Urinalysis vs. Urine Culture
If you’ve had a urinary tract infection (UTI), you’ve probably given a urine sample and waited to hear what it showed. Sometimes the results don’t match what you’re feeling. The test comes back negative while your symptoms continue, or the report is full of terms like “mixed flora” or “no significant growth.” Knowing what each test measures can help you make sense of your results and know what to ask your doctor next.
The two tests answer different questions. A urinalysis asks whether something looks wrong. A urine culture asks what is growing.
Table 1: Urinalysis vs. urine culture
| Feature | Urinalysis | Urine culture |
|---|---|---|
| What it looks for | Signs that your body is responding to infection or inflammation | Bacteria and in some cases fungi, but limited |
| How it works | A chemical test strip, and when done in a laboratory, laboratory instruments and a microscope | Urine is spread on petri dishes containing nutrients and incubated until microbes grow |
| Where it’s done | At-home (dipstick), in-clinic (dipstick), or in a lab | Laboratory only |
| Time to results | Minutes for a dipstick. Hours in a hospital lab. Usually 1-2+ days when sent to an outside lab. | 2-5 days when sent from a doctor’s office |
| Identifies the organism | No | Yes, for microbes that grow under the laboratory’s conditions |
| Tests which antibiotics work | No | No, requires antibiotic susceptibility testing following urine culture |
| Most useful for | Ruling out a UTI1 | Finding the cause of an infection for pathogens that grow in standard culture |
| Main limitation | Can’t tell you what is causing an infection, is often unreliable, and positive results require confirmation1 | Can miss microbes that don’t grow under standard laboratory conditions or are below laboratory reporting thresholds23, misses infections with multiple pathogens |
What is urinalysis?
Urinalysis is a type of diagnostic test that looks at the physical, chemical, and microscopic properties of urine. It can be used to assess kidney function, monitor diabetes, and help diagnose UTIs. For UTIs, urinalysis looks for signs of infection and inflammation in urine. It shows whether an infection is likely, but it doesn’t identify the specific pathogen. That’s why it is often the first test a provider orders. The exact markers checked vary from test to test. Two types of urinalysis are commonly used, and the technology behind them is what sets them apart.
The first type is the urine dipstick. Dipsticks are sold over-the-counter at pharmacies and are also used in doctors’ offices. They work by dipping a test strip into a urine sample, then comparing the color of each pad on the strip to a reference chart, either by eye or with a reader device during a healthcare visit. The second type is a laboratory urinalysis. Labs often use the same kind of chemical test strip, but read it with an automated instrument instead of by eye. They can also examine the urine under a microscope, which a dipstick can’t do. Results from either test can help a provider decide whether a urine culture is needed to identify what is causing an infection.
What does urinalysis detect?
When diagnosing UTIs, urinalysis looks for physical, chemical, or microscopic properties of urine that suggest infection or inflammation. When a pathogen is present in the urinary tract, the body’s immune system responds in a number of ways. Not every urinalysis checks for all of them.
Physical properties
Physical properties of urine that may suggest a UTI include:
- Color: Normal urine is typically pale yellow. A deep amber color often just means urine is concentrated. A red or pink tint can come from blood, but also from certain foods and medications. Color alone can’t tell you whether an infection is likely.
- Turbidity: Turbidity describes how cloudy or hazy a liquid is. Healthy urine is usually clear. Cloudy urine can mean white blood cells, bacteria, or mucus are present, but it is often caused by harmless crystals4. Turbidity is judged by eye or by a laboratory instrument.
- Odor: Odor isn’t measured as part of a urinalysis, but patients and providers often notice it. A strong smell is an unreliable sign of infection, since concentrated urine can smell strong too4.
Chemical properties
Chemical properties of urine that may suggest a UTI include:
- Leukocyte esterase: Leukocyte esterase is an enzyme that is produced by white blood cells. When it is found in urine, it suggests that the body’s immune system may be responding to a potential threat in the urinary tract.
- Nitrites: Many common UTI bacteria, including E. coli, convert nitrate from your diet into nitrite. A positive result suggests these bacteria are present. The conversion takes time, so urine that hasn’t been in the bladder long can test negative. Some UTI-causing organisms, such as Enterococcus and Candida, don’t produce nitrite at all. A negative nitrite result doesn’t rule out infection.
