What is the cause of pyuria (presence of pus in the urine)?

From the Guidelines

Pyuria is a common finding that indicates inflammation in the urinary tract, and its management should prioritize the prevention of long-term sequelae such as renal scarring and hypertension, as evidenced by the most recent study 1.

Definition and Diagnosis

Pyuria refers to the presence of white blood cells (WBCs) in the urine, typically defined as more than 5-10 WBCs per high-power field on microscopic examination. It is a common finding that indicates inflammation in the urinary tract. The most frequent cause of pyuria is urinary tract infection (UTI), where bacteria trigger an immune response leading to WBC accumulation. To diagnose pyuria, a urinalysis is performed, often followed by a urine culture to identify specific pathogens.

Treatment and Management

Treatment depends on the underlying cause, with antibiotics like nitrofurantoin (100mg twice daily for 5-7 days), trimethoprim-sulfamethoxazole (one double-strength tablet twice daily for 3 days), or ciprofloxacin (250mg twice daily for 3 days) typically prescribed for bacterial UTIs. However, pyuria can also occur in non-infectious conditions such as kidney stones, interstitial cystitis, or as a side effect of certain medications. Sterile pyuria—where WBCs are present but no bacteria are cultured—may require further investigation to identify causes like partially treated infections, tuberculosis, or inflammatory conditions.

• Patients with pyuria should increase fluid intake, complete the full course of any prescribed antibiotics, and follow up if symptoms persist despite treatment.
• High-risk patients, including those with a prior history of pyelonephritis, lack of response to therapy, diabetes, anatomic or congenital abnormalities of the urinary system, infections by treatment-resistant organisms, or nosocomial infection, require close monitoring and aggressive treatment to prevent complications 1.
• The role of imaging in pyuria is to guide treatment by identifying patients who are at high risk to develop recurrent UTIs or renal scarring, as noted in the study 1.

Key Considerations

• The relationship between childhood UTIs, vesicoureteral reflux (VUR), and renal scarring is complex and not completely understood, with studies suggesting that pyelonephritis and renal scarring can occur without VUR 1.
• The incidence of acute pyelonephritis in the absence of documented VUR is high, and previous episodes of pyelonephritis or VUR increase the risk for recurrent pyelonephritis 1.
• The management of pyuria should prioritize the prevention of long-term sequelae such as renal scarring and hypertension, as evidenced by the most recent study 1.

From the Research

Definition and Diagnosis of Pyuria

• Pyuria is often used as an important marker in the diagnosis of urinary tract infection 2
• The interpretation of pyuria may be especially important in patients with nonspecific complaints 2
• Pyuria is defined as the presence of white blood cells in the urine, which can be an indicator of infection or inflammation in the urinary tract 3

Association with Urinary Tract Infections

• Pyuria is a useful indicator of urinary tract infection among patients with compatible symptoms 3
• However, its utility has not been adequately investigated among patients with acute nephrolithiasis 3
• The presence of pyuria is associated with an increased risk of urinary tract infection, especially in patients with certain clinical characteristics such as dysuria, frequent urination, and chills 3

Clinical Characteristics and Outcomes

• Patients with urinary tract infection more often have a history of dysuria, frequent urination, chills, urinary tract infection, or subjective fever 3
• Pyuria has only a moderate accuracy in identifying urinary tract infection in patients with acute nephrolithiasis 3
• Frequent pyuria or urinary tract infection episodes are associated with increased risks of renal outcomes, including end-stage renal disease, rapid renal function progression, and all-cause mortality 4

Treatment and Management

• Antibiotics targeted toward Escherichia coli, Proteus, Klebsiella, and Staphylococcus saprophyticus are the recommended treatment for urinary tract infections 5
• The duration of treatment varies by specific drug and type of infection, ranging from 3 to 5 days for uncomplicated cystitis to 7 to 14 days for pyelonephritis 5
• Extended release ciprofloxacin at a dose of 1,000 mg once daily was as safe and effective as conventional treatment with 500 mg ciprofloxacin twice daily for adults with complicated urinary tract infections or acute uncomplicated pyelonephritis 6