By Tara Narayan
But will someone tell me why is it so difficult to provide conclusive proof of the tuberculosis bacteria or Mycobacterium tuberculosis within reasonable doubt? Or do we have a case of differential diagnosis all the way merrily till the body is more or less compromised with a slender hope of remission of this complex disease which can move from latent to active depending on …on what?
IT’S absurd or think that tuberculosis is the topmost killer in India yet it is difficult to prove despite a slew of tests – except the expensive ones which can give you proof in two hours if desired! There are two types of tests for TB infection: the TB skin test and the TB blood test. A person’s family doctor or primary health centre should choose which TB test will be fool proof. Factors in selecting which test to use includes the reason for testing, test availability and cost.
Generally, it is recommended to test for TB in a person with both a skin test and blood test but if these are positive it is mostly for the most widely form of TB which is pulmonary and affecting the lungs. Most victims of tuberculosis do not know that there are many kinds of tuberculosis just as there are many kinds of cancer and heart disease. Some kinds of Tb are rare like spinal TB which don’t offer evidence until MRIs are done and ortho and neuro doctors read them conclusively, for TB mimics several other diseases of the interlocked bones, nervous system and muscles system of body beautiful. For example, how do we differentiate spinal TB from pyogenic and fungal vertebral osteomyelitis?
TB TESTS
THE TB skin test is also called Mantoux tuberculin skin test (TST). A TB skin test requires two visits with a healthcare establishment. On the first visit the test is done and on the second visit the test is read and confirmed. At least this is how is done in the US which practically sees nil TB now due to quick standards of detection in hospital labs. New Zealand too is free from TB we learn.
The TB skin test is performed by injecting a small amount of fluid (called tuberculin) into the skin on the lower part of the arm. A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm. The result depends on the size of the raised, hard area or swelling. This means the person’s body was infected with TB bacteria. Additional tests are needed to determine if the person has latent TB infection or TB disease. Negative skin test means the person’s body did not react to the test, and that latent TB infection or TB disease is not likely.
There may be repeat tests in a different location of the body, for example the other arm. This is the preferred testing for children under age of five — the TB skin test (TST) and TB blood test. A positive TB skin test or TB blood test only tells that a person has been infected with TB bacteria. It does not tell whether the person has latent TB infection (LTBI) or has progressed to TB disease.
TB BACTERIA IN BODY
THE tuberculosis blood test, also called an Interferon Gamma Release Assay or IGRA, is a way to find out if you have TB bacteria in your body. The TB blood test can be done instead of a TB skin test (Mantoux). There are two kinds of TB blood tests: QuantiFeron TB (09 Nov 2022)
TB has been around in the world ever since the dawn of civilisation and as part of the human experience. It’s an ancient scourge of a disease which doesn’t get the attention it deserves despite all the hype and hoopla of big funded programs. Archaeologists have found TB in the remains of a mother and child buried together. The earliest written texts of India mention the prevalence of TB (3,300 years ago) and China (2,300 years ago). Throughout the 1600s-1800s in Europe TB caused 25% of all deaths (as per 2023 studies) and hence the charitable building of sanitoriums where the emphasis was on fresh air, fresh sunlight and fresh fruit and food.
However, the more we read up medical research the more we learn that no diagnostic test is ever completely fool proof. If thousands and thousands of people are tested, mistakes happen. A good diagnostic test is one with a high sensitivity (detects people with TB) and also a high specificity (correctly identified healthy people without TB). Sensitivity and specificity are expressed in percentages. Good tests should have a sensitivity and a specificity at least above 90%.
For example, a TB diagnostic with a sensitivity of 95% and a specificity of 99% would correctly identify one out 100 people who do not have TB! Difficult to swallow? The first step to detecting TB infection, after taking a medical history and doing a physical exam, is to do a chest X-ray.This allows the health worker to examine the lungs of the person suspected with TB infection. On a chest X-ray from someone with TB you can often see the cavitation that the TB bacteria forms in the lung tissue. Chest x-rays are usually poor specificity. The diagnosis of TB cannot be made by a chest X-ray alone. It can also not be excluded by a chest X-ray.
