Which statement about acid-fast bacillus smear in TB evaluation is true?

• A. It is the most definitive test
• B. It is a presumptive test and can become contaminated
• C. Used to confirm drug Susceptibility
• D. Has no false positives

Answer: (B)

The acid-fast bacillus smear is a rapid screening tool used to detect mycobacteria in specimens, but it does not prove TB on its own. It’s best described as a presumptive test because a positive smear suggests mycobacterial presence but cannot distinguish M. tuberculosis from non-tuberculous mycobacteria and gives no information about drug susceptibility. Because of these limitations, positive smears must be followed by culture and susceptibility testing to confirm the diagnosis and guide therapy. There’s also a risk of contamination or technical issues during collection and processing that can affect the result, so smear findings should be interpreted in the context of clinical presentation, radiography, and subsequent culture results.