Pyuria refers to the abnormal presence of a significant number of pus cells in urine. Pus is a yellowish fluid substance composed of protein-rich serum, dead white blood cells (also called leukocytes) that took part in inflammation and often bacterial cells. In response to an incendiary offending agent, like an infectious microbe, the body’s cellular immunity kicks in. Under the influence of cytokines, neutrophils (a kind of white blood cell) aggregate at the nidus of infection and attack and effectively kill the bacteria. Later, macrophage cells clear up the dead neutrophil debris which contributes to pus formation. Clinically, pyuria is defined as the presence of ten or more white blood cells per cubic millimetre of a urine sample.
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Pyuria caused by bacterial infection commonly tests positive on standard culture and sensitivity studies. Urinary tract infections (UTIs) are the most common cause; lower tract infections more than upper. There is also sterile pyuria, in which although a significant number of white blood cells is persistently detected in the urine sample microscopically, the urine tests negative on standard microbial culture studies. Sterile pyuria can be caused by both non-infectious and infectious diseases. Sterile pyuria is notably caused by genitourinary tuberculosis, kidney stones, tumours, sepsis, systemic lupus erythematosus (SLE), recent antibiotic therapy and even due to chronic use of certain drugs.
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Pyuria generally presents with a change in colour, odour, viscosity and opacity of the urine. Frequent urination, painful urination, an urgency to urinate or fever may be present. Other presentations vary depending on the underlying disease, as does their management. Bacterial urinary tract infections are treated with antibiotics after sensitivity testing. Drinking plenty of fluids is beneficial.
Additionally, while detection of pyuria is generally prompted by patient-reported signs and symptoms, asymptomatic pyuria can also occur.