Monday, August 10, 2009

TB or not TB ? Do you have it?

TB goes hand in hand with HIV. That's a fact. Up to 75 % of people diagnosed with TB are also found to be HIV +. A person who is HIV positive lives daily with a 10 fold increased risk in developing TB.

Trying to figure out whether an HIV positive person has TB though, is more difficult and this is where it gets tricky. The healthy immune system responds to any foreign invasion like infections and isolates the invader and destroys it. HIV changes the way the immune system responds to infections, and the more advanced your HIV is, the more dysfunctional your immune system becomes.

What this means, is that it effectively becomes easier for infections and bugs to sneak into your body and take up residence without your immune system realising it. TB is one of these so termed 'opportunistic infections' that pounce on a weakened immune system. So, not only is it more likely for you to become infected with TB, it also becomes more difficult to detect it.

Throughout the world, after decades of studies and experience, we are still battling to figure out exactly what the best way to diagnose TB is. The traditional tests that we rely on, require the isolation of the TB bacteria from tissue or body fluid specimens (like sputum). Once the bacteria is positively identified on sputum for example, the person is termed smear positive or sputum positive for TB.

HIV makes this more difficult, and healthcare workers face the battle of diagnosing TB without a positive specimen - termed smear negative TB. The more advanced the HIV, the greater the chance that all laboratory tests will come back negative for TB. This does not mean that you do not have TB though - all it means is that TB was not found in that particular specimen. You see how TB is a master of disguise?

To diagnose TB in advanced HIV ( a CD4 of less than 200 cells/ul) requires experience, knowledge of TB diagnositc guidelines, a high index of suspicion, and a low threshold to start TB treatment.

What do you need to look out for, you ask? Well, if your CD4 count is less than 200 cells, you are at high risk for TB. If you have the following symptoms TB should be sought out in your body (and this can be absolutely anywhere in the body, not just in the chest):
significant weight loss (a change in dress size/belt size) that may have occurred over many months, night time fevers (hot body), chest pain, abdominal pain, diarrhoea, persistent headache.

You may even have been to your health care provider repeatedly for similar problems, and still not improved. You may have been tested for TB, and told that the tests are negative. You may even have had an Xray. But remember, a health care provider can never tell you that 'you do not have TB'. All they can conclusively say, is that 'we could not find TB in the specimens we looked at', which may mean that you have TB in the body, but it is undetected.

I find certain tests to be extremely useful to assist me to diagnose TB in patients like this: three blood tests - the Full Blood Count, the Erythrocyte Sedimentation Rate, and the C-Reactive Protein. Additionally, I find an abdominal ultrasound and chest xray will often help me to find the circumstancial evidence I need to diagnose TB.

TB can be cured, this we know. But, our current knowledge and expertise still makes it incredibly difficult to diagnose TB. You cannot cure what you have not diagnosed. My message to you: if you are continuously unwell (whether you are on ARV's or not) and are losing weight - ask your doctor to look for TB again, and again. And in some circumstances, starting TB treatment will prove that it was there - because you will get better after starting the medications.

Want to learn more about smear negative Tuberculosis?