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Written by: Barbara Hebert, MLS
A UTI test strip and dipstick test for leukocytes and nitrites in the urine. When your urine is nitrite positive, it likely means there’s a bacterial infection. Leukocyte negative means that the amount of white blood cells in your urine are low and not secreting leukocyte esterase, which is a compound white blood cells excrete when they’re activated, or fighting off an infection.
Urinary tract infection test strips are a quick, easy, and cost effective way to test for a UTI at home. The test works by testing for nitrites and leukocytes in the urine. When both nitrites and leukocytes come up as positive, it is very likely a UTI is present.
However, for many of us, we’ve had the experience of being uncertain about our test strip findings — do I really have a UTI? Here, we explore what exactly are leukocytes and nitrites, and how they are used to diagnose a possible UTI.
What are leukocytes?
Leukocytes are also known as white blood cells, which are an important part of your immune system. Types of leukocytes include: granulocytes (which are made up of neutrophils, eosinophils, and basophils), monocytes, and lymphocytes (T cells and B cells). Together, all of these white blood cells help the body fight infection, inflammation, and other illnesses or diseases.
What does it mean if you have leukocytes (or white blood cells) present in a urine test?
When your body is fighting off an infection, your immune system will send white blood cells to combat any foreign invaders (think: bad bacteria). This is where checking the number of leukocytes (and their components) is a useful tool to help identify the presence of various conditions including infection or inflammation.
If your body’s white blood cells are increased, and are out of a ‘normal’ reference range* then, you guessed it, your body is likely fighting off some type of illness.
A leukocyte esterase (LE) test is just one such test, and is a compound that can be easily checked for on your urine dipsticks to screen for UTI, and can catch an asymptomatic (or early stage) infection. An LE test can also come back positive for infections such as Trichomonas and Chlamydia.
*Normal reference ranges can vary by lab. As always, consult with your doctor to see what reference ranges were used for your test and be sure to voice any concerns you may have.
So how does an LE test catch a UTI (or other infection) before you even notice it? This is because granulocytic cells all have esterases in them. Neutrophils (one of the types of granulocytes) are the first “cops on the scene” in an immune response, and their presence will be detected by an LE test even before you start to experience noticeable symptoms.
However, it’s important to note that white blood cells can be present in the bladder for other reasons (such as inflammatory disorders), and sometimes even after antibiotic therapy, so a positive LE test does not necessarily mean there are bacteria present (1).
On the other hand, when an individual has a suppressed or compromised immune system, leukocyte production is naturally low. This results in a low or negative LE test in patients despite presence of an infection. For these individuals, different testing methods may be warranted (such as a blood test) (2).
False-positive LE test
On occasion, a false-positive LE test result is possible. A false-positive result can be caused by various factors including:
- oxidizing agents (such as bleach used in the manufacturing of dipsticks)
- when the urine is colored (which could be caused by drugs like Nitrofurantoin/Macrobid, supplements, and/or diet)
- bilirubin (liver disease)
- gross hematuria (or blood)
- AZO products (from my observations, AZO products color the supposing and can interfere with any test because of the color change)
A “dirty catch” urine sample may also contaminate a specimen with leukocytes from the vagina, which is why you may be asked to clean yourself and catch urine midstream; however, the current scientific evidence suggests that cleansing procedures may not be necessary as they have not been shown to decrease urine contamination significantly. (3, 4)
False-negative LE test
Conversely, a false-negative result may also occur on occasion. A false-negative result could be influenced by (5):
- antibiotic use
- elevated sugar levels in the urine
- vitamin C (ascorbic acid) in large amounts
- menstrual blood
- concentrated urine
- strenuous exercise
- old infections (because the type of leukocyte that appears later in the infection is lymphocytes, which do not contain LE)
What are nitrites?
First, it’s important to know that nitrates are compounds normally found in urine, and may have a higher presence in some individuals depending on dietary patterns (some vegetables, like spinach, are naturally rich in nitrates). And if you’re still wondering what nitrate is - try to think back to that science class where you learned about the Nitrogen Cycle. The Nitrogen Cycle is important for all living organisms, and is something humans contribute to by eating foods rich in nitrate (a compound of 1 nitrogen and 3 oxygen molecules). That’s the really simplistic version, but hopefully helps to set the stage for the rest of this section.
