiotics can work.
PCR Urine Testing: While highly sensitive, PCR cannot distinguish between live bacteria causing infection and dead debris or harmless healthy bacteria. It is currently not considered the standard of care due to the risk of over-prescribing heavy antibiotics.
Importance of Proper Collection
Mid-stream Samples: To minimize contamination from the skin, patients are instructed to retract the vulva or foreskin and cleanse before catching a mid-stream sample.
Indwelling Catheters: For patients with a catheter, the most accurate sample is taken after changing to a new, sterile tube rather than from an old drainage bag.
Treatment of UTI (Antibiotic Stewardship) and Waiting for Results: Whenever possible, healthcare teams prefer waiting for final culture results before prescribing antibiotics to prevent resistance and ensure the selected drug is effective.
Empiric Antibiotics: In cases where a patient is severely symptomatic or at risk for sepsis, "empiric" antibiotics may be started while waiting for final lab results.
Avoiding Self-Medication: Taking leftover antibiotics at home before a lab test can lead to inaccurately negative cultures and is strongly discouraged.
Understanding Results
Colony Counts: A diagnosis of UTI is most certain when there are more than 100,000 colony-forming units (cfu) of a single bacterial type per milliliter. Lower colony counts can be relevant depending on symptoms and the situation.
Negative Cultures: Up to half of presumed UTIs may actually be negative cultures, meaning symptoms were due to something other than an infection. See our video on this!
Common Organisms: E. coli and Klebsiella are the most frequent causes of UTIs. Other bacteria may be considered contaminants or "innocent colonizers" depending on the patient's specific health context. More rarely, they may actually represent an infection.