- Blood: The blood pad on a dipstick reacts to hemoglobin, the protein in red blood cells that carries oxygen. Blood in urine can come from irritation of the urinary tract lining during an infection, but it has many other causes, including menstruation and kidney stones.
- pH: The acidity of urine (pH) is also measured. Healthy urine is usually slightly acidic. Some uropathogens, such as Proteus mirabilis, produce an enzyme called urease that makes urine more alkaline. An alkaline result alone isn’t a sign of infection, since diet and a sample left sitting at room temperature can also raise pH.
Microscopic properties
Microscopic properties of urine are only examined when urinalysis is performed in a laboratory. A complete urinalysis always includes a microscopic exam. Some routine orders only add it when the chemical results are abnormal. Key markers include:
- White blood cells (WBCs): The laboratory counts white blood cells per “high-power field” (HPF), the area seen under the microscope at high magnification. More than 5-10 WBCs/HPF is considered pyuria, the main microscopic marker for UTI.
- Red blood cells (RBCs): Red blood cells are counted the same way. The presence of red blood cells in urine is called hematuria. It suggests that the lining of the urinary tract is irritated or damaged, though like a positive blood result on a dipstick, it has many possible causes.
- Squamous epithelial cells: Squamous epithelial cells line the skin and the outer parts of the urethra and vagina. Finding many of them suggests the sample picked up cells and microbes from outside the urinary tract during collection, which affects how the laboratory interprets any bacteria it finds. They are different from urothelial cells, which line the bladder and much of the urinary tract.
- Bacteria and fungi: The laboratory also looks for rod-shaped or round bacterial cells and oval-shaped yeast cells. Finding them can point to infection, colonization, or a contaminated sample. Microscopy can’t identify which bacteria or fungi are present. This is where urine culture comes in.
Table 2: Urine dipstick vs. laboratory urinalysis for UTI
| Feature | At-home dipstick | Clinic dipstick | Laboratory urinalysis |
|---|---|---|---|
| How you get it | Pharmacy or online, no prescription | During a visit with a provider | Ordered by a provider |
| Time to results | Minutes | Minutes | Hours in a hospital lab. Usually 1-2+ days when sent to an outside lab. |
| Who reads it | Patient, by matching colors | Clinic staff, by matching colors or using a reader device | Laboratory instrument and laboratory technician |
| Accuracy for UTI | Reasonable for ruling out a UTI when leukocyte esterase and nitrites are both negative. Weak for confirming one.1 | Reasonable for ruling out a UTI when leukocyte esterase and nitrites are both negative. Weak for confirming one.1 | Adds a microscopic exam and automated reading, but can’t confirm a UTI on its own |
| Physical properties | None. You may notice color or cloudiness yourself. | Color and clarity, if noted by clinic staff | Color and clarity |
| Chemical properties | Leukocyte esterase and nitrites (some add pH) | Leukocyte esterase, nitrites, blood, protein, pH, specific gravity, glucose, and more | Same as a clinic dipstick, usually read by an automated instrument |
| Microscopic properties | None. | None. | White and red blood cells, squamous epithelial cells, bacteria, fungi |
| Flags contamination | No | No | Yes |
| Reflex to culture | No | No | Often |
| Pathogen identification | No | No | No |
| Antibiotic susceptibility results | No | No | No |
What is urine culture?
Urine culture is a laboratory diagnostic testing method used to identify pathogens present in a urine sample. As opposed to urinalysis, whose purpose is to screen urine for indicators of infection and inflammation, a urine culture identifies which organism is growing in your urine and how much of it there is. For a first-time, uncomplicated UTI, many providers treat based on symptoms and a urinalysis alone. A culture is more likely when infections keep coming back, symptoms don’t improve with treatment, or someone is pregnant, uses a catheter, or has another condition that makes a UTI more complicated. For people with recurrent UTIs, the American Urological Association recommends a urinalysis and a urine culture with antibiotic susceptibility testing before treating each episode5.
