evaluation of latent tuberculosis infection in patients with inflammatory arthropathies before treatment with tnfalpha blocking drugs using a novel flowcytometric interferongamma release assay objective to compare the efficacy of the conventional skin test and a novel flow cytometric whole blood assay in the diagnosis of latent tuberculosis infection ltbi in patients with rheumatological diseases evaluated for treatment with tnfalphablocking agentsmethods prospective study of 97 consecutively enrolled patients who were assessed for the presence of ltbi through clinical history mendelmantoux skin testing and chest xray in addition tcell reactivity towards tuberculin ppd purified protein derivative and the mycobacterium tuberculosisspecific proteins esat6 and cfp10 was determined ex vivo using a flow cytometric whole blood assayresults after standard screening 15 of patients receiving tnfalphablocking therapy were pretreated with isoniazide inh another 5 of patients did not receive tnfalphablocking therapy because of ltbi ppdreactivity in the skin was observed in 14 of patients compared with 39 with the whole blood test analysis of the m tuberculosisspecific response to esat6 and cfp10 revealed positive results in 16 of patients using a decision tree incorporating history chest xray and either skintest or esat6cfp10 results 18 or 22 of the patients respectively were classified as latently infected with m tuberculosis four patients treated with inh because of a positive skin reaction did not show reactivity to esat6cfp10 in the whole blood assays another six patients not pretreated with inh because of negative skin tests would have received inh had the results of the whole blood assay been taken into accountconclusion the mendelmantoux skin test has a low sensitivity and specificity for the diagnosis of ltbi in this cohort of patients potentially resulting in both over and undertreatment with prophylactic inh when compared with the flow cytometric analysis of whole blood tcell reactivity to proteins specific to m tuberculosis use of tcell based in vitro tests may help to refine diagnostic testing for ltbi