What Is Pyuria

  • Jialu Li Master of Science in Language Sciences (Neuroscience) UCL

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Testing your urine (pee) can unravel many things about your health as any changes in the colour, smell, or the substances present in the urine can indicate a specific condition related to health problems. One of these conditions is called pyuria where white blood cells (special cells that protect us from infections) are seen in your urine and can be indicative of many illnesses, the most common are bladder infections. In this article you will learn more about pyuria and sterile pyuria, how it is diagnosed, and what causes it.

What is Pyuria?

A condition in which pus (a yellowish, thick fluid produced when the body is fighting off infections) and white blood cells (a special type of blood cells that protect us from infections) are found in your urine. Your doctor diagnoses pyuria by asking you to provide a urine sample for testing. Although pyuria itself is not a disease, it is caused by many diseases that must be identified and treated.1

How is pyuria diagnosed?

Your doctor will likely ask for a special urine test, called urinalysis, to be done. In this case, you will be asked to provide a urine sample that must be immediately taken to the lab to be tested.

What is a urinalysis?

Testing the urine can help the doctor diagnose many diseases related to the urinary tract or other illnesses such as diabetes and liver diseases.2 Urinalysis is a commonly used test where lab specialists do the following:

Macroscopic examination

Lab specialists will observe any changes to the ordinary colour of the urine sample:

  • Cloudy urine might indicate infection or a diet high in protein
  • Red colour might indicate blood in the urine or eating certain foods such as beats.
  • Green/blue colour might indicate infection or the use of certain medications

Also, certain unusual smells are related to specific conditions:

Microscopic examination

The lab specialists will place a drop of urine on a glass slide to look at it under the microscope where they look for the presence and count of:

  • Red blood cells: The presence of three red blood cells or more in the urine indicates a condition called hematuria (blood in urine), which is associated with many health conditions (e.g. kidney problems, cancers, infection, etc.)
  • White blood cells: The presence of low numbers of white blood cells (<2 in men and <5 in women) is considered normal, but higher numbers can indicate several health conditions (e.g. infection, inflammation, kidney problems, etc.)
  • Crystals: crystals form when there is an excess of certain minerals in the urine that accumulate together to form a big mass. There are different types of crystals that indicate different conditions (e.g. dehydration, infection, kidney disease, etc.)
  • Bacteria: urine should be sterile (does not contain any bacteria), and the presence of bacteria points to infection3

Urine dipstick test

This is a rapid test that takes a few seconds to a few minutes to complete. The test uses a special paper stick that has small coloured squares each one is treated with a specific chemical.

Once the dipstick is dipped in the urine sample, the substances in the urine sample interact with the chemicals in the dipstick and produce colours. These colours are then compared to a chart to see what chemicals are present in your urine. The darker the colour, the more of that substance is in the urine. For example, the dipstick might detect the presence of:

  • Protein
  • Sugar (glucose)
  • Red blood cells
  • White blood cells
  • Nitrite
  • Ketone

These are not normally found in urine and their presence indicates different conditions.2,3

How is pyuria identified?

Pyuria is identified when one of these is seen in a urinalysis:

  • Ten or more white blood cells in one cubic millimetre (one microlitre) of the urine sample
  • Three or more white blood cells seen under the microscope
  • The urinary dipstick test is positive for leukocyte esterase; an enzyme that is produced by white blood cells and its presence in the urine suggests the presence of white blood cells1

What is sterile pyuria?

When the healthcare provider sees white blood cells in the urine but no bacteria, it is called sterile pyuria. In the lab, after the urine is tested with a microscope and dipstick, lab specialists would culture the urine on special media containing nutrients to support bacteria growth. When pyuria is found in a urinalysis, but no bacteria grows when the urine is cultured, it is called sterile pyuria.2

What causes pyuria/sterile pyuria?

Infections

The most common cause of pyuria is infection of the bladder and less commonly of the kidney, whereas sterile pyuria could be caused by infectious or non-infectious diseases.1,4

Signs and symptoms

In the case of bladder infection, you might experience the following:

  • · Burning sensation when urinating
  • · Having to frequently urinate
  • · Feel the need to urinate even when your bladder is empty
  • · Blood in the urine

In the case of kidney infection, you might experience the following:

  • · Fever and chills
  • · Nausea
  • · Vomiting
  • · Lower or side back pain

Urinary tract infections (UTIs)

Urinary tract infections (UTIs) are the most common cause of pyuria. These infections occur when the skin or rectal bacteria reach the urethra and then the bladder causing bladder infection (cystitis), which is the most common UTI. These bacteria can also infect the kidneys causing kidney infection (pyelonephritis), which is a rarer but more serious infection. 

Treatment

If you are diagnosed with a UTI, your doctor will prescribe you an antibiotic.

Sexually transmitted infections (STIs)

These can be responsible for sterile pyuria, as many bacteria that cause STIs cannot grow, or grow very slowly, on the culture media typically used in labs, also viruses and parasites that cause STIs cannot grow on bacterial media.4 Some of the STIs are:

Chlamydia

Chlamydia is an STI caused by a bacteria called Chlamydia trachomatis that can be transmitted through sexual encounter (vaginal, oral, or anal) with an infected partner without the use of protection (i.e. condoms). Although curable, chlamydia can cause serious damage to the female reproductive system if not detected and treated.

