Sputum for AFB Test
If you have been asked to give a sputum sample for an AFB test, you are likely being checked for tuberculosis (TB). AFB stands for acid-fast bacilli, a group of bacteria that includes Mycobacterium tuberculosis — the main cause of pulmonary TB. The test is a simple, low-cost microscopic examination of your sputum (phlegm coughed up from the lungs) and is the first-line diagnostic tool for TB in Bangladesh, especially under the National Tuberculosis Control Programme (NTP). While the test is valuable, it has limitations: it can miss some cases and cannot distinguish TB from other acid-fast bacteria. A doctor must interpret the result together with your symptoms and other tests.
What Is the Sputum AFB Test?
The sputum AFB test (also called sputum smear microscopy) involves staining a sample of your sputum with a special dye, then examining it under a microscope for red, rod-shaped bacteria. The term “acid-fast” refers to the bacteria’s waxy cell wall that resists decolorization by acid-alcohol — a property that makes them stand out under the microscope. This test is widely used in Bangladesh because it is inexpensive, requires minimal equipment, and can provide results within 24 hours. However, it is less sensitive than culture or molecular tests like GeneXpert. Culture can grow the bacteria and confirm TB, while GeneXpert detects bacterial DNA and also checks for drug resistance. For most patients, the AFB smear is the starting point.
Why Sputum Instead of Blood or Urine?
TB bacteria primarily infect the lungs and multiply in the airways. When you cough, the bacteria are expelled in the mucus (sputum). Collecting sputum directly from the lungs gives the highest chance of finding the bacteria. Blood tests, such as the Mantoux skin test or interferon-gamma release assays (IGRAs), only show whether your immune system has encountered TB bacteria — they cannot confirm an active lung infection. Urine tests are not used for pulmonary TB. Some people worry that coughing up sputum is painful or dangerous, but it is a routine, safe procedure. A healthcare worker will guide you to produce a good sample.
Who Should Take This Test? (Common Symptoms)
A doctor typically orders the sputum AFB test if you have any of the following symptoms, especially lasting more than two weeks:
- A persistent cough that does not improve
- Coughing up blood or blood-stained sputum (hemoptysis)
- Night sweats
- Unexplained weight loss
- Fever, especially low-grade that comes and goes
- Chest pain or shortness of breath
The test is also used for contact tracing — if you live with someone diagnosed with TB — and for screening high-risk groups such as people with HIV, diabetes, or those who work in crowded settings like prisons or factories.
How to Collect Sputum the Right Way
Getting a good sputum sample is essential for accurate results. Saliva or mucus from the nose is not acceptable. Follow these steps:
| Key Point | Detail |
|---|---|
| Best time | Early morning, before eating, drinking, or brushing teeth — bacteria are most concentrated overnight. |
| Technique | Take a deep breath, hold it for a few seconds, then cough forcefully from deep in your chest. Spit the phlegm into a sterile, wide-mouthed container. |
| Amount needed | About 3–5 mL (a teaspoonful) of thick sputum, not saliva. |
| Number of samples | Usually three samples on separate days (spot-morning-spot or two morning samples). |
| Storage | Keep the container cool (refrigerate if delay >1 hour) and deliver to the lab within 2 hours if possible. |
| Avoid | Do not use mouthwash, eat, or brush teeth before collection — these can kill bacteria or contaminate the sample. |
If you have difficulty coughing up sputum, a healthcare worker may use a nebulizer (steam inhalation) to help loosen it.
What Do the Results Mean?
The laboratory reports the result as negative (no AFB seen) or positive with a grade indicating the number of bacteria per microscopic field:
| Result | Meaning |
|---|---|
| Negative | No acid-fast bacilli seen in 100 fields. Does not rule out TB — especially in children, HIV patients, or those with early disease. |
| Scanty | 1–9 AFB per 100 fields. Suspicious; repeat or do a molecular test. |
| 1+ | 10–99 AFB per 100 fields. Positive — TB is likely. |
| 2+ | 1–10 AFB per field in at least 50 fields. Strongly positive. |
| 3+ | More than 10 AFB per field. Very high bacterial load. |
Smear microscopy detects about 60–70% of TB cases in ideal conditions, while culture and GeneXpert have higher sensitivity (over 90%). A negative smear does not exclude TB, and a positive smear does not confirm it is M. tuberculosis — other acid-fast bacteria (non-tuberculous mycobacteria) can also appear. Your doctor will consider your chest X-ray, symptoms, and possibly a GeneXpert or culture test before starting treatment.
