Renal tuberculosis is one of the most common forms of extrapulmonary infection by Mycobacterium tuberculosis, usually developing as a result of hematogenous dissemination from the lungs. Hematuria, nocturia, and abdominal or pelvic pain are main symptoms. The diagnosis is made through a comprehensive clinical assessment, urinalysis, and imaging studies such as abdominal ultrasonography, invasive renal procedures, and computed tomography, whereas microbiological studies - cultivation, or polymerase chain reaction (PCR) testing, is necessary as well.
With approximately 9 million new cases being diagnosed each year, tuberculosis is globally an important disease that is primarily causing infections in the African and Asian continents, and only a minority of patients are from Europe and the United States of America  . Apart from pulmonary tuberculosis, many extrapulmonary forms of the disease have been described in the literature, and one of the most important and most common is renal tuberculosis, comprising from 15%-27% of all extrapulmonary cases   . The pathogenesis stems from hematogenous spread of M. tuberculosis from the lungs to the kidneys, often in the absence of symptoms that could suggest an ongoing process in the pulmonary system . After a variable incubation period, the clinical presentation of renal tuberculosis resembles a urinary tract infection (UTI) - dysuria, nocturia, pain in the flank, abdomen, or pelvis    . Hematuria, appearing as an isolated symptom, is an important clue toward renal tuberculosis, but it may also be accompanied by proteinuria and sometimes pyuria   . Typical symptoms encountered in pulmonary tuberculosis, such as fever, weight loss, and night sweats are uncommon . However, more severe infections can lead to marked kidney damage, resulting in obstructive uropathy and loss of kidney function that progresses to renal failure and end-stage renal disease   . For this reason, an early diagnosis is vital.
With a properly obtained patient history and a detailed physical examination, sufficient evidence may be obtained to pursue a diagnosis of renal tuberculosis. As immunosuppression is one of the main risk factors for an infection by M. tuberculosis, patients should be asked about underlying illnesses (for example, human immunodeficiency virus infection, transplantation, dialysis, etc.) , but also if they already suffered from tuberculosis, since about 25% of cases were previously diagnosed with pulmonary tuberculosis . After assessing the presence of signs and symptoms that are further evaluated during the physical examination, a full laboratory workup and urinalysis should be performed. In addition to hematuria and proteinuria, sterile pyuria is a hallmark of tuberculosis, in which case more advanced microbiological studies are necessary. Acid-fast staining (by using Ziehl-Neelsen stain) and cultivation of at least three urine samples obtained in the morning on the Lowenstein-Jensen medium are highly successful methods for detecting M. tuberculosis, yielding a positive rate of up to 95%   . But as mycobacteria grow very slowly on these media, approximately 6-8 weeks need to pass before a definite diagnosis can be made, which is why more advanced methods that detect bacterial DNA (like PCR) are often used . Imaging procedures (ultrasonography, computed tomography, magnetic resonance imaging, intravenous urography, chest X-rays) are equally important for assessing the status of the kidneys and potentially reveal any pathological lesions     .