Signs and symptoms

Most cases of chlamydia are asymptomatic, but when symptoms occur women might have:

  • Burning sensation when urinating
  • Irregular vaginal charge

And men might have:

  • Burning sensation when urinating
  • Discharge from the penis
  • Swelling in one or both testicles

Treatment

Chlamydia is curable, and the doctor will prescribe you antibiotics that both you and your sexual partner should take.

Trichomoniasis

Also known as “trich”, is an STI caused by a parasite called Trichomonas vaginalis and it is transmitted through having unprotected sex with an infected partner. In infected pregnant women, it can cause early delivery of the baby, and the newborn might have a low weight at birth.

Signs and symptoms

Almost 70% of infected people will have no symptoms. Symptomatic women might experience:

  • Itching and redness in the genital areas
  • Discomfort when urinating
  • Vaginal discharge that can be white, yellow, or green in colour with a fishy smell

Symptomatic men might experience:

  • Penis discharge
  • Burning sensation after urinating or ejaculating
  • Itching in the penis

Treatment

Trichomoniasis is curable with medication. Your doctor will prescribe an antibiotic that both you and your sexual partner should take.

Other STIs

Other STIs include:

Systemic conditions

Systemic Lupus Erythematosus (SLE)

Systemic Lupus Erythematosus (SLE) is a common type of lupus, which is an autoimmune disease where the immune system (normally helps in the defence against infection) starts to attack your own tissues causing inflammation and damage. The causes of SLE are unknown.

Signs and symptoms

Signs vary but people might experience:

  • Fever
  • Fatigue
  • Rashes
  • Joint pain and swelling

Treatment

SLE cannot be cured but can be managed using immunosuppressive drugs (drugs that inhibit your immune system activity) such as corticosteroids (e.g. prednisone).

Kawasaki disease (KD)

Kawasaki disease (KD) causes inflammation (swelling and redness) in the body’s blood vessels, and it mainly affects children under the age of 5. If not treated, it can cause heart complications that can be deadly.

Signs and symptoms

Your child would have a high fever for more than 5 days accompanied with one or more of the following:

  • Rash
  • Red eyes
  • Swelling in the nick
  • Redness inside the mouth and the back of the throat
  • Swelling and redness in the hands
  • Swelling and redness in the tongue giving it a “strawberry” look

Treatment

The doctor would prescribe:

  • Aspirin (never give aspirin to a kid under the age of 16 without a doctor’s prescription as this could lead to a deadly condition called Reye’s syndrome)
  • Intravenous immunoglobulin, which is a mix of antibodies (proteins the body makes to fight infection) taken from healthy donors and injected through the vine.

Other conditions

  • Kidney diseases and cancers
  • Pregnancy
  • Diabetes
  • Certain medications

FAQ’s

How can I prepare for a urinalysis?

Your healthcare provider will give you a special, sterile cup to urinate (pee) in.

Normally, a doctor might ask for what is called a midstream specimen for urine (MSU). In this case, you pass the first part of urine in the toilet, then you open the sterile container and collect enough volume of urine from the midstream flow, and then you remove the cup and finish peeing.

The specimen should be assessed immediately, so you should deliver it to the surgery or lab as soon as possible, preferably within two hours.

Is the presence of pyuria in urine tests enough to make a diagnosis?

No, your healthcare provider might ask for further tests to confirm the condition that caused your pyuria to decide what the best management and/or treatment is.

Can pyuria be transmitted from person to person?

No, but the sexually transmitted infections (STIs) that might have caused the pyuria can be transmitted from person to person.

How to prevent UTIs?

You can prevent urinary tract infections by:

  • Urinate after sex
  • Stay hydrated
  • Limit the use of douching, sprays, and powders to the genital area
  • Females should wipe front to back after using the toilet

How to prevent STIs?

You can prevent sexually transmitted infections by:

  • Use condoms
  • Limit the number of sexual partners
  • Be in a mutual monogamy sexual relationship with an uninfected partner

Summary

Pyuria is a condition in which white blood cells are found in a urine sample indicating an infection. The most common cause is urinary tract infections (UTIs). In this case, the lab specialist will find bacteria when they culture urine on special media that grow bacteria. When bacteria cannot be found, the condition is then called sterile pyuria. Sterile pyuria can indicate a sexually transmitted infection (STI) caused by bacteria, viruses, or parasites, and it can also be caused by other non-infectious diseases (e.g. autoimmune diseases, kidney problems, etc.), or some medication. The healthcare provider will mostly ask for further testing to diagnose the underlying cause of pyuria before prescribing treatment.

References

  • Wise GJ, Schlegel PN. Sterile pyuria. N Engl J Med. 2015 Mar 12;372(11):1048-54. doi: 10.1056/NEJMra1410052. 
  • InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Understanding urine tests. 2010 Jul 27 [Updated 2019 Oct 24]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279350/
  • Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician. 2005 Mar 15;71(6):1153-62. Erratum in: Am Fam Physician. 2006 Oct 1;74(7):1096.
  • Glen P, Prashar A, Hawary A. Sterile pyuria: a practical management guide. Br J Gen Pract. 2016 Mar;66(644):e225-7. doi: 10.3399/bjgp16X684217. 

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Farah Hamdan

M.Sc. in Infection Biology, M.Sc. in Clinical Laboratory, B.S. in Pharmacy and Pharmaceutical Chemistry, Tishreen University

I am interested in infectious diseases and in studying the microorganisms causing them. I have years of experience teaching university students different health-related topics, and now, I aspire to transfer this knowledge to the public in a simple, clear way.

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