Pyuria refers to the presence of white blood cells and pus in urine, and is commonly seen in individuals with urinary tract infections (UTI). It typically presents with symptoms such as painful urination (dysuria), frequent urination, and urgency.

However, in rare cases, pyuria can occur without any detectable bacteria or obvious cause; this is known as sterile pyuria. When this happens, it may indicate other underlying conditions, one of which is renal tuberculosis (TB). Despite being an important cause, renal TB is often overlooked due to its rarity and the dominance of more common causes like UTIs.

This review focuses on the link between pyuria and renal tuberculosis. It explores the clinical signs, diagnostic approach, underlying mechanisms, and treatment of renal TB, emphasising why patients with pyuria—especially when it's sterile—should be evaluated for this uncommon but important condition.¹

Renal tuberculosis: pathophysiology and epidemiology

Renal tuberculosis is caused by an infection with Mycobacterium tuberculosis that affects the urogenital tract and kidneys. The infection typically begins in the lungs, and the bacteria can later spread to the kidneys through the bloodstream (hematogenous spread). Once in the kidneys, the bacteria lodge in the renal medulla and cortex, triggering a granulomatous inflammation response that leads to progressive tissue damage.^2.

Although renal tuberculosis is a rare case of pyuria in regions with low tuberculosis prevalence, it remains a notable health concern in high-incidence areas.  Renal tuberculosis accounts for 5-15% of all cases of tuberculosis; thus is comparatively less common.³

Clinical presentation of renal tuberculosis

Clinical features of renal tuberculosis vary depending on the stage of diagnosis. Early stages are often asymptomatic, contributing to delayed diagnosis. Most frequently observed clinical signs are:

• Flank pain: Usually dull and intermittent, caused by inflammation or involvement of the renal tissue
• Hematuria: Presence of blood in the urine (microscopic or visible), resulting from damage to the renal parenchyma or granulomatous inflammation
• Dysuria: Painful urination, especially if the bladder is involved
• Fever and night sweats: General constitutional symptoms of tuberculosis
• Malaise and fatigue: Due to the chronic nature of the illness⁴

Patients with advanced illness could have severe renal impairment, i.e., renal abscesses, pyelonephritis, or renal failure⁵. The condition progresses slowly in most patients, and symptoms neither appear nor could possibly be interpreted as other urinary tract infections.

Diagnostic approach to renal tuberculosis

An integrated clinical evaluation alongside several investigative methods is needed to diagnose renal tuberculosis with absent pus, sterile pyuria. Renal tuberculosis patients may present with signs of inflammation. This may be an immune response to the Mycobacterium tuberculosis infection, not due to a bacterial infection.

Urine Analysis: This test constitutes the initial test in most diagnosis protocols. In renal tuberculosis patients, urine indicates leukocytes, proteinuria, and even microscopic hematuria. The urine sample fails to grow any microorganisms on culture, thus the finding of sterile pyuria.

Microscopic Analysis: Microscopy of the urine specimens of patients with far-advanced renal tuberculosis may demonstrate acid-fast bacilli (AFB). Demonstration of AFB on Ziehl-Neelsen staining is not absolutely reliable. This is because the bacterial concentration is very minute in early infections.

Urine Cultures: For conclusive diagnosis, certain cultures like Lowenstein-Jensen medium for Mycobacterium tuberculosis need to be employed, though there is a possibility that M. tuberculosis might not be detected in urine cultures for a few weeks. No positive results on the initial tests do not eliminate the likelihood of the disease.

Imaging Procedures: Imaging Methods: Imaging procedures like ultrasound and CT scans are crucial in diagnosing renal tuberculosis. Ultrasound may demonstrate hydronephrosis, scarring of the kidney, or a renal mass. CT scans are more precise and detect features such as calcifications, atrophy of the kidneys, and abscess formation.⁵

Cystoscopy and Biopsy: If the diagnosis is still not clear, cystoscopy and renal biopsy can be useful. A parenchymal biopsy will probably show the histopathology of granulomatous inflammation typical of tuberculosis.³

Differential diagnosis

Sterile pyuria can be accompanied by a variety of conditions which complicate the diagnostic picture of renal tuberculosis. They are:

Interstitial cystitis: A chronic inflammatory bladder disease that can lead to sterile pyuria in the absence of infection.

Renal calculus: Inflammation and secondary sterile pyuria can result from the irritant effect of a kidney stone.

Malignancy: Sterile pyuria can be a sign of malignancies like urothelial carcinoma or other incapacitating malignancies of the urogenital tract, necessitating further evaluation.

Non-tuberculous infection: Silent fungal or viral infections are occasionally linked with sterile pyuria, but are uncommon.⁶

Treatment of renal tuberculosis

Renal tuberculosis can be treated with a combination of anti-tuberculosis chemotherapy and, in some instances, surgery. Recommended treatment of tuberculosis involves a combination of first-line drugs as follows:

• Isoniazid (INH)
• Rifampicin
• Ethambutol
• Pyrazinamide

Duration of the course of treatment ranges from six and nine months, depending on disease severity and clinical response of the patient. Directly observed therapy (DOT) is frequently advocated to enhance compliance and decrease resistance to drugs.⁶

In advanced renal tuberculosis, surgical intervention could be necessary to manage complications like renal abscess, diffuse calcification, or obstructive uropathy. Nephrectomy can be undertaken in extensive renal destruction or failure of medical therapy.²

Conclusion

Renal tuberculosis is a significant but unusual cause of sterile pyuria, especially in areas where tuberculosis is more common. Although the clinical presentation is not specific and the diagnosis is difficult, a high suspicion of the disease should exist in patients presenting with risk factors or pyuria for which no aetiology can be identified. Early treatment with appropriate management can prevent further renal injury and also improve the outcome in the patient. The doctor should also keep in mind renal tuberculosis as a possible explanation for sterile pyuria to give early treatment and not mistake it for another disorder

Frequently asked questions

What is pyuria?

Pyuria is the presence of white blood cells in the urine, indicating inflammation or infection in the urinary tract.

What is renal tuberculosis?

Renal tuberculosis is a form of extrapulmonary tuberculosis that affects the kidneys and urinary tract.

What are the symptoms of renal tuberculosis?

Common symptoms include flank pain, hematuria, pyuria, and frequency of urination.

How is renal tuberculosis diagnosed?

Diagnosis involves a combination of laboratory tests (e.g., urine culture, AFB smear), imaging studies (e.g., ultrasound, CT scan), and biopsy.

What is the treatment for renal tuberculosis?

Treatment involves antitubercular therapy (ATT) with a combination of first-line drugs, and surgery may be necessary to relieve obstruction or repair damaged tissue.

Summary

Renal tuberculosis is a treatable condition that can cause sterile pyuria. Prompt diagnosis and treatment are crucial to prevent long-term kidney damage. Healthcare providers should consider renal tuberculosis in the differential diagnosis of sterile pyuria, especially in high-risk populations. Early intervention can improve patient outcomes and quality of life.