Sputum AFB Test Cost in Bangladesh
In Bangladesh, the sputum AFB test is available free of charge at government hospitals and NTP-designated diagnostic centres. Private laboratories charge a fee that varies by city, lab quality, and whether a package for three samples is offered. The table below gives approximate ranges — always confirm the current price before testing.
| Item | Approx. BDT Range | Notes |
|---|---|---|
| Single AFB smear (private lab) | 200 – 600 ৳ | Per sample; price may be lower in smaller cities. |
| Three-sample series (private lab) | 500 – 1,500 ৳ | Some labs offer a discounted package for the full set. |
| GeneXpert (private lab) | 1,500 – 3,000 ৳ | Often done if smear is negative but TB is still suspected. |
| Public hospital / NTP | Free | Available at all government TB clinics and many district hospitals. |
Prices change over time and vary by facility. Call the lab beforehand to ask about current charges and whether they accept samples from outside patients.
What Happens After a Positive or Negative Result?
If the result is positive: Your doctor will likely start you on standard TB treatment (a combination of antibiotics for 6 months). You may also need a GeneXpert test to check for rifampicin resistance. Treatment is free under the NTP. It is important to complete the full course and not stop early.
If the result is negative but symptoms persist: Your doctor may order a chest X-ray, a repeat sputum AFB test, or a GeneXpert test. TB can be present even when the smear is negative — this is called smear-negative TB. Children, people with HIV, and those with early disease often have low bacterial loads. Never start or stop TB medication on your own; only a qualified physician can decide the right treatment based on all available information.
Find Pulmonologist Doctors by Division in Bangladesh
If you need expert care for TB or other lung conditions, you can search for pulmonologists in your division using the links below.
| Division | Find a Doctor |
|---|---|
| Dhaka / ঢাকা | Popular Pulmonologist Doctors in Dhaka |
| Chattogram / চট্টগ্রাম | Top Pulmonologist Doctors in Chattogram |
| Khulna / খুলনা | Find Pulmonologist Doctors in Khulna |
| Rajshahi / রাজশাহী | Rajshahi Pulmonologist Doctors |
| Rangpur / রংপুর | Pulmonologists in Rangpur |
| Sylhet / সিলেট | Pulmonologists in Sylhet |
| Barishal / বরিশাল | Top Pulmonologist Doctors in Barishal |
| Mymensingh / ময়মনসিংহ | Popular Pulmonologist Doctors in Mymensingh |
Frequently Asked Questions
How many sputum samples are required for the AFB test?
In Bangladesh, the standard practice under the National Tuberculosis Control Programme is to collect two sputum samples: one at the first visit (spot sample) and another the next morning (early morning sample). Some clinics may request a third sample if the first two are unclear. Always follow the exact instructions given by your healthcare provider.
Is there any special preparation needed before collecting sputum?
No special diet or fasting is required. However, it is best to rinse your mouth with plain water before coughing to avoid food particles or toothpaste residue mixing with the sample. Do not use mouthwash or gargle with antiseptic, as it may kill the bacteria and affect the test result.
What should I do if I cannot produce sputum?
If you have difficulty coughing up sputum, try taking a few deep breaths, then cough forcefully from deep in your chest. Drinking warm water or inhaling steam for 10–15 minutes may help loosen the mucus. If you still cannot produce sputum, inform your doctor or the laboratory staff. They may use a nebuliser with saline to induce sputum or consider alternative tests.
How long does it take to get the AFB test results?
The microscopic examination of sputum for AFB usually takes 24 to 48 hours. In many government facilities under the NTP, results are available within the same day or the next working day. However, if a culture or molecular test (like GeneXpert) is also needed, results may take several days to weeks. Your doctor will tell you when to expect the report.
Can the AFB test tell if the TB bacteria are drug-resistant?
No, the standard AFB smear microscopy cannot determine drug resistance. It only shows whether acid-fast bacilli are present. If the smear is positive, your doctor may order additional tests such as GeneXpert or culture and drug susceptibility testing (DST) to check for resistance. These tests are available at designated TB centres in Bangladesh.
Sources
The following sources are from international journals, government health agencies, or recognized medical organizations:
- WHO guidelines on TB diagnosis (who.int)
- NHS – Sputum Test for Tuberculosis (nhs.uk)
- Mayo Clinic – Tuberculosis Diagnosis (mayoclinic.org)
- DGHS Bangladesh – National Tuberculosis Control Programme (dghs.gov.bd)
- World Health Organization — Sputum for AFB Test (who.int)
- MedlinePlus — Sputum for AFB Test (medlineplus.gov)