Introduction

Pyuria is defined as the presence of pus in urine. Although sexually transmitted infections (STIs), viral infections, and long-term use of certain drugs are among the leading causes, urinary tract infections (UTIs) are the most frequent. Doctors define pyuria as having a minimum of 10 white blood cells per cubic millimetre (mm3) of urine that has been centrifuged. In rare instances, it may indicate sepsis or a complex UTI. 

Any infection that affects the urinary system is known as a urinary tract infection (UTI). The kidneys, ureters, bladder, and urethra are all parts of the urinary system. The majority of infections affect the bladder and urethra, which are parts of the lower urinary system. If a UTI progresses to the kidneys, it can lead to major health issues. Every year, 8 to 10 million people seek treatment from a healthcare practitioner for a UTI.¹ 

A type of pyuria where no germs are found is called sterile pyuria. In these situations, the cause could be a virus or other form of germ, an undetected bacterium, or an underlying medical problem. Approximately 14% of females and 2.6% of males develop sterile pyuria. Sexually transmitted infections or diseases (STIs or STDs) are frequently the cause of sterile pyuria.² 

Pyuria's diagnostic importance is highlighted by its substantial correlation with UTIs, making it a crucial marker of an active inflammatory response to infection. Clinicians must understand this connection since pyuria helps distinguish between infectious and non-infectious causes of urine symptoms and confirms UTIs. 

Given the high incidence of UTIs in all age groups, from young children to older people, knowing the contribution of pyuria guarantees prompt diagnosis, suitable antibiotic administration, and avoidance of consequences like sepsis or pyelonephritis. This article examines the pathogenesis, clinical implications, and therapy of pyuria in UTIs to guide optimal patient treatment.

Pathophysiology of pyuria in UTIs 

Numerous systems work to prevent bacteria from entering the bladder and upper urinary tract in healthy people. These mechanisms include the majority of germs being washed out of the urethra by urine, bacteria being trapped by mucus-secreting cells in the urethra, and the secretions in the prostate and urethra, which prevent bacterial invasion.

Uromodulin (a protein in the urinary tract), urinary tract epithelial cells, and urea's high osmolality and low pH in the urinary tract all have bactericidal effects.³ Urine cannot ascend into the upper urinary system when the bladder contracts because the junction between the ureter and bladder, called the ureterovesical junction, closes. Bacteria in the distal urethra are prevented from moving upward by the urethral sphincter. To prevent bacterial invasion, the immune system enlists cells like neutrophils, macrophages, and toll-like receptors (TLR4). The potency of the pathogen and the immunological response of the individual determine the capacity to cause infection.

Pyuria is caused by an infection of the urinary system, usually affecting the kidney or bladder. Infections by organisms, including gonorrhoea, chlamydia, tuberculosis, anaerobic bacteria, actinomycosis, fungal infections, and some viral diseases, are a cause of pyuria. Inflammation is the body's response to tissue irritation, leading to swelling, increased blood flow, and white blood cells’ infiltration. Bacterial infections are the most prevalent cause of inflammation. 

Pyuria can also result from inflammatory kidney diseases such as secondary syphilis, glomerulonephritis (inflammation of the tiny filters in the kidneys), analgesic nephropathy (chronic kidney disease caused by long-term use of painkillers), and other conditions like polyarteritis nodosa, lupus nephritis, and lead nephropathy. Moreover, pyuria can also be caused by parasites such as Entamoeba histolytica, Schistosoma haematobium, Giardia lamblia, and Trichomonas vaginalis.^1,4

White blood cell counts in urine are sometimes elevated due to inflammation by bladder or kidney tumours or malignancies. Kidney, ureter, or bladder stones usually cause blood in the urine, but sometimes there may be white blood cells as well. Reiter's syndrome, vaginal contamination, retroperitoneal fibrosis, and chemicals in the bladder or urethra are additional issues to take into account. UTIs, STIs, interstitial cystitis, TB, sepsis, kidney stones, transvaginal surgical mesh, and organ transplant rejection are all prevalent causes of pyuria. 

