White blood cells in urine

Finding White Blood Cells in urine

Increased number of White Blood Cells (WBCs) in urine signifies inflammation or infection. Medically, presence of WBCs in urine is called pyuria or pus in urine. White Blood Cells (also called leukocytes) are important part of your immune system. They are your inflammatory cells. They are your first responders to any kind of foreign invasion. White Blood Cells can squeeze out of your blood vessels and pass through tissue to reach organs with infection or irritation.

You can see White Blood Cells in urine by looking at the prepared slide of your urine sample under a microscope. You can count the number of White Blood Cells using the high power setting in the microscope. It may be normal to see up to 5 WBCs in a high power field of the microscope. More than 5 WBCs per high power field is considered abnormal.

Urinalysis usually involves dipstick and microscopic examinations. Dipstick exam is simply dipping a piece of strip to detect specific chemicals in your urine. Dipsticks cannot directly find leukocytes (WBCs) in urine but they can detect chemicals that provide indirect evidence of leukocytes. One of the chemicals they can detect is leukocyte esterase. It is a chemical released from breakdown of White Blood Cells in urine. When the dipstick is positive for leukocyte esterase, it is important to do a microscopic exam to look for actual White Blood Cells.

white blood cells in urine
white blood cells in urine

As you can see, your urinary tract includes two kidneys that connect to your single bladder with two ureters. The bladder connects to outside with your urethra. White Blood Cells in urine can originate in any of these places.

Now, we will explore the significance of White Blood Cells in urine in different settings.

White Blood Cells in urine with bacteria: definite infection

bacteria and WBCs in urine
bacteria and WBCs in urine

The presence or absence of significant number of WBCs in your urine is very important in making a diagnosis of urinary tract infection. Bacteria from your digestive tract or skin can climb up your urethra and settle down in your bladder. However, they are not always successful in causing infection. When you have a normal healthy urinary tract, you may be able to flush out these bacteria in your urine before they can cause any problems. When they examine your urine just after you flush them out, they may detect these bacteria.

Presence of bacteria in your urine is called bacteriuria and it may or may not suggest infection. Bacteria in urine can be from transient colonization without infection. If they leave your urine sample sitting down in the lab for some time, bacteria in the environment may contaminate the sample. This type of contamination may be another explanation of why bacteria were seen under the microscope.

Unlike bacteria, White Blood Cells cannot get in your urine by contamination. If they see bacteria as well as increased number of White Blood Cells in your urine, you can be fairly certain that you have actual urinary tract infection (UTI).

White Blood Cells in urine without bacteria: possible infection

Sometimes, they may find White Blood Cells in urine without bacteria. They may not see any bacterium in your urine when looking under the microscope but they may find significant number of White Blood Cells. This finding does not mean that you have no bacterial infection. The most common reason for White Blood Cells in urine with no bacteria is partially treated UTI. If you have taken antibiotics for UTI, it may have cleared your bacteria but the White Blood Cells may be present for some time.

However, there may be times when you have White Blood Cells in urine with possible infection from microorganisms that you cannot see in the microscope. Here is a list of some of the infections that can produce White Blood Cells in urine without being detected by the microscope:

  1. Tuberculosis and other mycobacterial infections: This category of bacteria needs special stain and specialized techniques to be detected in urine. They are not normally performed in routine urinalysis. People with these infections will only have WBCs seen in the usual microscopic examination.
  2. Viral infection (herpes, adenoviruses, varicella-zoster): Viruses are too small to be seen by a regular microscope but can cause white blood cells in urine.
  3. Yeast(fungi) infections: Yeasts may or may not be seen in the microscope but they usually grow in urine culture if present in the urine sample. Increased white blood cells along with detection of yeast in urine may signify fungal urinary tract infection.

White blood cells in urine: no infection

Irritation, trauma, cancer, blood vessel damage and other similar processes can cause White Blood Cells in urine.

Here is list of diseases affecting your whole body that may also result in White Blood Cells in urine with no infection:

  1. Diabetic nephropathy (kidney disease from uncontrolled diabetes)
  2. Sickle cell disease nephropathy (kidney disease as a result of complication of sickle cell anemia)
  3. Sarcoidosis (a disease of the immune system causing widespread inflammation in the body)
  4. Kawasaki disease (a rare disease that results in inflammation of blood vessels)
  5. Reactive Arthritis (a disease that results in inflammation of joints after certain infections)
  6. Systemic lupus erythematosis (commonly called “Lupus”- a disease of the immune system that may cause damage of multiple organ systems)

Here is a list of urinary tract and kidney specific diseases that may cause WBCs in urine with no infection:

  1. Polycystic kidney disease (an inherited disease that may lead to kidney failure)
  2. Backward flow of urine from bladder to kidneys called Vesicoureteral Reflux
  3. Kidney or ureter stones
  4. Retained foreign body
  5. Trauma from prostate surgery
  6. Any obstruction in normal flow of urine
  7. Accident or trauma involving urinary tract
  8. Extreme dehydration
  9. Interstitial nephritis (a type of swelling or inflammation of kidneys)
  10. When body rejects transplanted kidney
  11. Glomerulonephritis (inflammation and damage of urine making component of kidneys)
  12. Interstitial cystitis (Bladder inflammation of unknown cause)
  13. Tumor or cancer of any part of the urinary tract

White Blood Cells in urine as casts

Sometimes when you look at WBCs in urine under a microscope, you can see that they are not floating freely. They can be seen as groups of White Blood Cells joined together to form cylinder type shapes. These cylindrical shaped structures are called White Blood Cell casts. They are formed inside the kidneys. Our kidneys have small tubes where urine is formed. White Blood Cells originating in the kidneys get pressed into casts while coming down these tubes.

Finding WBCs in urine in the form of such casts is very important because they tell you where they came from. If you have bacteria in your urine and other signs of infection, presence of WBC casts confirms that the infection is inside your kidneys. If you have no signs of infection, you may have any one of the diseases that can cause inflammation of your kidneys.

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