Urine For A.F.B
- Sample Type
- Urine
- Fasting
- No
- Unit
- Qualitative
Function
The Urine for Acid-Fast Bacilli (AFB) test is a laboratory procedure used to detect mycobacteria, most notably Mycobacterium tuberculosis. Mycobacteria have a unique waxy cell wall that resists traditional staining; however, they retain red dyes even after being washed with acid (hence 'Acid-Fast'). This test typically involves a smear (microscopic exam) and a culture.
Why it is Ordered
This test is ordered when a doctor suspects Genitourinary Tuberculosis (GUTB). Symptoms might include blood in the urine (hematuria), frequent urination, or pain during urination that does not respond to standard antibiotics. It is particularly indicated if a patient has 'sterile pyuria'—the presence of white blood cells in the urine without a standard bacterial infection.
Associated Conditions
- Genitourinary Tuberculosis: Infection of the kidneys, ureters, or bladder by M. tuberculosis.
- Systemic Tuberculosis: Disseminated TB that has spread to the renal system.
- Nontuberculous Mycobacteria (NTM) Infections: Infections by other species of mycobacteria that are not TB but are still acid-fast.
Why Context Matters
A single urine sample has low sensitivity because mycobacteria are shed into the urine intermittently. It is standard practice to collect three consecutive early-morning midstream urine samples to increase the likelihood of detection. Contamination with smegma (which contains commensal Mycobacterium smegmatis) can sometimes cause false-positive smears, though cultures usually clarify this.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Urine For A.F.B:
Official Sources
Research & Guidelines
- PubMed: Urine For A.F.B Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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