Tuesday, July 05, 2005

Decision to test is a decision to treat?

This is a short case concerning a young man referred to my clinic after undergoing his pre-University physical/health screen.

18 year old young man presented to his PCP about one month prior to his first semester of college. His history was unremarkable and no abnormalities were found on exam. The young man's mother asked the physician to place a PPD.

Three days later his PPD was read as indurated at 55 mm. A PA/LAT was normal.

He was in our clinic about one week into his studies. Again, completely unremarkable history and exam. No TB risk factors. CXR negative.

How would you proceed ?

10 comments - CLICK HERE to read & add your own!:

Jennings said...

Was it confirmed that it was 55 mm induration and not just redness? Did a qualified reader read the test? I assume there is no history of TB exposure. He wasn't volunteering in a homeless shelter before college, etc.
Blue journal recent article about using interferon gamma blood test in those without any identifiable RF's and found that the test would be usful for identifying latent TB in those with the BCG vaccine.

I'm not sure how to apply that test to this patient, but it may be worth it. In the end, it might make sense just to treat him for latent TB.

Mendez said...

Yes.. confirmed. We called the clinic the same day. We assumed the same thing, a likely misread. However, we confirmed the finding; several people confirmed the size as they don't often see 55 mm induration.
No risk factors/TB exposures. No BCG.

Baleeiro said...

At that level of induration the BCG would not be very relevant anyway. One could make the argument that this is latent TB, he has now a lifetime 10% risk of getting active TB and at his age the risks of any significant adverse reaction to INH Tx would be way less than 1%. I would present those options and stats and help him make an informed consent. I have recently seen a very similar case (healthy 19 y/o woman, no TOB, no HIV, etc.) but her case was made a little easier: her initial employment PPD was negative and 2 years later it is now positive. Since she was a recent converter she chose to take INH.

Mendez said...

Good comments. In fact, we presented him with the options you suggested (with associated risk), and chose to treat him.

Of course, a case like this illustrates the limitation of guidelines. The PCP for this patient may or may have not known the guidelines, but a patient like this was clearly not in an at-risk population.

So, now, given a result of 55 mm induration, we assumed that this was not likely a false-positive result.

We treated him with INH for 9 months. However, I was concerned when he asked about how much he could drink (remember frehsman in college). Also, compliance was less than optimal a couple of times throughout the treatment period.

In retrospect, would you still have treated him?

Baleeiro said...

I think Mendez makes a great point about ordering tests. The patient's PPD was positive so the guideline not testing him might have failed him... I probably would NOT have checked his PPD (so I would have missed it as well) but since it was done I would treat him.
To me it is similar to CT screening for lung cancer: I would not go around doing screening CTs on every Pt until all the trials are done but if someone else gets a CT and comes to see me I will investigate the abnormalities.

Baleeiro said...

There are now blood tests for LTBI in TB contacts (AJRCCM 2004; 170: 65) with good discrimination compared to PPDs. I don't think it is worthwhile checking into it for this otherwise young and healthy patient. However, if he was very unsure and searching for a "tie-breaker" or in more complicated situations this might prove useful.

Jennings said...

I think that was the blue journal article i alluded to eh? Wasnt that ifn-gamma (serum test)?

Jeff H said...

I believe there are a couple of ELISA-based blood tests comercially available now. They hav MTb antigen captured on the dish that is incubated with whole blood. The T-cells that recognize the MTb antigen release the Interferon, which is then measured.

The nice thing about these tests is increased specificity; the antigens used are not present on atypical mycobacteria. There have been two papers recently- I believe the one in the blue journal was used to test following a known exposure in a ??Dutch?? school. It was compared to PPD, and did quite well, with similar/better sensitivity and better specificity.

The other study, I think, looked at the serum test in context of people with prior BCG. Again, it did a better job discriminating than the PPD.

I don't think there are any studies yet looking at these blood test in terms of "screening." It is also not yet known if it looses sensitivity with time after exposure.

Baleeiro said...

Jeff H is correct: the blue Journal ref I added is of post-exposure conversion (in a Danish school) and even stratified for what they considered "high" exposure (same classroom, etc.) and "low" exposure (same school but no direct contact).
Since it is a relatively new set of tests the uses will probably have to evolve. My point was not to use it for everybody but to raise awareness of its availability given its good specificity.

Jeff H said...

Absolutely--that is my point as well. I don't think it should be used for everybody, as it has not been studied that way. It's role is developing. For now, I'd use it as discussed--for difficult decisions, questions regarding cross-reactivity of the PPD in low-exposure risk patients (or, possibly, for patients at high risk for treatment of LTBI...)