Background New more sensitive and specific immunologic tests – Interferon γ Release Assays (IGRA) – for diagnosis of latent tuberculosis infection (LTBI) have been developed, but their higher cost needs to conduct cost-effectiveness (CE) assessment to determine how they can be implemented in the diagnostic strategy.
Objectives To evaluate the CE of different IGRA-based LTBI diagnostic strategies comparatively to tuberculin skin test (TST) in patients before starting anti-TNF therapy.
Methods 429 patients with rheumathoid arthritis, spondylarthropaty or Crohn’s Disease with an indication for initial biological treatment with anti TNF therapy were included in the ETAT study1. All patients were tested by TST and 2 different IGRA: QUANTIferon TB Gold in tube (QTF-Gold IT) and T-SPOT.TB. A decision tree was used to represent the different strategies: (a) TST alone (reference) and 5 alternative strategies(see table). The model was filled with probability values from ETAT study and direct medical costs (TST, IGRA and LTBI treatment including monitoring in case of positive LTBI detection; in euros (€)) from the French health care payers’ perspective. The effectiveness was measured in terms of percentage of patients without LTBI treatment. The incremental cost effectiveness ratio (ICER) was expressed in terms of cost in € per LTBI treatment avoided. Construction of decision tree and analysis was performed using TreeAge Pro 2012.
Results Data were available for 392 patients and none of them developed a TB. The effectiveness of the different strategies was: 65% (a), 82% (b, c, e), 81% (d), and 89% (f). The cost of the strategies was: 172€ (a), 329€ (b), 345€ (c), 345€ (d), 277€ (e) and 146€ (f). Results are shown in the table. The dominant strategy was (f) and the ICER was assessed at -104€ by LTBI treatment avoided. For the other strategies the ICER were assessed: 924 (b), 1020 (c), 999 (d), 530 (e).
Conclusions According to the good specificity of QTF Gold IT and TSPOT.TB, the absence of a real gold standard for the LTBI diagnosis and the absence of active TB under Anti-TNF during this study, using the percentage of patient without preventive TB treatment for the effectiveness must be considered as a good option. In this case the dominant strategy was based on QTF Gold ITalone or with TSTwhen the result of QTF Gold ITwas indeterminated.
Mariette X et al., Influence of replacing TST with ex vivo IGRA on decision to administer prophylactic antituberculosis antibiotics before anti-TNF therapy. Ann Rheum Dis. 2012 Nov;71(11):1783-90.
Disclosure of Interest None Declared