Urine culture works by spreading a small volume of a urine sample across a petri dish containing growth media (nutrients) that facilitate the growth of common bacteria. The petri dish is incubated, usually for one to two days, so any bacteria present can grow into visible colonies. Results from a sample sent by a doctor’s office usually come back in two to five days. If anything grows, it is then identified through visual inspection or additional laboratory tests and quantified using a metric called colony-forming units per milliliter (CFU/mL).
What does urine culture detect?
Similar to urinalysis, there are different types of urine culture. The type of urine culture used is the major determining factor for what it can detect. When urine culture is discussed, it is most often referring to standard urine culture (SUC). This is the most common form of urine culture used by laboratories across the United States to diagnose UTI. SUC uses two types of growth media to try to grow bacteria or fungi from urine. It is strictly performed in aerobic conditions, or in the presence of oxygen2.
Certain laboratories may use a type of culturing method called enhanced quantitative urine culture (EQUC). EQUC uses a larger volume of urine, additional types of growth media, and a broader range of laboratory conditions as compared to SUC. This expanded range is more suitable for pathogens that are unable to grow under standard culture conditions. EQUC can also detect much lower counts of bacteria2.
Table 3: Standard urine culture vs. enhanced quantitative urine culture2
| Feature | Standard urine culture | Enhanced quantitative urine culture |
|---|---|---|
| Availability | Widely available, used by most diagnostic laboratories | Less available, performed by fewer diagnostic laboratories |
| Urine sample volume | 1 μL (microliter) | Up to three volumes: 1 μL, 10 μL, and 100 μL. The streamlined protocol uses 100 μL. |
| Growth media and conditions | 2 types of growth media, aerobic (in the presence of oxygen) | Up to 7 combinations of growth media and atmosphere (aerobic, anaerobic, 5% CO2, and microaerophilic). The streamlined protocol uses 3 types of growth media in 5% CO2. |
| Incubation time | 1-2 days | 2+ days (48 hours in the streamlined protocol) |
| Time to results | 2-5 days | 3-5+ days |
| Lowest count detected | About 1,000 CFU/mL | As low as 10 CFU/mL |
| Typical positive cutoff | ≥100,000 CFU/mL at many laboratories | Varies, no single standard |
| Detects | Most common aerobic bacteria | Aerobic and anaerobic bacteria, fungi, certain atypical pathogens |
| Misses | Anaerobic bacteria, most fungi, and atypical, fastidious, or intracellular pathogens | Fastidious pathogens, intracellular pathogens, and some atypical pathogens |
| Antibiotic susceptibility testing | No, requires antibiotic susceptibility testing following growth | No, requires antibiotic susceptibility testing following growth |
For people who do not have underlying medical conditions or a history of recurrent UTIs, urinalysis and standard urine culture are typically sufficient to get an accurate diagnosis. If you have medical conditions that increase your risk of complications from a UTI, or you have been struggling with recurrent UTIs, your provider may consider an advanced diagnostic like EQUC. However, it is important to know that like all diagnostic tests, EQUC has limitations. Despite outperforming standard urine culture2, EQUC may still struggle to identify fastidious, intracellular, and certain atypical pathogens that are known to cause UTIs. Antibiotic susceptibility testing can further delay pathogen-matched treatment, as it has to be performed on the bacteria isolated from the culture. Because of these limitations, providers are increasingly turning to DNA-based diagnostic tests, especially when culture returns negative despite urinalysis results suggesting infection.
How to give a reliable urine sample
How a sample is collected and handled affects the results of both tests. A few steps help make results more reliable:
- Use the clean-catch method: Wash your hands, clean the genital area with the wipe provided, and start urinating into the toilet before collecting the middle part of the stream in the cup. This lowers the chance of picking up microbes from the skin and genital area.
- Collect before starting antibiotics when possible: Antibiotics can stop bacteria from growing in culture, even when an infection is still present.
- Let urine sit in the bladder first: Nitrite takes time to form, so urine that has been in the bladder longer, such as first-morning urine, gives a more reliable nitrite result.
- Get the sample to the laboratory quickly: Urine should be tested within about two hours of collection, or refrigerated or stored in a preservative tube if there will be a delay4.
- Tell your provider if you’re menstruating: Blood from menstruation can affect urinalysis results.
How do you interpret urinalysis and culture results?