When specific bacteria enter the urinary tract (such as E. coli, a common bacteria found in your gut), those dietary nitrates will be converted into nitrite (a compound of 1 nitrogen and 2 oxygen molecules). Because these specific bacteria can reduce nitrate to nitrite, infections with these organisms may show a positive nitrite result on the dipstick.
The usefulness of the nitrite test is limited, however, as nitrite production is not associated with other urinary tract pathogens such as Pseudomonas or even enterococci. (6)
A test for nitrites can also come back negative if the urine is excreted before the reduction of nitrate to nitrite can take place. Some references estimate this reaction can take up to 4 or 6 hours! (7,8) As we all know, it’s very difficult to hold urine when we have a UTI.
False-negative nitrite result
Just like with the LE test, false-negative nitrite results can occur and can be influenced by the following:
- when there is a low amount of nitrate in the urine due to low dietary nitrate intake
- high concentrations of vitamin C
- if the conversion of nitrite to nitrogen has occurred (for example, in specimens that have not been tested for several hours)
- urine having an acidic pH (<6.0)
False-positive nitrite result
False positives can occur when:
- dipsticks have been stored improperly or exposed to air
- conversion of nitrate to nitrite due to bacterial contamination in an improperly collected or stored urine specimen
- AZO use (your urine should be tested before any AZO use)
- gross blood (from my observation, because of the color, it can give a false positive on any test)
Bottom line is a negative nitrite value does not necessarily mean there is no infection present. It may only indicate the type of bacteria that are, or are not, present, assuming proper storage and handling conditions were met. So, as with everything, check with your doctor about what standard reference ranges are being used to determine any abnormal presence.
Negative leukocytes and positive nitrite result?
Sometimes results can show a negative LE and a positive nitrite. As already discussed, this could be caused by improper storage of the dipsticks or urine or could happen if the patient is immunocompromised. One thing that can be done to show a more precise dipstick result is to make sure the dipsticks are stored properly, and ensure the doctor knows if you have been diagnosed with an immune-compromising disorder and/or an illness requiring immune-suppressing therapies (such as lupus).
Again, if you have any questions regarding your test results, please talk with your doctor ASAP, especially if your symptoms are unresolved or worsening. It’s okay to ask to have a sample of clean-catch urine to undergo microscopic evaluation of urine sediment or ask if other tests should be performed. From there, your doctor can decide whether a culture and/or antibiotic sensitivity test are needed based on the specimen results and symptoms.
And one more note: I work in a rural hospital/clinic, so we lab techs talk with the provider about what we see in the microscope. Sometimes we will advise them if a specimen is properly sampled and tested to perform a culture. Communication is most important!
1. Martina Franz, Walter H. Hörl, Common errors in diagnosis and management of urinary tract infection. I: Pathophysiology and diagnostic techniques, Nephrology Dialysis Transplantation, Volume 14, Issue 11, November 1999, Pages 2746–2753, https://doi.org/10.1093/ndt/14.11.2746
2. Ramakrishnan K & Scheid DC. Diagnosis and management of acute pyelonephritis in adults. Am Fam Physician. 2005 Mar 1;71(5):933-942.
3. Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician. 2005 Mar 15;71(6):1153-1162.
4. Michael L. Wilson, Loretta Gaido, Laboratory Diagnosis of Urinary Tract Infections in Adult Patients, Clinical Infectious Diseases, Volume 38, Issue 8, 15 April 2004, Pages 1150–1158, https://doi.org/10.1086/383029
5. Bacârea A, Fekete GL, Grigorescu BL, Bacârea VC. Discrepancy in results between dipstick urinalysis and urine sediment microscopy. Exp Ther Med. 2021;21(5):538. doi:10.3892/etm.2021.9971
6. Wilson ML & Gaido L. Laboratory diagnosis of urinary tract infections in adult patients. Clin Infect Dis. 2004;38(8):1150-1158. https://doi.org/10.1086/383029
7. Tiso M, Schechter AN. Nitrate reduction to nitrite, nitric oxide and ammonia by gut bacteria under physiological conditions [published correction appears in PLoS One. 2015;10(5):e0127490]. PLoS One. 2015;10(3):e0119712. Published 2015 Mar 24. doi:10.1371/journal.pone.0119712
8. Wilson ML & Gaido L. Laboratory diagnosis of urinary tract infections in adult patients. Clin Infect Dis. 2004;38(8):1150-1158. https://doi.org/10.1086/383029
9. Urinalysis and Body Fluids: A Colortext and Atlas, Karen Munson Ringsrud and Jean Jorgenson Linne, Copyright 1995.
10. Emergency Medical News, Urine Dipstick Testing has Limitations, but is Still Useful in the ED, James R. Roberts, MD, 11/17/2020.
