Leukocytes in Urinalysis: The Significance Of White Blood Cells In A Urine Sample

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Normal Urine

This article is a companion piece to an article on the meaning of white blood cell counts in blood analysis. The focus of this article is to explain the significance of leukocytes in a patient’s urine sample.

White blood cells, or leukocytes, are involved in the body’s immune response to illnesses or injuries. Under normal circumstances, a healthy person’s urine will not contain any blood cells since these will be removed by the kidneys and ultimately excreted as a component of faeces. Except in cases of injury or disease, there is no contact between the blood system and the urinary system. Consequently, the presence of leukocytes in urinalysis is indicative of a health problem. The presence of red blood cells in the urine is referred to as hematuria and, in the absence of a recent injury which could explain it, should always be referred to a clinician as it can be a symptom of a potentially serious illness (although the condition may also be perfectly harmless).

The Significance Of Leukocytes In Urine

The normal cause of the detection of leukocytes in urinalysis is an underlying infection within the urinary tract. A urinary tract infection is usually caused when bacteria enter the urethra; the urethra is the part of the body from which urine is expelled from the body. This type of infection is referred to as urethritis. The infection may then become established in the bladder (a condition also known as cystitis) or can spread back to the kidneys (such an infection is usually referred to as pyelonephritis by clinicians). The ureters are the tubes which connect the kidneys to the bladder and they may also become infected, but this is a fairly rare condition.

Women are at greater risk for a urinary tract infection than men because of their physiology; their urethras are shorter and are in closer proximity to the anus. Women are also at a greater risk of picking up a urinary tract infection during sexual intercourse than men.

Urinary Tract Infection - Frequency And Treatment

A urinary tract infection will usually be detected by urinalysis of a small sample of urine. The urine will be tested for the presence of leukocytes, proteins, red blood cells and possibly nitrites. The test can usually be performed in the doctor’s surgery by the doctor or a nurse and interpreted immediately.

A urinary tract infection is usually treated by a course of antibiotic medicine (which should always be followed for the full prescribed duration and not broken off once the symptoms have abated). It may be necessary to culture the bacterial infection (from the urine sample) such that the bacterium can be identified to ensure that an appropriate antibiotic is prescribed (but this tends to be restricted to patients who are known to be unresponsive to the usual broad spectrum antibiotics).

Estimates suggest that between 8 to10 million people will suffer from a urinary tract infection each year in the USA. One in five women will experience this type of infection and within this group, roughly 20% will suffer from recurrent urinary tract infections.


  1. Hematuria, National Institutes of Health: https://kidney.niddk.nih.gov/kudiseases/pubs/hematuria/
  2. Urinary Tract Infection, Medline Plus, NIH: https://www.nlm.nih.gov/medlineplus/ency/article/000521.htm
  3. Urinary Tract Infection: https://www.urologychannel.com/uti/index.shtml