Over time, medications, such as proton pump inhibitors, diuretics, antibiotics containing penicillin, and nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin, ibuprofen and naproxen sodium, can also cause pyuria.

Clinical presentation

Cloudy urine and pus are indications of pyuria, which frequently has no other symptoms. A spike in white blood cells is usually an indicator in this case. Frequent urination, burning sensation during urination, blood in the urine, foul-smelling urine, pelvic pain, and fever are all signs of a urinary tract infection. Fever, stomach pain, unusual discharge, dysuria, nausea, or vomiting are possible additional symptoms.^1,5

Urinary tract infections can arise in various regions of the urinary tract, each with its specific symptoms as well. Cloudy or crimson urine, lower abdominal pain, and frequent urination are all symptoms of cystitis, a bladder infection. Fever, chills, nausea, vomiting, and side or upper back discomfort are all symptoms of pyelonephritis, an infection of the kidneys. Burning and discharge during urination are symptoms of urethritis, an infection of the urethra.⁷

Diagnostic approach

Doctors usually use three tests to confirm a suspected UTI: urine dipstick, urine analysis, and urine culture. While urine analysis looks for bacteria, blood, or white blood cells, all indicators of a urinary tract infection, the dipstick test is quick and yields immediate results. If the dipstick test comes back negative, but the symptoms persist, a urinalysis is performed. A urine culture is performed to identify the kind of infection by enabling bacteria to proliferate. The bacteria may be screened with various antibiotics.^6,8 

Other tests, including ultrasound, cystoscopic examination, urodynamic studies, intravenous pyelogram (IVP), and CT scan, may be performed by your physician if you frequently get UTIs. These tests help determine whether the infection has migrated to the bloodstream and whether the bladder is functioning normally. If an upper-tract UTI is suspected, blood tests could also be advised.⁷ 

A urinalysis can be used to diagnose pyuria. At a medical professional's office, you will urinate into a particular cup during a urine test. The sample is then sent to a lab, where a lab technician will examine it under a microscope to look for blood, bacteria, and white blood cells.¹

Management of UTIs with pyuria 

Antibiotics or antifungal drugs can effectively treat pyuria caused by infections. If these are ineffective, the illness may have an underlying cause, such as Kawasaki disease (a rare childhood illness that causes inflammation of blood vessels throughout the body). Stopping certain medicines may resolve issues related to prescription drugs. 

Complications from untreated pyuria can include renal damage, organ failure, blood poisoning, and even death. Since many symptoms are mistakenly attributed to inflammation rather than bacterial illness, incorrect diagnoses can make treatment more difficult. Treatment with antibiotics may sometimes worsen the condition. To treat UTIs, medical professionals recommend antibiotics such as nitrofurantoin, sulfonamides, amoxicillin, cephalosporins, doxycycline, and quinolones. Although uncommon, doctors advise using low-dose antibiotics for recurrent UTIs to prevent infection recurrence, since resistance can result in other diseases like Clostridioides difficile infection.^7,9 

Summary

Pyuria, which represents the body's inflammatory reaction to bacterial invasion, is a crucial diagnostic indicator for urinary tract infections (UTIs). Although UTIs continue to be the most frequent cause, pyuria can also result from renal illnesses, medicines, sexually transmitted infections, or other systemic conditions, all of which call for careful assessment. Precise diagnosis by urinalysis, microscopy, and culture guarantees focused therapy, mostly with antibiotics, while addressing underlying causes such as sterile pyuria or STI infection. 

Pyuria must be addressed right away since it can have serious side effects like sepsis or renal damage if left untreated. Reducing UTI recurrence is primarily dependent on preventive measures, including drinking enough water, maintaining good hygiene, and using appropriate antibiotics for recurring infections. To improve patient outcomes, clinicians must remain alert in differentiating between infectious and non-infectious pyuria. Recognising this link enhances the accuracy of diagnosis, facilitates efficient treatment, and reduces risks, underscoring the importance of pyuria in maintaining urinary tract health.