Sterile pyuria is when a urine sample has more white blood cells than normal but no infectious organisms. It can be caused by contamination, tumors, or noninfectious diseases. Further testing may be needed to identify the underlying cause.
Sterile pyuria is a term used to describe the result of a specific urine sample test. It is used when a urine sample is negative for infectious organisms but there are more white blood cells than normal. There are several reasons a doctor may find pyuria sterile, and in some cases, an infectious organism may actually be present.
One of the reasons urine samples are taken is to diagnose infectious diseases of the urinary tract. Changes in white blood cell levels are an indication of the presence of an infectious disease. An infection can be identified by culturing the causative organisms from urine.
An official lab result of pyuria can have many potential causes. These range from sample contamination to the presence of tumors. Sterile pyuria is a relatively common laboratory finding. Women who appear to have urinary tract infections are the most likely group to have pyuria.
A patient who has been treated in the previous two weeks for an existing urinary tract infection may show elevated white blood cell levels but no organisms. Accidental contamination of the sample with an antiseptic can kill any microorganisms present. Sometimes, vaginal white blood cells can be accidentally mixed with urine during sampling, resulting in a higher than normal level of cells in the sample. Occasionally, urine may be highly diluted due to high fluid intake, which reduces the levels of infectious microorganisms in the specimen and reduces the likelihood of culture growth.
Some infectious organisms are not found through standard laboratory culture techniques. These include the sexually transmitted diseases chlamydia, gonorrhea or trichomoniasis. If a patient has tuberculosis affecting the genitourinary tract, the test will not identify it.
Noninfectious diseases that can show a high number of white blood cells in the urine include the inflammatory conditions prostatitis, nephritis, or sarcoidosis. Cancers of the kidney or bladder can also increase white blood cell levels. Kidney stones are another possible cause of sterile pyuria.
If a doctor suspects that sterile pyuria is caused by a disease that requires treatment, they may take more samples and order more tests. These tests include genital swab and specific culture for STDs or urine sampling and tests for tuberculosis. The lab may also check a urine sample for the presence of other blood cells that indicate the presence of diseases such as nephritis. The sample can also be checked for the presence of antibiotics.
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