Urinalysis and urine culture results should always be interpreted in context by a healthcare provider. Here is a summary of common result combinations and what they may mean for you.
Table 4: Interpretation of common urinalysis and urine culture results
| Urinalysis | Urine culture | Interpretation | Questions to ask |
|---|---|---|---|
| Signs of infection (white blood cells, leukocyte esterase, and/or nitrites) | One uropathogen | If symptomatic, confirmed UTI. | Which pathogen grew? Is it susceptible to the antibiotic I was prescribed? |
| Signs of infection (white blood cells, leukocyte esterase, and/or nitrites) | “No significant growth”, or growth below the laboratory’s reporting cutoff | Many labs use 100,000 CFU/mL as the cutoff for a positive result, though lower counts may still indicate infection for certain pathogens or in certain patients | What count was actually found? Was the organism identified? Should a lower threshold be considered for my case? |
| Signs of infection (white blood cells, leukocyte esterase, and/or nitrites) | No growth | Potential culture-negative UTI. Advanced testing and other conditions that cause inflammation, such as kidney stones, may be considered. | Had I taken any antibiotics before this sample? Would advanced testing help? Should we test for anything else? |
| No signs of infection | Growth | If symptoms are present, urinalysis may have missed the infection. If no symptoms present, it may be asymptomatic bacteriuria or colonization. | Does this count and organism matter given my symptoms? |
| No signs of infection | No growth | Potential culture-negative UTI. Advanced testing and other conditions that can mimic UTI may be considered | What else could cause these symptoms? Would repeat or advanced testing help? |
| Any result | “Mixed growth” or “potential contamination” | Potential polymicrobial UTI, or microbes from the skin or vagina found their way into the sample | Should I give a new sample? Could a different collection method help? Would advanced testing help? |
What is NGS urine testing?
Next-generation sequencing (NGS) reads the DNA in a urine sample and matches it against a database of known organisms. Because it doesn’t rely on growing organisms in a lab, it can detect microbes that culture misses. Clinical metagenomics, the approach Biotia uses, sequences DNA from every organism in the sample instead of one targeted gene. That lets the test look for antibiotic resistance genes as well as pathogens. To see how NGS compares with PCR and culture, read more about how UTIs are diagnosed.
Our test, the BIOTIA-ID Urine Test, detects 44 key urogenital pathogens and 21 antibiotic resistance genes, and is available for at-home collection. Through our test-to-treat service, patients can get connected to a UTI specialist telehealth provider from Clinova Solutions to discuss their symptoms, test results, and treatment options without an in-person visit.
Frequently asked questions
What’s the difference between urinalysis and urine culture?
A urinalysis checks urine for signs of infection, such as white blood cells and nitrites. It can be done with a test strip in minutes or in a laboratory. A urine culture grows bacteria or fungi from urine so a laboratory can identify them and, with follow-up susceptibility testing, see which antibiotics work. A urinalysis suggests whether an infection is likely. A culture shows what is causing it.
What is urinalysis?
A urinalysis checks urine for signs of infection, inflammation, and other health problems. For UTIs, it looks for markers like white blood cells and nitrites. It can be a quick test strip at home or in a clinic, or a more complete exam in a laboratory. It doesn’t identify which organism is causing an infection.
Are urine dipsticks accurate?
Urine dipsticks are reasonably good at ruling out a UTI when leukocyte esterase and nitrites are both negative, but they are weak at confirming one. A positive result usually needs confirmation [1]. A laboratory urinalysis reads the strip with an instrument and can add a microscopic exam, but it still can’t identify what is causing an infection.
Is an at-home UTI test strip the same as a urinalysis?
Not quite. Most at-home UTI test strips check only for leukocyte esterase and nitrites, two of the markers in a full urinalysis. A laboratory urinalysis checks more chemical markers and adds a microscopic exam. A home strip can be a useful first check, but it can’t identify what is causing an infection, and a negative result doesn’t always rule one out.
Can you have a UTI without nitrites?
Yes, you can have a UTI without nitrites. Only certain UTI-causing bacteria will produce nitrites. Your UTI may be caused by bacteria or fungi that do not produce nitrites, such as Enterococcus or Candida species.
What is a urinalysis with reflex to culture?
