Pyuria, Key Facts:

• Pus in urine (pyuria) is typically caused by infections in the urinary tract.
• Pyuria is defined as the presence of more than 10 white blood cells in a urine sample under a microscope.
• Non-sterile pyuria is caused by urinary tract infections, while sterile pyuria has no detectable bacterial cause.
• Causes of sterile pyuria are classified into infectious and non-infectious causes.
• Pus in urine may not necessarily make urine turbid or unclear.
• Symptoms of pyuria include pain during urination, frequent urination, sudden urge to pee, and bladder or kidney pain.
• The most important treatment of pus in urine is treating the underlying cause.

What is Pyuria?

Definition of pyuria:

Pus (generally) is a slightly thick and opaque fluid formed in the infected tissues. Its color is typically whitish-yellow or greenish.

Pus is typically formed of dead white blood cells, bacteria, and dead tissues.

Regarding pus in the urine, we define it as the presence of more than 10 white blood cells (WBCs) in a centrifuged urine sample under the microscope high power field.

Non-sterile V.S. sterile pyuria:

Pyruia (Pus in urine) is usually a sign of infection and is associated with positive urine culture tests in cases of UTI.

However, some people may have pus in their urine with a negative culture test. A condition called (sterile pyuria (reference).

The causes of both non-sterile and sterile pyuria (pus in urine) are discussed in the next section.

Pyuria doesn’t necessarily mean Turbid or unclear urine:

Pus in urine (pyuria) may be undetectable grossly by your eyes. Mild cases of pyuria (with only a few pus cells) may be found in a clear urine sample.

So, pyuria is not defined according to the appearance of urine but according to urine examination by a microscope.

What causes pyuria?

Pus in urine is mainly caused by UTI (Non-sterile Pyuria):

Pus in urine is mainly caused by urinary tract infections (uncomplicated or complicated). Moderate to severe cases of pus in urine cause urine to become turbid (opaque, yellowish, grayish, or greenish turbid urine).

UTI is a very common urinary tract disease, especially in females (due to shorter urethra making it easier for the bacteria to enter the urinary tract).

Sterile Pyuria (Pus in urine with a negative culture test).

Sterile pyuria is also common. It affects about 13.9% of women and 2.6% of men (reference).

Sterile pyuria (pus in urine without detectable bacterial cause by a standard culture test) results from a wide variety of causes.

The causes of sterile pyuria are classified into:

• Infectious causes: bacteria, viruses, or fungi that aren’t detectable by standard culture methods.
• Non-infectious causes: such as stones, tumors, irritation of the urinary tract, etc.

The most common causes of sterile pyuria are:

1. The recent treatment of urinary tract infection.
2. Recent antibiotic use.
3. Kidney stones.
4. Sexually transmitted infections such as gonorrhea and chlamydia infection.
5. Viruses such as genital herpes and herpes zoster.
6. Interstitial cystitis.
7. Fungal urinary tract infections.
8. Urinary tract TB.
9. Sepsis and severe infections such as pneumonia.
10. Other less common diseases include legionella, leptospira infections, sarcoidosis, and IgG-4-related disease.
11. Urinary tract tumors, and others (learn more).
12. Recent use of a urinary catheter or recent procedures such as cystoscopy.

How serious is pus in urine?

Pus in urine is common with both simple and complicated and serious urinary tract diseases. For Instance, simple infections such as acute cystitis may cause pyuria that usually resolves with treatment.

The degree of pus in urine may reflect the severity of the disease. The human eye does not detect mild pus in the urine, while moderate and severe cases appear as turbid urine.

The degree of pyuria is correlated with the degree of turbidity. The more turbid is urine, the more likely the condition is severe.

Also, combined blood and pus in urine may reflect a more serious conditions such as complicated urinary stones or malignancy.

Symptoms of pyuria and how does it look?

Pyuria (pus in urine) is a symptom or sign, not a separate disease. Pus in urine has different looks according to its severity, associated conditions, and the presence of coexisting blood (hematuria).

