Tuberculosis Test Usage and Medical Expenditures from Outpatient Insurance Claims Data, 2013

Skin tests for the detection of Mycobacterial infections: achievements, current perspectives, and implications for other diseases

Immunological and molecular advances have modernized diagnostic testing for many diseases. Although interferon gamma-release and polymerase chain reaction assays have been developed to detect Mycobacterium tuberculosis (Mtb) infection, purified protein derivative (PPD)-based tuberculin skin testing (TST) remains the most widely used method. Indeed, the TST is a simple and cost-effective tool that can be easily applied for widespread screening for Mtb infection. However, the lack of specificity has been a limitation of these tests, and, more recently, supply issues have arisen. Building upon the skin tests that historically have been used within TB and leprosy control programs, we discuss recent developments using modern technologies for improving mycobacterial skin testing as well as practical advantages inherent to the technique. Furthermore, we outline how this knowledge could be applied to develop similar tests that could benefit diagnostic strategies for other infections. KEY POINTS: • Skin testing provides a significantly cheaper alternative to most modern technologies. • Skin tests provide a lab-independent diagnostic strategy that can be widely administered. • Diseases for which T cell responses are more robust or durable than antibody responses are accessible for skin testing.

The single recombinant M. tuberculosis protein DPPD provides enhanced performance of skin testing among HIV-infected tuberculosis patients

Diagnostic testing for M. tuberculosis infection has advanced with QuantiFERON and GeneXpert, but simple cost-effective alternatives for widespread TB screening has remained elusive and purified protein derivative (PPD)-based tuberculin skin testing (TST) remains the most widely used method. PPD-based tests have reduced performance, however, in BCG vaccinees and in individuals with immune deficiencies. We compared the performance of skin testing with the recombinant DPPD protein against that of a standard PPD-based skin test. Our data indicates similar performance of DPPD and PPD (r² = 0.7689) among HIV-negative, active TB patients, all of whom presented greater than 10 mm induration following administration. In contrast to results demonstrating that PPD induced indurations greater than 5 mm (i.e., the recommended threshold for positive results in this population) in only half (19 of 38) of the HIV positive TB patients, 89.5% (34 of 38) of these participants developed indurations greater than 5 mm when challenged with DPPD. Importantly, none of the patients that were positive following PPD administration were negative following DPPD administration, indicating markedly improved sensitivity of DPPD among HIV-infected individuals. Our data indicate that DPPD has superior performance in skin testing than the current TST standard.

Estimates of Testing for Latent Tuberculosis Infection and Cost, United States, 2013

OBJECTIVES

Tracking trends in the testing of latent tuberculosis infection (LTBI) can help measure tuberculosis elimination efforts in the United States. The objectives of this study were to estimate (1) the annual number of persons tested for LTBI and the number of LTBI tests conducted, by type of test and by public, private, and military sectors, and (2) the cost of LTBI testing in the United States.

METHODS

We searched the biomedical literature for published data on private-sector and military LTBI testing in 2013, and we used back-calculation to estimate public-sector LTBI testing. To estimate costs, we applied Medicare-allowable reimbursements in 2013 by test type.

RESULTS

We estimated an average (low-high) 13.3 million (11.3-15.4 million) persons tested for LTBI and 15.3 million (12.9-17.7 million) LTBI tests, of which 13.2 million (11.1-15.3 million) were tuberculin skin tests and 2.1 million (1.8-2.4 million) were interferon-γ release assays (IGRAs). Eighty percent of persons tested were in the public sector, 18% were in the private sector, and 2% were in the military. Costs of LTBI tests and of chest radiography totaled $314 million (range, $256 million to $403 million).

CONCLUSIONS

To achieve tuberculosis elimination, millions more persons will need to be tested in all sectors. By targeting testing to only those at high risk of tuberculosis and by using more specific IGRA tests, the incidence of tuberculosis in the United States can be reduced and resources can be more efficiently used.