Questions on PPD testing

[lordman]

What is the next step (CXR, repeat TST after 8 weeks, or start treatment) in this scenario:

- A health care worker with negative TST, then had a recent contact with a TB patient. 7 mm induration on the second TST testing.

Really confusing scenarios. I am confused if we count the health worker as a close contact (so positive PPD (> 5 mm); next step is CXR to exclude active TB) VERSUS if we still consider health worker as health worker regardless to his contact with a TB patient (so negative PPD < 10 mm), next step is repeat TST after 8 weeks). Any thoughts?

---

Members don't see this ad.

 

[Phloston]

Quoting UpToDate:

"Close contacts of patients with active pulmonary tuberculosis – These individuals may have an initial negative TST because the tuberculosis (TB) infection was so recent that delayed hypersensitivity has not yet developed. In these individuals, the TST should be repeated eight weeks after the last exposure, since it takes three to seven weeks for tuberculin conversion to occur after new infection [15]. The same technique and dose is used, but the test is applied on the opposite forearm."

So the answer is repeat in 8 weeks.

Even though >5 mm is considered (+) in someone with recent exposure to a person with known active TB, healthcare workers must have >5 mm ABOVE BASELINE for the test to be considered positive after recent exposure (or >10 mm above baseline in absence of known exposure). So for this healthcare worker in your vignette, her baseline is 7 mm because you know she can't possibly have a genuinely (+) PPD this early. So you repeat the test in eight weeks' time. If she has > 12 mm, she's considered (+). If she is <12 mm, she's negative.

HOWEVER, if the partner, for instance, of this same patient had 6 mm induration and negative CXR, the answer for him would simply be 9 months of INH as prophylaxis. That's because we don't know his baseline so we just have to assume he's positive. His baseline could actually be zero mm for all we know, which is the case for some people.

UpToDate mentions that the PPD sensitivity is 98% when 5 mm is set as the cut-off, 90% with 10 mm, and 50-60% with 15 mm, RELATIVE TO THE BASELINE. In the community, we just assume everyone's baseline is zero. In healthcare workers, we have it on record every year.

http://www.uptodate.com/contents/di...tuberculosis-screening-in-hiv-negative-adults

http://www.uptodate.com/contents/tuberculin-skin-test-drug-information?source=see_link

Hope that helps,

 

[lordman]

Thanks phloston. But the healthcare worker had 7 mm on the second TST, not the first one. The first one stated as negative.
What do you think?

 

[Phloston]

Still have to wait 8 weeks.