About the author
Barbara Hebert, MLS( ASCP) CM, is a Medical Laboratory Scientist in rural Montana. She also happens to be a Uqora customer! She has been a laboratory professional since 2012. She has amassed many hours in the laboratory analysis of urine, including dipstick, microscopic examination, and culturing of specimens. She has also performed antibiotic sensitivities of the organisms causing infection.
What would the presence of nitrites and/or leukocytes in urine indicate? ›
So, if you have nitrites in your urine, it usually means that you have a urinary tract infection (UTI). UTIs are one of the most common types of infections, especially in women. Most UTIs affect the bladder and urethra (the tube that carries urine out of your body). Fortunately, most UTIs are not serious.What are leukocytes in UTI? ›
Leukocyte esterase is a screening test used to detect a substance that suggests there are white blood cells in the urine. This may mean you have a urinary tract infection. If this test is positive, the urine should be examined under a microscope for white blood cells and other signs that point to an infection.What does it mean if you have positive leukocytes and negative nitrates? ›
Leukocytes in the urine without nitrite
If the test for leukocyte esterase is positive but finds no nitrite, an infection may still be present. The test is particular to certain bacterial enzymes, which means it can pick up specific bacterial infections with more certainty.
What is nitrite-positive urine? Nitrite-positive urine (pee) is a sign of a possible urinary tract infection (UTI). Healthy urine contains nitrates, a type of nitrogen chemical. When bacteria enter your urinary tract, the bacteria turn these nitrates into a different nitrogen chemical called nitrites.Which is more indicative of UTI leukocytes or nitrites? ›
Therefore, the clinical impression that leukocyte esterase is the more sensitive test (more likely to be the sole indicator of UTI) and that the presence of nitrite is highly specific (i.e., highly predictive of UTI) appears to still hold.When urine is positive for leukocytes and nitrates? ›
A urine sample that tests positive for both nitrate and leukocyte esterase should be cultured for pathogenic bacteria. These tests are indirect ways of detecting bacteria in the urine. Significant urinary tract infections may be present in patients who do not experience other symptoms.What is the difference between leukocyte and nitrite in UTI? ›
When your urine is nitrite positive, it likely means there's a bacterial infection. Leukocyte negative means that the amount of white blood cells in your urine are low and not secreting leukocyte esterase, which is a compound white blood cells excrete when they're activated, or fighting off an infection.What does it mean if a UTI test is positive for leukocytes? ›
Leukocyte esterase is a screening test used to detect a substance that suggests there are white blood cells in the urine. This may mean you have a urinary tract infection . If this test is positive, the urine should be examined under a microscope for white blood cells and other signs that point to an infection.What level of leukocytes indicate UTI? ›
You're bound to have a few WBCs in your urine even when you're healthy, but if a urine test identifies levels above 5 wbc/hpf, it's likely you have an infection. If bacteria are detected, your doctor may perform a urine culture to diagnose the type of bacterial infection you have.Can you have leukocytes in urine but no bacteria? ›
It is possible to have white blood cells in the urine without a bacterial infection. Sterile pyuria refers to the persistent presence of white blood cells in the urine when no bacteria are found to be present by laboratory examination.
What is the most common cause of leukocytes in urine? ›
Urinary Tract Infection (UTI)
An infection in your urinary tract is the most likely cause of leukocytes in your urine. Any time you have an infection, your immune system ramps up production of these cells to fight off the bacteria.
