Oxford, UK; 02 August 2006 – Oxford Immunotec Ltd, the T cell measurement company, has today announced the outcome of two studies comparing its T-SPOT.TB assay with other diagnostic tests for latent tuberculosis (TB) infection. The results of both studies demonstrated that T-SPOT.TB is significantly more sensitive than other diagnostic tests for tuberculosis, far less affected by immunosuppression and is able to provide an accurate result each time a test is carried out.
The first study, published in the Lancet, was conducted in Modena, Italy by Giovanni Ferrara and colleagues. This study compared the performance of the three main assays for detection of TB infection, the traditional Tuberculin Skin Test (TST) and two blood assays, T-SPOT.TB and QuantiFERON®-TB Gold (QFT) (Cellestis: Australia) in routine clinical practice.
The study was conducted in 383 patients enrolled on suspicion of active or latent TB disease. The key findings of the study were that T-SPOT.TB identified more TB positive individuals (38%) than QFT (26%). This difference was statistically significant. In their analysis of the results the authors confirmed their belief that the higher number of positive results identified was explained by the higher sensitivity of T-SPOT.TB.
In a sub-cohort of 24 patients with a diagnosis of active disease, 83% (20 patients) were positive by T-SPOT.TB, 74% were positive by QFT (17 patients) with one indeterminate result and 70% were positive by TST (14 patients).
Indeterminate results were also reported both for the study as a whole and also for a variety of higher risk sub-groups within the study. An indeterminate result occurs when a test is completed but the result cannot be interpreted. This may be caused by a lack of sensitivity in the assay or by the patient having too few T cells to elicit a response. Reported indeterminate rates are given below:
| Group | T-SPOT.TB
Indeterminates |
QFT
Indeterminates |
| Overall result (n=383) |
3% (12) |
11% (43) |
| Patients with cancer (n=40) |
3% (1) |
15% (6) |
| Children under 5 years old (n=22) |
0% |
32% (7) |
| Patients over 80 years old (n=26) |
4% (1) |
12% (3) |
| Patients on systemic corticosteroids (n=34) |
3% (1) |
18% (6) |
| Patients undergoing cancer chemotherapy (n=28) |
21% (6) |
36% (10) |
The findings from the Ferrara study are supported by another study completed at the Asan Medical Centre, Seoul, South Korea by a group led by JY Lee. This study was published in the April edition of the European Respiratory Journal and compared the performance of T-SPOT.TB, TST and QFT in a group of patients with a high clinical suspicion of active TB. The results from this group were compared against a low risk control group of healthy patients.
The overall sensitivity of T-SPOT.TB in the 87 patients diagnosed with active TB disease was 95.4%. This was significantly higher than the results achieved with QFT (70.1%) and TST (66.7%). Moreover 8 patients gave indeterminate results using QFT, while no indeterminates were observed with T-SPOT.TB.
In a sub group of these active TB disease patients (n=29) who also had concomitant immunosuppression, the sensitivity of T-SPOT.TB was unaffected whereas the sensitivity of both QFT and TST fell.
Commenting on the reported findings, Peter Wrighton-Smith, Chief Executive Officer of Oxford Immunotec said, “These studies represent the first significant effort to directly compare the performance of T-SPOT.TB and QFT. It is clear from the results presented in these two papers that T-SPOT.TB is significantly more sensitive than its competitors, far less affected by immunosuppression and is able to provide an accurate result each time a test is carried out with very few indeterminates. We expect the clinical case for T-SPOT.TB to be further strengthened, with a significant number of further studies directly comparing the performance of each of the tests due to be published in the coming months.”
