TB in Primary Care: New Diagnosis and Treatment Guidelines

Neil Skolnik, MD


November 25, 2020

This transcript has been edited for clarity.

I'm Dr Neil Skolnik, professor of family and community medicine at the Sidney Kimmel Medical College at Thomas Jefferson University.

Today we are going to talk about guidelines for the diagnosis and treatment of latent tuberculosis (TB) which have changed dramatically recently. Under the old guidelines, published almost 20 years ago, we'd do a purified protein derivative (PPD). If it was positive, we would treat with 9 months of isoniazid (INH).

That's all now changed with the publication of diagnosis guidelines from the Infectious Diseases Society of America and now this year, the updated treatment recommendations from the Centers for Disease Control and Prevention.

Let's start with the diagnosis guidelines.

The primary test in most circumstances is the interferon-gamma release assay (IGRA), more commonly known as the QuantiFERON-TB Gold test. That test is now recommended over the PPD because it is more specific, meaning there are fewer false positives.

We can think about diagnosis in three buckets.

The first is people who are at very low risk, who don't need to be tested unless required by work or school. These people have a very low pretest probability of disease. They should get a QuantiFERON test. If you choose to give them a PPD, it is only considered positive if the diameter of the reaction is greater than 15 mm. If either the QuantiFERON or the PPD is positive — and this is a really important change — a second test should be done before saying that the patient has latent TB. And only if the second test is positive should the patient be diagnosed with latent TB and go on to treatment.

In the second bucket are people at low to medium risk. QuantiFERON is the recommended test. If a PPD is done, a positive reading is one greater than 10 mm. If either test is positive, the diagnosis is confirmed.

In the third bucket are high-risk individuals. Either a QuantiFERON or a PPD can be used. Consider using both tests if the person is at very high risk (eg, having had a recent exposure). The PPD is considered positive if it is greater than 5 mm. Since the patient is at high risk, the diagnosis is confirmed if either of the two tests is positive.

Let's go on to treatment of latent TB. Remember, before treating for latent TB, make sure that the patient does not have active TB. Ask about symptoms and get a chest x-ray.

Treatment used to be 9 months of daily INH. That has changed. Based on efficacy (which is the same with the new regimens), ease (the new regimens are much shorter in duration so there is a greater chance of patients complying and competing the regimens), and safety (less hepatic toxicity), rifamycin-based regimens are recommended. This makes it easier for us and for patients. The regimen is 4 months of daily rifampin or 3 months of daily INH plus rifampin.

If directly observed therapy is needed, or you or the patient prefers weekly treatment, then 3 months of once-weekly INH plus rifapentine can be given. INH is now an alternative regimen, given daily either for 6 or 9 months.

I'm Neil Skolnik, and this is Medscape.

Neil Skolnik, MD, is professor of family and community medicine at the Sidney Kimmel Medical College of Thomas Jefferson University, and associate director of the Family Medicine Residency Program at Abington Jefferson Health. He has published over 350 articles, essays, poems, and op-eds in the medical and nonmedical literature as well as four medical textbooks and a book of short stories. He also hosts the American Diabetes Association's monthly Diabetes Core Update podcast. Follow him on Twitter: @NeilSkolnik

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