In some cases, the levels of leukocytes in your urine may increase in the absence of a bacterial infection. This condition is known as sterile pyuria. Sexually transmitted infections (STIs), fungal infections, and parasitic infections can all cause sterile pyuria.Does nitrite in urine mean yeast infection? ›
The presence of nitrites in urine most commonly means there's a bacterial infection in your urinary tract. This is usually called a urinary tract infection (UTI). A UTI can happen anywhere in your urinary tract, including your bladder, ureters, kidneys, and urethra.Can stress cause leukocytes in urine? ›
We concluded from the above study that percentage of normal individuals having leukocytes in their urine is greater than happy individuals. So, there is a connection between normal individuals and anxiety level.What bacteria causes nitrates in urine? ›
E. coli bacteria are most commonly associated with nitrites in the urine. Having leukocytes in the urine without nitrites can also lead to a false-positive result that points to a bacterial infection when there is none.What does it mean if you have high leukocytes? ›
Leukocytosis means you have a high white blood cell count. This means you have more white blood cells than normal. Leukocytosis is a normal immune response and isn't always a cause for concern. Most of the time, it means that your body is fighting off infection or inflammation.What antibiotic treats leukocytes in urine? ›
Ciprofloxacin (Cipro) or levofloxacin (Levaquin)
These types of antibiotics work slightly better than amoxicillin/potassium clavulanate, cefdinir, and cephalexin. But the risk of serious side effects is higher. Healthcare providers usually save these antibiotics for more complicated or severe types of UTIs.
A Doctor is likely to recommend a course of antibiotics to treat the infection that caused the leukocytes to be there in the first place. Once the antibiotics take effect the concentration of white blood cells in urine will decrease to a normal level.Does leukocytes in urine mean kidney infection? ›
If leukocytes in urine are found this can be an indication of Urinary Tract Infection (UTI). To be certain it is recommended at this stage to visit your Doctor to confirm a diagnosis and receive treatment. An untreated UTI can be very painful and with very advanced infections cause permanent damage to the Kidney.How do I read my UTI test results? ›
A few white blood cells are normally present in urine and generally yield negative results. When the number of WBCs in urine increases significantly, the urine dipstick screening test will become positive. Presence of leukocytes (>10 leu/µL) in urine may indicate infections in the urinary tract or kidneys.
How do you read a UTI lab results? ›
On the Clarify package, there is a color-coded range to help you decipher your test strip results. The top panel is testing for leukocytes and the bottom panel is testing for nitrites. If both pads are purple in color, this is a clear indicator that a UTI is most likely present.What levels indicate a UTI? ›
Any amount of bacteria in the urine may suggest UTI in a symptomatic patient, but the threshold for the classic definition of bacteriuria is 5+, which is roughly equivalent to 100,000 colony-forming units (CFUs)/mL.
Certain medications (antibiotics, aspirin, corticosteroids, diuretics) may cause the appearance of leukocytes in the urine (in this case, eosinophils).How can I get rid of leukocytes in my urine naturally? ›
Drink parsley water: It is a natural diuretic and can help flush out your system. Consume more blueberries: They contain ingredients that can work to prevent and treat UTIs. Consume diluted apple cider vinegar: It is a natural antibacterial, so it can help fight off bacteria in the urinary system.What can leukocytes in urine mean other than UTI? ›
High levels of leukocytes in your urine may indicate you have a condition such as a urinary tract infection (UTI), kidney stones, or pelvic tumor. Risk factors include pregnancy and a compromised immune system.What types of bacteria cause nitrites in urine? ›
E. coli bacteria are most commonly associated with nitrites in the urine. Having leukocytes in the urine without nitrites can also lead to a false-positive result that points to a bacterial infection when there is none.What is the difference between leukocytes and nitrite UTI? ›
When your urine is nitrite positive, it likely means there's a bacterial infection. Leukocyte negative means that the amount of white blood cells in your urine are low and not secreting leukocyte esterase, which is a compound white blood cells excrete when they're activated, or fighting off an infection.Does azo cause positive nitrite? ›
In addition, false-positive results for nitrite will occur if the dipstick is exposed to air or phenazopyridine, a common prescription and OTC product (e.g., Pyridium, AZO) used as a urinary analgesic.What antibiotic is used for nitrates in urine? ›
Nitrofurantoin is an oral antibiotic that is used in the treatment and prevention of lower UTIs.Do nitrites cause inflammation? ›
Recent animal and human studies have shown that dietary nitrate and nitrite also modulate inflammatory processes and immune cell function and phenotypes. Chronic low-grade inflammation and immune dysfunction play a critical role in cardiovascular disease.