Urine Leukocytes

The test shows whether white blood cells are present in urine. This is done in two ways, and they do not measure the same thing.

The dipstick carries a pad for leukocyte esterase, an enzyme from the granules of neutrophil granulocytes, the white cell most abundant in an acute inflammatory response. The pad changes colour once that enzyme is present. It does not see the cell; it sees what the cell leaves behind. That explains a result which often causes confusion: the strip can read positive while the laboratory finds few or no intact cells under the microscope. The cells have already broken down, for example in very dilute urine or in a sample left standing too long. This is not a measurement error. It is exactly what an enzyme pad is for.

Microscopic urine sediment counts the cells directly, per high-power field. That count is more specific and is done in the laboratory, not on a home dipstick.

The dipstick result is semi-quantitative and carries no unit:

The scale rises with the amount of enzyme, not with the severity of any condition. A 3+ on a cleanly collected sample deserves a doctor's interpretation, but is not by itself a diagnosis.

The leukocyte pad is a sensitive but poorly specific test, and those two properties together determine what a result is worth.

Sensitive means it rarely misses genuine inflammation: reported sensitivity sits broadly between 70 and 90 percent. Poorly specific means a positive also arises without infection. Specificity is clearly lower than sensitivity, which is why a positive leukocyte pad on its own is weak evidence. It mainly rules out; it establishes little.

The result gains considerable value alongside nitrite. Nitrite appears when certain gut bacteria convert nitrate in urine, and it behaves in exactly the opposite way: insensitive, but highly specific. Leukocytes positive and nitrite positive in someone with pain on passing urine and urgency makes a bacterial urinary tract infection likely. Leukocytes positive with nitrite negative leaves the question open, partly because not every organism converts nitrate.

Clinically the most interesting pattern is detectable leukocytes with a negative culture: sterile pyuria. That calls for a different line of thought rather than another urine test. Explanations include a recently treated urinary tract infection, a sexually transmitted urethritis such as chlamydia, interstitial cystitis, kidney stones, interstitial nephritis often triggered by medication, and more rarely tuberculosis. In a young adult with pain on passing urine and a negative culture, testing for a sexually transmitted infection is a more logical next step than repeating the urine culture.

The result establishes no diagnosis and is never on its own a reason for antibiotics. That judgement belongs to a doctor, weighing the result together with your symptoms and history.

The test belongs with symptoms pointing at the urinary tract: pain or burning on passing urine, needing to go more often, urgency without result, cloudy or strong-smelling urine, or lower abdominal pain. It is also requested as part of a broader urine screen, for example when checking kidney function or assessing unexplained fever.

Collection technique determines reliability more than the strip does. Collect a midstream sample: let the first flow pass, collect after that, and stop before the bladder is empty. Clean the area first. A morning sample is the most concentrated and therefore the most informative, though note the limitation under the results below. Deliver the sample to the laboratory within two hours or keep it refrigerated; in urine left standing, cells break down and bacteria continue to grow.

Avoid testing during menstruation. Blood and discharge will almost always enter the sample and make the result unusable.

With fever, chills, flank pain or nausea, contact a doctor the same day. That picture may fit a kidney infection and does not wait for a dipstick.