Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. I have heard that in the United States there is a shortage of tuberculin skin test antigen used for detecting Mycobacterium tuberculosis infection. Is there an alternative that can be used?

A. August 2019—There are two purified protein derivative (PPD) tuberculin antigens—Aplisol (Par Pharmaceuticals) and Tubersol (Sanofi Pasteur)—licensed by the FDA for use in performing tuberculin skin tests (TST). Par Pharmaceuticals had announced that, beginning in June 2019, it anticipated a three- to 10-month shortage of Aplisol. Based on this announcement, the Centers for Disease Control and Prevention recommends the following¹:

• Substitute interferon-gamma release assay (IGRA) blood tests for TSTs. However, clinicians should note that the criteria for IGRA blood test interpretation are different from the criteria for interpreting TSTs. (Interpretation guidelines were published in the CDC’s MMWR Recommendations and Reports in 2010.²) The CDC warns physicians that switching between PPD skin test products or between TSTs and blood tests in serial testing may cause apparent conversions of results from negative to positive or reversions from positive to negative. This may be due to inherent interproduct or intermethod discordance rather than change in M. tuberculosis infection status.
• Substitute Tubersol for Aplisol. Concordance between the two products has been demonstrated in controlled studies.
• “Prioritize allocation of TSTs, in consultation with state and local public health authorities. Prioritization might require the deferment of testing some persons. CDC recommends testing only for persons who are at risk for TB. Groups at high risk for TB infection include 1) persons who are recent contacts exposed to persons with TB disease; 2) those born in or who frequently travel to countries where TB disease is common; 3) those who currently or previously lived in large group settings (such as homeless shelters or correctional facilities); 4) persons with compromised immune systems, including those with health conditions or taking medications that might alter immunity; and 5) children, especially those aged <5 years, if they are in one of the risk groups noted above.”

1. Centers for Disease Control and Prevention. Nationwide shortage of tuberculin skin test antigens: CDC recommendations for patient care and public health practice. MMWR Morb Mortal Wkly Rep. 2019;68(24):552–553.
2. Mazurek GH, Jereb J, Vernon A, et al. Updated guidelines for using interferon gamma release assays to detect Mycobacterium tuberculosis infection—United States, 2010. MMWR Recomm Rep. 2010;59(RR-5):1–25.

Scott J. Zimmerman, DrPH, MPH, HCLD (ABB)
Senior Director
Department of Science and Technology
Laboratory Corporation of America Holdings
Burlington, NC