LATENT TB MYSTERY
A PERSON with latent, or inactive, TB will have no symptoms. You may still have a TB infection, but the bacteria in your body is not yet causing harm. Symptoms of active TB include: A cough that lasts more than three weeks. Loss of appetite and unintentional weight loss. Fever. Chills. Night sweats. Coughing up blood or mucus (sputum) is a sign of pulmonary TB and is infectious enough for precautions to be taken by the arrest of the family.
Bone pain may mean that the bacteria have invaded your bones. These symptoms can also occur with other diseases, so it is important to see a doctor who is educated about TB. If you think you have been exposed to TB (a lot of our domestic workers may be latent TB patients who do not suffer but can pass the disease on to you). Get a TB test but that is easier said than done given the half-a-dozen common and rare forms of TB which manifest in the body.
Collect history, physical exam, use stethoscope to listen to your lungs and check the lymph nodes in your neck for swelling. If doctor suspects TB order skin or blood test. The skin test is done by injecting a small amount of fluid called tuberculin into the skin of the arm. You will be told to return to the office within 48 to 72 hours to have a healthcare worker check the arm to see if a bump or an induration (thickening) of the skin has developed. It may be difficult to feel so an experienced TB medical staff should examine the reaction. The bump tells you if your reaction to the test is positive or negative. If it’s positive, it usually means you have been infected with the TB germ. It does not tell whether you have developed clinically active TB disease.
The skin test isn’t 100% accurate, meaning you may have a false-positive or a false-negative, so your doctor may order further testing regardless of the result. The TB blood test measures how your immune system reacts to the germs that cause TB. This information will be used to more precisely confirm or rule out latent or active TB. It requires only one visit to a good medical facility. If the skin or blood tests indicate the need for further analysis, a chest X-ray or CT scan is prescribed for visible signs of TB in your lungs.
They may also check your sputum (coughed up mucus) to bacteria, to see whether you have clinically active TB disease and if so, which strain of TB you have. These tests can take one to two months before results are available.
We are also hearing of the Rapid Tuberculosis Test from a US national research authority. Diagnosis of active tuberculosis means finding the bacterium in a sample of bodily fluid from the patient. Where the bacterium is found depends on where the infection takes place in most cases. Mycobacterium tuberculosis infects the lungs (see Pulmonary Tuberculosis). If that is the case, the bacterium can be found in sputum. Sputum is a very thick bodily fluid (also called mucus) which comes from the lower airways. It is thicker than saliva and is usually coughed up.
There are two ways to test sputum for Mycobacterium tuberculosis: with a sputum smear and with a sputum culture. In both tests, the aim is to find Mycobacterium tuberculosis through colouring it in the sputum.
NEW TESTS
RECENTLY, a new test has been developed to diagnose active TB. It is called the GeneXpert, and also uses sputum samples. If the sample contains TB bacterium, it multiplies its DNA (the “genes” of the bacterium, DNA is short for desoxyrubinucleic acid) through a method called PCR (polymerase chain reaction). This allows it to detect TB bacterium very reliably and also very fast – it only takes about two hours for the test to come to a result. So far, it has had good sensitivity and specificity and it can also test if the TB bacterium is resistant to one of the TB drugs rifampicin. However, the GeneXpert machine is not widely available yet.
Over and over again we hear that no diagnostic test is ever completely fool proof! Indeed, TB is a very complex disease and may oftentimes be misdiagnosed and a patient treated wrongly with medicines which will take a toll in the form of side effects in kidneys and liver. You may be gone with the wind because of some other disease altogether never detected!
But not joking: How widely are the new tests for TB available in Indian medical facilities and in Goa? Tests like the aforementioned test and including the NAATs or nucleic acid amplification test which represents a substantial advancement in the diagnosis of TB. This has been available in the US for the last two decades offering better accuracy than AFB microscopy and greater speed than culture tests. NAATs is now standard practice in US to detect and confirm TB anywhere in the body. In India we need to take the disease of TB more seriously than we do perhaps!