The appearance of pus in urine:

Possible appearances of pyuria

• Greyish or greyish-yellow turbid urine.
• Tiny whitish or greyish speckles or strings in urine.
• White debris in a urine sample.
• Tubrid greyish-brown or reddish urine (combined pyuria and blood in urine).
• Normal-looking urine (pus is only detectable in urine analysis).

Common symptoms associated with pyuria:

The most common cause of pus in urine is UTI (urinary tract infection). Common symptoms of UTI associated with pyuria include:

• Pain during urination (dysuria).
• Frequent urination (small amounts of urine, which may be turbid due to the presence of pus).
• Sudden urge to pee.
• Pink or reddish urine (due to blood in urine).
• Bladder (lower abdominal) or kidney (flank) pain.
• Sometimes, fever and chills.
• Nausea, anorexia (loss of appetite).

Symptoms of other diseases that may be associated with pus in urine:

• Renal stones: flank or loin pain, passing a stone, blood in urine, etc.
• Sexually transmitted diseases: Urethral pain, urethral discharge (pus or bloody) without urination, genital ulcers, etc.
• Concomitant history of a disease known to cause pus in the urine, such as interstitial cystitis, recent catheter insertion, bladder cancer, prostatitis, etc.

Diagnosis.

• Urine culture and sensitivity: It is the most commonly used test to diagnose the cause of pus in the urine. Typically, most cases of pus in urine are due to UTI and have positive culture tests.

If the culture and sensitivity testing is negative, the condition is called sterile pyuria, and your doctor will often perform a thorough clinical history and examination. Also, your doctor will typically need to perform more advanced investigations, such as:

• Testing for STIs (sexually transmitted infections).
• Testing for Urinary tract Tuberculosis (T.B)
• Testing for Fungal UTI (Fungi may cause pus in urine that is distinguishable from bacterial UTI).
• And others.

Treatment of pus in the urine

The most important treatment of pus in urine is the treatment of the cause. Once the cause is cleared, pus will typically resolve subsequently. The table below lists the common causes of pus in urine and their treatments (reference).

CAUSE	TREATMENT
1. UTI	Antibiotics for 3 to 5 days (such as Nitrofurantoin or Fosphomycin) or according to the culture and sensitivity test.
2. Urinary tract stones	Stone extraction or lithotripsy.
3. Urinary tract T.B	3 to 6 months of anti-tuberculous drugs such as Rifampin, Isoniazid, ethambutol, and pyrazinamide.
4. STIs (Gonorrhea or chlamydia)	Antibiotics such as ceftriaxone, azithromycin, and doxycycline.
5. Mycoplasma and ureaplasma infections	Antibiotics such as Azithromycin or levofloxacin.
6. Genital herpes	Antiviral drugs such as Acyclovir.
7. Fungal Infections	Antifungal medications such as fluconazole, posaconazole, etc.
8. Trichomoniasis	Metronidazole or tinidazole.

FAQs about Pyuria:

Can A kidney stone cause pus in urine?

Yes, A kidney stone can cause pyuria (pus in urine). It may cause pus through the predisposition of UTI (non-sterile pyuria). Also, it may cause sterile pyuria (pus in urine without evidence of UTI).

What is the normal range of pus cells in urine?

The normal range of pus cells in urine is 0-3 pus cells per high power field (HPF) of microscopy. The presence of 4 or greater pus cells in urine analysis is considered pyuria (even if your urine appears clear).

What does it mean to have pus cells in urine 10-20, 20-30, or more?

Pus cells greater than 4 cells per high power field typically means pyuria. The most common cause of pyuria is urinary tract infections (UTIs). So, if you have pus cells of 10, 20, 30, 40, or even 100 cells/HPF, a urine culture and sensitivity testing is usually the next step to confirm or exclude UTI.

Does pus in urine mean UTI?

Pus is formed of white blood cells (neutrophils), and it is usually due to bacterial infection (UTI). However, some other conditions (atypical bacteria, viruses, fungi, and non-infectious causes) may cause pus in the urine. So, pus in urine doesn’t always mean UTI.