It would appear that following a +TST with a QFT is more expensive than QFT alone.
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The objective of the (first) study was to look at the cost-effectiveness of the QFT (QuantiFERON®-TB Gold) compared with the TST for TB contact screening in Japan. The target population was 20-year-old close contacts of patients with sputum smear-positive TB, and the main outcome measure was the incremental cost per quality adjusted life year (QALY) gained during the lifetime with an annual discount rate of 3%.
They looked at three strategies for screening the contacts:
1) TST alone;
2) TST followed by QFT; and
3) QFT alone.
They calculated the probability of having TB at a value of 0.2. They calculated the sensitivity of QFT testing at 0.76 and the specificity at 0.96, while the sensitivity for the TST was 0.71 and the specificity was 0.36.
The cost of doing one TST was calculated at $7.40 (range $5–12) and the cost of the QFT diagnostic kit was $34.2 (range $20–50). They calculated the cost of 6 months of INH at $433.30; treatment of any INH-induced hepatitis at $10,000; TB treatment for 6 months at $12,500; and treatment for MDR-TB at $125,000.
Based on these cost figures and test results, they calculated the overall costs of
the QFT-alone strategy at $471.54;
the TST and QFT strategy at $500.55 (+$29.01); and
the TST-alone strategy at $573.98 (+$102.44).
..Their conclusions for Study 1 are:
1) the QFT-alone strategy is most cost-effective for TB contact screening in Japan;
2) when the TST specificity is over 0.72, the TST followed by the QFT strategy is more cost effective than the QFT-alone strategy, at a level of US$25,000/QALY gained as willingness to pay; and
3) the QFT-alone strategy would be more cost-effective in individuals at high risk of TB mortality, such as the elderly.
The objective of the second study involved determining the cost-effectiveness of the QFT compared with the TST for annual TB screening of HCWs in Japan. The target population was 20-year-old HCWs and the main outcome measure was the incremental cost per QALY gained during a lifetime with an annual discount rate of 3%. The three strategies looked at for annual HCW screening for TB were:
1) a twostep TST followed by a chest X-ray;
2) QFT followed by a chest X-ray; and
3) a QFT alone strategy
..For this study they calculated the cost of one TST at $9.30; the cost of a QFT diagnostic kit at $43.20; the cost of chemoprophylaxis for 6 months at $546.80; the treatment of INH-induced hepatitis at $12,620; the cost of TB treatment for 6 months at $15,775; and the very important cost of contact screening at $4,000. Looking at the incremental cost effectiveness of the three strategies, they calculated that
the QFT-alone strategy cost $3408.13;
the QFT/chest X-ray strategy $3450.04; and
the 2-step TST/ chest X-ray strategy $3846.96.
..Their conclusions were that:
1) the QFT-alone strategy is the most cost-effective in BCGvaccinated HCWs in Japan; and
2) when the probability of having LTBI is over 0.463, the QFT/chest X-ray strategy may be more cost-effective than the QFT-alone strategy, at a threshold of US$25,000/ QALY as a willingness to pay
DISCUSSION
Q: What was the time horizon for your first study?
A: This was a lifetime study for the study population.
Q: One conclusion was that the probability of having LTBI was 46%. That would probably never happen?
A: That is the model and this presentation is only reporting the results of that model.
Q: How much does an X-ray cost in Japan? Our strategy in the US is to TST and maybe in the future do the QFT first and then X-ray the positives and then do INH for converters. Do you repeat the X-ray annually for life?
A: The X-ray cost is about 36 dollars. In our study we chose to put the Japanese guidelines into the model and the guidelines require the chest X-ray to be repeated annually.
