3.4.6. Operational aspects of the use of IGRAs

Operational aspects of the use of IGRAs were as follows:

  • Cost of IGRAs was mentioned by four studies, which all stated that the assays are too expensive and that this is a limitation to their use.
  • Only one study addressed reproducibility of T-Spot by assessing inter-observer agreement; it showed excellent correlation. No other study mentioned the issue of test reproducibility
  • Twelve studies reported on accepted transport times of samples to the laboratory, which were mainly less than 6 hours (i.e. within the limit accepted by the test manufacturers). One study accepted a transport time of 16 hours and another 24 hours. None reported on the impact of the transport times (i.e. delay between drawing the blood and initiating the IGRA test) and IGRA test results or performance.
  • No study reported on time-to-result for IGRAs.
  • Four studies reported on the impact of IGRAs on TB therapy. In two studies, IGRA results were reported to clinicians; one study did not discuss the consequences, and in the other study QFT-positive children and adolescents received preventive chemotherapy. The other two studies commented on the reduced number of patients that would require preventive therapy if IGRAs were part of the diagnostic algorithm.
  • The following aspects related to the feasibility of IGRAs were highlighted:
  1. blood amounts required may be an issue; however, tests were performed with less than 2 mL of blood (T-Spot) in some studies; 
  2. a strong interferon response in negative control tubes (high background results) in QFT may reflect the influence of other coincident diseases; 
  3. standardization and generation of automated, quantitative results should render IGRAs more objective than the TST; and
  4. a well-equipped laboratory, expensive equipment and training are required for IGRA test performance, which may cause logistical problems.

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