Finding both nitrites and leukocytes on a urine test is a strong signal of a urinary tract infection. Nitrites indicate bacteria are present in your urine, while leukocytes (white blood cells) show your immune system is actively fighting something off. Together, these two markers have about 79% sensitivity and 81% specificity for detecting a UTI, meaning the combination is a reliable but not perfect indicator of infection.
A quick clarification: many people search for “nitrates” in urine, but what the dipstick actually measures is nitrites. The distinction matters, and we’ll explain why below.
What Nitrites in Urine Actually Mean
A normal urine test reads negative for nitrites. When nitrites show up, it means certain bacteria in your urinary tract are converting naturally occurring nitrates (which come from your diet, especially vegetables) into nitrites. This chemical conversion is something only specific types of bacteria can do, and those bacteria happen to be the most common causes of UTIs.
The bacteria most often responsible include E. coli (by far the most common, causing roughly 71% of uncomplicated UTIs), Proteus species, and Klebsiella. However, some bacteria that cause UTIs cannot convert nitrates to nitrites at all. Enterococcus, Pseudomonas, and Acinetobacter are notable examples. So a negative nitrite result does not rule out infection.
Several other factors can also produce a false negative on the nitrite test. If your urine hasn’t been sitting in your bladder long enough (less than four hours), bacteria may not have had time to produce detectable nitrites. A diet low in nitrate-containing vegetables reduces the raw material bacteria need. High vitamin C intake can also interfere with the test and mask a true positive.
What Leukocytes in Urine Mean
Leukocytes are white blood cells. When they appear in urine, it means your body is sending immune cells to fight inflammation or infection somewhere in the urinary tract. The dipstick doesn’t detect the cells directly. Instead, it picks up an enzyme called leukocyte esterase that white blood cells release. A normal result is negative.
While leukocytes most commonly point to a UTI, they can also show up without any bacterial infection present. This is called sterile pyuria, and it has a surprisingly long list of possible causes: kidney stones, interstitial cystitis (chronic bladder pain), lupus, poorly controlled diabetes, recent urological procedures, indwelling catheters, certain medications that irritate the kidneys, and even pregnancy. So leukocytes alone tell you something is going on, but not necessarily what.
Why the Combination Matters
Either marker alone is less convincing than both together. Leukocytes without nitrites could reflect inflammation from a non-infectious cause or an infection with bacteria that don’t produce nitrites. Nitrites without leukocytes are uncommon but can occasionally happen early in an infection before your immune response kicks in.
When both are positive, the picture becomes much clearer. You likely have bacteria in your urinary tract and your body is responding to them. This combination is what typically prompts a doctor to move forward with treatment or further testing rather than waiting.
What Happens After a Positive Result
The dipstick is a screening tool, not a definitive diagnosis. When both nitrites and leukocytes come back positive, the next step is usually to look at the urine under a microscope and, in many cases, send a urine culture. The culture identifies exactly which bacteria are present and which antibiotics will work against them. In one large study, doctors ordered a urine culture about 59% of the time after a positive urinalysis, compared to 32% of the time when the dipstick was negative.
Whether you actually need treatment depends heavily on symptoms. If you have burning with urination, urgency, frequency, pelvic pain, or cloudy and foul-smelling urine, treatment with antibiotics is standard. But if the positive result was found incidentally and you have no symptoms at all, guidelines from the Infectious Diseases Society of America and the CDC recommend against treating in most cases. Bacteria in the urine without symptoms (called asymptomatic bacteriuria) is common, especially in older adults, and treating it with antibiotics does more harm than good by promoting resistance without improving outcomes. The main exceptions are pregnant women and people about to undergo certain urological procedures, who do benefit from treatment even without symptoms.
What a Negative Result Tells You
When both markers are negative, you can feel fairly confident. The combination carries a negative predictive value of about 94.5%, meaning that when the dipstick reads negative for both nitrites and leukocytes, there’s roughly a 95% chance you truly don’t have a significant bacterial infection. That said, if you have clear UTI symptoms despite a negative dipstick, your doctor may still order a culture since the test isn’t perfect.
Common Scenarios and What They Suggest
- Nitrites positive, leukocytes positive: Strong indication of a bacterial UTI, especially one caused by E. coli or similar organisms. Further testing and treatment are typically appropriate if you have symptoms.
- Nitrites negative, leukocytes positive: Could be a UTI caused by bacteria that don’t produce nitrites, or a non-infectious cause like kidney stones, interstitial cystitis, or inflammation from another condition. A urine culture can help sort this out.
- Nitrites positive, leukocytes negative: Less common. May indicate early infection before your immune system has responded fully, or a sample issue. Usually warrants a closer look.
- Both negative: Reassuring. A UTI is unlikely, though not completely excluded if symptoms are present.
If you’re reading your own lab results and see positive values for both, the most likely explanation is a straightforward urinary tract infection. The practical next step is confirming with your healthcare provider whether a culture is needed and whether your symptoms warrant antibiotics.