Urine For AFB (3 Samples)

Function

The Urine for AFB (Acid-Fast Bacilli) test is a specialized microbiological culture and microscopic examination used primarily to detect Mycobacterium tuberculosis within the genitourinary tract. Because the shedding of mycobacteria in urine can be intermittent, three separate early morning samples are typically required to maximize the diagnostic yield.

Why it is Ordered

This test is ordered when a patient presents with symptoms suggestive of renal or urogenital tuberculosis, such as:

• Unexplained hematuria (blood in urine).
• Sterile pyuria (white blood cells in urine without bacterial growth on standard cultures).
• Chronic flank pain or dysuria.
• Systemic symptoms like night sweats, weight loss, and low-grade fever.

Associated Conditions

Extrapulmonary tuberculosis specifically affecting the kidneys, ureters, or bladder is the primary condition associated with a positive result. It may also detect atypical mycobacteria in immunocompromised individuals (e.g., those with HIV/AIDS). Genitourinary TB is often a late manifestation of a primary pulmonary infection that spread via the bloodstream years earlier.