Urinalysis with reflex to culture is a type of laboratory order made by a provider. This informs the laboratory that if the results from the urinalysis suggest that an infection is likely, then the urine should be cultured to identify what pathogens may be present.
What is urine culture?
Urine culture is a type of laboratory diagnostic test that attempts to grow pathogens from a urine sample. It can be further broken down into standard urine culture (SUC) and enhanced quantitative urine culture (EQUC), which differ in the number of growth media and conditions used, detection thresholds, time to results, and pathogen coverage. Most diagnostic laboratories use SUC, whereas EQUC is typically offered in more specialized laboratories.
How long does a urine culture take?
Most urine cultures are incubated for one to two days. When a sample is sent from a doctor’s office to an outside laboratory, results usually come back in two to five days. Identifying the organism and running antibiotic susceptibility testing can add time, as can slow-growing organisms.
What does 100,000 CFU/mL mean?
Urine culture quantifies bacteria present in urine based on the number of colony-forming units (CFU) per milliliter (mL) of urine. The typical positivity threshold for standard urine culture is ≥100,000 CFU/mL. However, infections can occur at much lower counts. In a study of women with UTI symptoms, the 100,000 CFU/mL cutoff identified only about half of those with coliform bacteria in their bladder, while a cutoff of 100 CFU/mL performed best [3]. Lower amounts of bacteria in urine may be considered a positive result depending on the species present or whether the patient has certain medical conditions.
Does finding bacteria in urine always mean a UTI?
No. Bacteria can be present in urine without causing an infection. This is called asymptomatic bacteriuria, and it is common in many groups, including older adults and people with urinary catheters. Guidelines generally recommend against treating it, with exceptions that include pregnancy and before certain urologic procedures [6].
What does “mixed flora” urine culture results mean?
“Mixed flora” urine culture results mean that multiple species grew in a urine culture. Species that grow in cultures reported as “mixed flora” are usually not identified or tested for antibiotic susceptibility by the laboratory. “Mixed flora” results can occur for a variety of reasons. The most common explanation is that the sample picked up microbes from the skin or genital area during collection. Another explanation is that the person has a polymicrobial UTI, or a UTI caused by more than one pathogen. Ask your doctor if repeat or advanced diagnostic testing may be appropriate.
Can urine culture miss bacteria?
Yes, urine culture can miss bacteria. Most laboratories use standard urine culture which attempts to grow bacteria from urine using a narrow set of conditions. It is particularly poor at growing anaerobic, atypical, fastidious, intracellular, and slow-growing bacteria. In a study of adult urogynecology patients, standard urine culture missed 67% of the uropathogens found by an expanded culture method, and half of those in patients with severe urinary symptoms [2].
References
- Devillé WLJM, Yzermans JC, van Duijn NP, Bezemer PD, van der Windt DAWM, Bouter LM. The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy. BMC Urol. 2004;4:4. doi:10.1186/1471-2490-4-4. PMID: 15175113. ↩
- Price TK, Dune T, Hilt EE, et al. The clinical urine culture: enhanced techniques improve detection of clinically relevant microorganisms. J Clin Microbiol. 2016;54(5):1216-1222. doi:10.1128/JCM.00044-16. PMID: 26962083. ↩
- Stamm WE, Counts GW, Running KR, Fihn S, Turck M, Holmes KK. Diagnosis of coliform infection in acutely dysuric women. N Engl J Med. 1982;307(8):463-468. doi:10.1056/NEJM198208193070802. PMID: 7099208. ↩
- Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician. 2005;71(6):1153-1162. PMID: 15791892. https://pubmed.ncbi.nlm.nih.gov/15791892/ ↩
- Anger J, Lee U, Ackerman AL, et al. Recurrent uncomplicated urinary tract infections in women: AUA/CUA/SUFU guideline. J Urol. 2019;202(2):282-289. doi:10.1097/JU.0000000000000296. PMID: 31042112. ↩
- Nicolle LE, Gupta K, Bradley SF, et al. Clinical practice guideline for the management of asymptomatic bacteriuria: 2019 update by the Infectious Diseases Society of America. Clin Infect Dis. 2019;68(10):e83-e110. doi:10.1093/cid/ciy1121. PMID: 30895288. ↩