The presence of a high number of leukocytes or white blood cells (WBCs) in a urine test may be a sign of infection or inflammation of the urinary tract.
Normally, there should not be more than a few leukocytes in the urine (4–5 per high-power field) when studying under the microscope the urine sediment. However, higher numbers may be present in urine from females.
Leukocytes or WBCs may come from anywhere in the genitourinary tract.
The presence of a high number of leukocytes in the urine sediment may help to diagnose infection or inflammation of the urinary tract.
There are two groups of leukocytes or WBCs: polymorphonuclear (neutrophils, eosinophils and basophils) and mononuclear (lymphocytes and monocytes).
Most of those present in the urine sample are neutrophils, although eosinophils or mononuclear cells may be elevated in certain situations.
Eosinophils are not normally seen in the urine. The presence of eosinophils is primarily associated with urinary tract infection (UTI). There are other possibilities for a high presence of eosinophils in urine such as a drug-induced interstitial nephritis or a renal transplant rejection. Lymphocytes may be also seen in increased numbers in the early stages of renal transplant rejection.
This test is performed along with other urine tests. The patient must collect a sample of the urine in a specific container using a special kit. This sample will be sent to the lab for the analysis. The urine should be collected by a clean-catch midstream to rule out bacterial contamination.
It is important to avoid vaginal discharge because it can contaminate the sample.
To study the presence of WBCs in the urine, it is necessary to obtain previously the urinary sediment. For this matter, the urine sample should be placed at rest for some hours waiting for the different elements of the urine (white and red blood cells, crystals, etc.) precipitate to the bottom. As this process is very slow, the urine is centrifuged for about 5 minutes at 1500 or 2000 revolutions per second to obtain a sample of the sediment in less time.
It is considered normal to see fewer than five leukocytes per HPF (High Power Field), when examining under the microscope the urine sediment with a high-power magnification.
The presence of more than 5 leukocytes per HPF (High Power Field) is considered important for diagnosis. The number of WBCs cells identified using the high-power objective is reported.
Elevated numbers of white blood cells in the urine is called pyuria, which indicates infection (mainly bacterial) or inflammation of the urinary tract. Pyuria is defined as the presence of 10 or more WBCs per cubic millimeter in a urine sample.
Some conditions that may be related to pyuria or a high number of WBCs in a urine test are:
It is common to see bacteria in urine when pyuria is present.