What does a positive acid fast bacillus smear mean?
Positive AFB smears indicate a probable mycobacterial infection. However, a culture must be performed to confirm a diagnosis and identify the species of mycobacteria present.
What can cause a positive AFB?
A positive AFB smear resulting from other bacteria that may have a positive AFB smear, such as Nocardia, Actinomyces, Rhodococcus, Legionella micdadei or cysts of Cryptosporidium species (12, 13).
What is acid-fast positive bacteria?
Acid-fast bacteria, also known as acid-fast bacilli or simply AFB, are a group of bacteria sharing the characteristic of acid fastness. Acid fastness is a physical property that gives a bacterium the ability to resist decolorization by acids during staining procedures.
What disease is suspected if a sputum sample is positive for acid-fast staining?
Sputum, or phlegm, is often used to test for Mycobacterium tuberculosis, to find out if a patient has TB. This bacterium is completely acid-fast, which means the entire cell holds onto the dye. A positive test result from the acid-fast stain confirms the patient has TB.
What the causes of false positive acid-fast smears?
Exposure to direct sunlight and the excessive heat can also destroy a significant number of acid-fast bacilli in the sputum sample, thereby rendering the results compromised. Analytical factors such as poor smearing, staining, and microscopy can also hamper the results of acid-fast microscopy.
What diseases are diagnosed using acid-fast procedure?
An acid-fast bacteria (AFB) culture is done to find out if you have tuberculosis (TB) or another mycobacterial infection. Besides TB, the other main mycobacterial infections are leprosy and a TB-like disease that affects people with HIV/AIDS.
Does AFB positive mean TB?
If your AFB culture was positive, it means you have active TB or another type of AFB infection. The culture can identify which type of infection you have. Once you have been diagnosed, your provider may order a “susceptibility test” on your sample.
How is acid-fast bacilli treated?
The standard treatment for TB comprises an intensive phase with isoniazid, rifampicin, pyrazinamide, and ethambutol for 2 months, followed by a continuation phase that comprises the concomitant use of isoniazid and rifampicin for another 4 months. This standard treatment is highly effective for drug-susceptible TB.
What is the principle of acid-fast bacilli?
The mycobacterial cell wall contains mycolic acids, which are fatty acids that contribute to the characteristic of “acid-fastness.” The principle of the AFB smear is based on the fact that mycolic acid in the cell wall of AFB render them resistant to decolorization with acid alcohol.
What is the importance of acid-fast staining?
The acid-fast stain is a laboratory test that determines if a sample of tissue, blood, or other body substance is infected with the bacteria that causes tuberculosis (TB) and other illnesses.
What are the reasons for having a false positive and false negative results during acid-fast staining?
False-negative results can result from: Smears that are too thick. Smears that are too thin. Poor staining technique.
What are two well known human diseases that are caused by acid-fast bacteria?
TUBERCULOSIS, LEPROSY AND OTHER DISEASES CAUSED BY ACID-FAST BACTERIA.
How long does it take for an acid fast bacillus smear test?
Acid-fast bacillus (AFB) is a type of bacteria that causes tuberculosis (TB) and other infections. AFB tests look for AFB bacteria in sputum. An AFB smear test gives results in 1–2 days but can’t confirm a diagnosis. An AFB culture can confirm a diagnosis, but results take 6–8 weeks. Learn more.
When to discontinue sputum acid fast bacillus?
Once a patient has been diagnosed with TB, “isolation should be discontinued only when the patient is on effective therapy, is improving clinically, and has had 3 consecutive negative sputum acid fast bacillus (AFB) smear examinations collected on different days” (3).
How are acid fast Bacilli ( AFB ) smears are classified?
Laboratory Examination: Acid-Fast Bacilli (AFB) Smears (2) Negative smears do not exclude TB disease. When acid-fast bacilli are seen in a smear, they are counted. According to the number of acid-fast bacilli seen at a certain magnification, the smears are classified as 4+, 3+, 2+, or 1+. The greater the number the more infectious the patient.
What are the sensitivity of sputum AFB smears?
Sputum AFB smears and culture results for M. tuberculosis are shown in Table Table1.1. Sputum AFB smears had a sensitivity of 67.5% (95% CI, 60.6 to 73.9) and specificity of 97.5% (95% CI, 97.0 to 97.9) when the data from the two hospitals were combined.