24-Hour Sputum AFB Test (Acid-Fast Bacilli)

The Sputum AFB test is the primary diagnostic test for active pulmonary tuberculosis (TB). It detects Acid-Fast Bacilli — primarily Mycobacterium tuberculosis — in sputum through Ziehl-Neelsen microscopy. It is also used to monitor TB treatment response by checking whether the bacteria are clearing from sputum over the course of anti-TB therapy.

Sputum must come from a deep cough — not saliva from the mouth. Take a deep breath, hold for a moment, then cough deeply to bring up mucus from the lungs. Collect in the clean, sealed container provided by Medall. An early morning specimen (first cough of the day) has the highest bacterial concentration. Your Medall team will provide specific collection instructions.

The 24-hour protocol typically involves two or three samples collected over 24 hours — a spot specimen at the time of first visit, an early morning specimen the next day (overnight accumulation provides highest yield), and sometimes a second spot. Multiple samples improve detection sensitivity for TB, which may be shed intermittently.

Smear microscopy results are typically ready within 6–12 hours of sample receipt. Culture results (if ordered) take 4–8 weeks for standard solid medium or 2–4 weeks for liquid culture (MGIT). Rapid molecular tests (GeneXpert) results are available within 4 hours.

Yes. AFB smear sensitivity is approximately 40–70%. A negative smear does not exclude TB if clinical suspicion remains high. Further testing — sputum culture, GeneXpert/CBNAAT, or imaging — may be needed. Physicians follow a clinical-microbiological approach and treat TB empirically in high-risk patients even with initial negative smears.

Active pulmonary TB is transmitted through infectious airborne droplets from coughing or sneezing. While awaiting test results, individuals with TB symptoms (productive cough > 2 weeks, haemoptysis, fever, night sweats) should take sensible precautions — wear a surgical mask, avoid crowded enclosed spaces, and ensure good ventilation. Once treatment is started, infectiousness reduces dramatically within 2–4 weeks.

Book online at medall.in, through the Medall app, by calling +91 7550 177 777, or via WhatsApp. The AFB test requires a sputum sample — your Medall team will provide collection instructions and a specimen container. S5 — MOST BOOKED TESTS AT MEDALL Most Booked Tests at Medall Trusted by millions of patients across South India — these are the tests our doctors recommend most. Test Price Description Complete Blood Count (CBC) ₹X/* Screens for anaemia, infections, and immune health Thyroid Profile (T3, T4, TSH) ₹X/* Detects hypothyroidism, hyperthyroidism, and thyroid disorders HbA1c — Diabetes Monitoring ₹X/* 3-month average blood sugar — essential for diabetes management Liver Function Test (LFT) ₹X/* Complete liver health panel including ALT, AST, Albumin, Bilirubin & more [View All Popular Tests →]