Influence of pre-analytic conditions on the rate of indeterminate T-SPOT®.TB tests

To the Editors: A prior study has demonstrated that the rate of indeterminate T-SPOT®. TB (Oxford Immunotec, Abingdon, UK) test results performed under routine field conditions was low (3.4%) [1]. Indeterminate test results were more common in individuals aged >75 yrs and may be influenced by the transport conditions (cold weather in winter). Since this study was published, two technical improvements in the pre-analytic conditions were introduced. The first is the use of lithium heparinate blood sample collection tubes instead of the CPT™ Cell Preparation Tubes with sodium citrate (Vacutainer®; BD, Franklin Lakes, NJ, USA), as used in the prior study; the other is the use of the T-Cell Xtend ™ reagent (Oxford Immunotec) in samples >8 h old [2]. The Meditest reference laboratory (Lausanne, Switzerland) receives blood samples from remote places in Switzerland, so that many samples travel overnight or for ≤36 h before being analysed. All samples that have been collected >8 h earlier are processed with T-Cell Xtend . We therefore performed an updated analysis of the data from the beginning of 2010 to compare the rate of indeterminate tests …