Acid fast bacteria retain the stain even after washing with acid, hence confirming the presence of acid fast bacilli such as Mycobacterium.
What is Sputum AFB test and why is it done?
It is usually the first diagnostic method used when TB infection is suspected.
AFB stands for Acid Fast Bacilli, which are, the bacilli that retain stain even after washing with acid, hence showing ‘acid- fastness’
The bacterium that causes TB is Mycobacterium tuberculosis (MTB), which is an acid fast bacterium.
The stain that is used for detection of MTB is Ziehl-Neelsen (ZN) stain.
This test is called Sputum AFB test because sample used in this test is sputum of the infected individual.
How is Sputum AFB done?
Following is the procedure for Sputum AFB test:
Sample collection
Sputum is required for this test. A healthcare professional will ask you to collect sputum sample in a clean, dry cup with a lid. There are several ways to collect sputum sample such as:
- Normal coughing: Take a deep breath and exhale. Take another deep breath and cough out sputum into the cup. Do this until the sample has touched the required mark.
- Induced coughing by aerosol saline: Your healthcare professional can also induce coughing by using aerosol saline (salty mist) in case you are unable to collect sample by coughing normally.
- Bronchoscopy: In case, induced coughing does not work, your doctor will perform bronchoscopy to get sputum sample.
- Gastric aspiration can also be retrieved by your doctor in order to get the sputum swallowed by you into the stomach.
After sample collection, the sample is sent to lab for further testing. The sample can be tested for presence of MTB by two methods:
AFB Smear
This is microscopic identification of Mycobacterium infection.
In this test, a smear of the sample is made on a glass slide and it is stained using Ziehl-Neelsen (ZN) stain.
Acid fast bacteria retain the stain even after washing with acid, hence confirming the presence of acid fast bacilli such as Mycobacterium.
This test is quick but it has some drawbacks too.
For example, this test is unable to confirm which species of Mycobacterium is causing infection. Also, further antimicrobial susceptibility testing is not possible in smear. Hence, AFB smear cannot provide definite diagnosis.
AFB Culture
In this test, your sputum sample is subjected to culturing on a suitable culture medium for growth for Mycobacterium. For example, Lowenstein-Jensen media is used for inoculation of sputum sample.
Suitable growth conditions are provided and later these cultures are subjected to biochemical as well as molecular identification methods for species identification.
This test helps in species identification as well as antimicrobial susceptibility testing.
Susceptibility Testing
Antimicrobial susceptibility testing can be done after culturing. This helps in identification of antibiotic which is most effective in clearing mycobacterium infection.
When is Sputum AFB done?
Your doctor will prescribe this test in the following cases:
- If you have chronic cough (more than 3 weeks)
- If you have lung infection
- If you are at high risk of getting TB infection because of recent exposure to infected person
- If you have HIV/AIDS, that puts you at high risk of contracting TB infection due to immune-compromised state
- If you have latent TB infection
- If you have recovered from TB infection, your doctor can use this test to confirm the eradication of bacteria from the body.
Where to get Sputum AFB test done?
The price of Sputum AFB depends on the location and the facility. There are many good options for getting Sputum AFB test in Delhi NCR. The best lab in Delhi NCR for all kinds of diagnostic and imaging is Ganesh Diagnostic and Imaging Centre.
Ganesh Diagnostic and Imaging Centre (GDIC) provide world-class testing facilities at the most reasonable price! Their aim is to provide top-notch technology at an affordable price, without compromising on the quality of service to their patients.
Sputum AFB test available at GDIC:
AFB Mycobacterium Sputum Test at 830 415INR
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Sputum Examination AFB at 420 210INR
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Why Ganesh Diagnostic and Imaging Centre should be your preference?
Ganesh Diagnostic and Imaging Centre is known for providing excellent service and care to its patients for decades. Lakhs of satisfied patients over the years!
It is an established and renowned diagnostic centre since 2001.
Their excellence is backed by NABH and NABL Accreditations.
NABH accreditation is proof of highest standard of care and service provided to the patients. NABL accreditation reflects the competency of laboratories and equipment based on some national and international standards.
The facility for Pathology testing operates 24x7, 365 days, providing service to patients round the clock!
Free home sample collection and digitally available test report enables patients to get tests done at the comfort of their homes.
All safety precautions are taken while collection and transportation of samples. Samples are collected in a hassle-free manner, labeled correctly and transported back to the lab safely.
Test report is generated within 24 hours of sample collection, therefore reducing the gap between diagnosis and treatment effectively.
Test report is available digitally too.
Ganesh Diagnostic and Imaging Centre is a one-stop solution for getting all kinds of tests done, as all services are available under one roof.
The aim of GDIC is to provide world’s finest technology at the lowest price.
The rates of tests are reasonably priced. Ganesh Diagnostic and Imaging Centre also offer FLAT 50% OFF on many tests.
Patients can rely upon test reports as reports are 100% accurate.
Ganesh Diagnostic and Imaging Centre have skilled staff of radiologists, pathologists and technicians.
Ganesh Diagnostic and Imaging Centre is empanelled with various prestigious government and private organizations such as:
- ESIC
- CGHS NHA
- NCDC
- NDMC
- DGEHS
- ECHS
- DELHI JAL BOARD
- DAK
- RAILWAYS
- BSES YAMUNA/ RAJDHANI POWER LTD
- SANJAY GANDHI HOSPITAL
- TATA POWER LTD
- BABA SAHEB AMBEDKAR HOSPITAL
- BJRM HOSPITAL
- ICAR
- BHAGWAN MAHAVIR GOVERNMENT HOSPITAL
- MINISTRY OF HOME AFFAIRS
For more information regarding panels, click here!
Frequently Asked Questions (FAQs) about Sputum AFB test:
What is the purpose of AFB test?
AFB smear test is done for the identification Acid Fast Bacteria such as, Mycobacterium infection. This test is usually done in case tuberculosis infection is suspected.
AFB smear does not provide information about the species of Acid Fast Bacteria responsible for infection.
It is not used as a diagnostic test; rather it is used as an indicative test for the following possible infections:
- TB infection by Mycobacterium tuberculosis
- Non- TB infection by Mycobacterium species
- Tb-like infection in HIV/AIDS patients
What is normal range of AFB?
The smear of AFB is visualized under a microscope after staining. The number of bacilli is counted and reported as +4, +3, +2, and +1. The higher the number of bacilli reported, greater is the infection.
Number of AFB observed Interpretation
(At 1000X magnification)
4+ (>9/field) Strongly Positive
3+ (1-9/field) Strongly Positive
2+ (1-9/10 fields) Moderately Positive
1+ (1-9/100 fields) Moderately Positive
+/- (1-2/ 300 fields) Weakly Positive
No AFB observed Negative
Does AFB positive mean TB?
No, AFB smear positive does not mean the person has TB infection. AFB smear test requires further diagnosis, such as AFB culture and susceptibility testing. These methods help in identification of species of Mycobacterium causing infection.
What if AFB is negative?
AFB negative for smear test does not rule out the possibility of infection, since the person is symptomatic. The reason for false negative can be absence of enough bacteria in the sample for identification. Further diagnosis is required for assurance.
Why 3 sputum samples are collected for TB?
In order to enhance the accuracy of test result, 3 sputum samples are collected. When the test is performed in triplicates, better diagnosis made. The 3 samples are collected on the same day, with a gap of approximately 8 hours between each sample.
How accurate is AFB test?
The sensitivity of Sputum AFB smear for detecting MTB is ranges from 45% to 75%. The accuracy o AFB culture is better than AFB smear for detection. It rarely happens that AFB smear is positive but AFB culture is negative.
