tumor necrosis factor  ( tnf ) is a regulating cytokine with a central role in the pathogenesis of chronic inflammatory disease and thereby a well - defined target for intervention . in concordance with this , inhibitors of tnf have become increasingly important in treatment of a broad spectrum of rheumatic diseases such as rheumatoid arthritis , psoriatic arthritis , ankylosing spondylitis , juvenile inflammatory arthritis , adult onset still s disease , and sarcoidosis . however , tnf is also an essential component of host defense against pathogenic viruses , bacteria , and fungi , and therapeutic inhibition of tnf may elicit risk of opportunistic infections [ 7 , 8 ] , in particular , tuberculosis [ 9 , 10 ] . thus , screening for ltbi before tnf inhibition has been recommended , however , no gold standard for detecting ltbi exists today and guidelines have provided conflicting recommendations about the place of diagnostic screening tests such as tuberculin skin test ( tst ) and interferon - gamma release assay ( igra ) . firstly , tst attempts to measure cell - mediated immunity by delayed - type hypersensitivity response to purified protein derivate ( ppd)i.e . , a crude mixture of mycobacteria antigens . this results in false positive results in non - tuberculosis mycobacterium infection and clinically more important , in bacillus calmette  gurin ( bcg)-vaccinated persons [ 11 , 12 ] . secondly , tst sensitivity is lower in immunocompromised patients , possibly due to impaired t cell function and impaired cellular immunity . and thirdly , tst has practical disadvantages such as inconvenience ( two patient visits ) and interobserver variability . with respect to these limitations , an in vitro t cell - based assay has been developed , detecting interferon - gamma in response to contact with antigens highly specific for tuberculosis mycobacteria ( esat-6 , cfp-10 , and tb 7.7 ) . this igra is not influenced by contact with non - tuberculosis mycobacteria or prior vaccination with bcg [ 15 , 16 ] . moreover , it is suggested that igra has higher sensitivity in comparison to tst in patients receiving immunosuppressive treatment [ 13 , 17 , 18 ] . in summary , although some evidence exists that igra has a better performance in screening of ltbi before starting tnf inhibition , the true value of igra as a diagnostic tool , with respect to tst , is ill - defined . the objective of this study was to compare tst and igra ( quantiferon - tb gold ) in detecting ltbi in refractory inflammatory disease patients prior to the initiation of a first tnf inhibitor . between 2008 and 2009 , we prospectively enrolled patients with chronic immune - mediated inflammatory diseases starting on tnf inhibition . patients were recruited from the rheumatology outpatient clinic of the medical center of leeuwarden , the netherlands . patients with rheumatoid arthritis , ankylosing spondylitis , psoriatic arthritis , and juvenile idiopathic arthritis ( fulfilling american college of rheumatology criteria ) , and two patients with sarcoidosis and still s disease refractory to treatment with corticosteroids and methotrexate , were included . the decision to start tnf inhibition was made in agreement with criteria of the dutch society of rheumatology . the following variables were collected : gender , age , diagnosis , disease duration , and immunosuppressive treatment ( type and dosage ) at study inclusion . tuberculosis exposure was assessed by personal and family medical history , previous treatment with tuberculostatic , and bcg vaccination . patients were tested for ltbi by tst and igra ( quantiferon - tb gold ) . patients with discordant or concordant positive test results received adequate tuberculostatic treatment before initiation of tnf inhibition except for bcg - vaccinated patients with positive tst , negative igra , and negative medical history . tst was performed by intradermal injection of 0.1  ml of ppd at the flexor surface of the upper one third of the forearm according to the mantoux method . the diameter of skin induration was assessed 4872  h after inoculation by a trained rheumatologic nurse . a positive tst was defined as 5  mm induration according to the dutch guidelines . immediately after the intradermal injection of ppd , a heparinized whole blood sample was collected and transferred to three quantiferon - tb gold test tubes ( cellestis ltd , australia ) to prohibit a booster effect . igra was performed and interpreted according to instructions of the manufacturer and guideline of centers of disease control and prevention , respectively . an edta tube was collected for assessment of cellular immunity by cd4 cell t lymphocyte count ( cd4 cell count ) . patient characteristics twenty - nine out of 56 included patients were diagnosed with rheumatoid arthritis ( 51.8% ) of whom 83.3% were rheumatoid factor positive ( table  1 ) . other diagnoses were ankylosing spondylitis ( 30.4% ) , psoriatic arthritis ( 8.9% ) , undifferentiated spondylarthropathy ( 3.6% ) , juvenile idiopathic arthritis ( 1.8% ) , adult onset still s disease ( 1.8% ) , and sarcoidosis ( 1.8% ) . mean (  sd ) age of the total study population was 50.3    15.4  years , and disease duration was 8.7    9.2  years . about half of the study population ( 48.2% ) had received methotrexate (  corticosteroids ) , 5.4% leflunomide (  methotrexate  corticosteroids ) , 1.8% azathioprine and corticosteroids , 5% only corticosteroids , and 35.7% did not had previous immunosuppressive treatment . the incidence of bcg vaccination in the total investigated population was 5% which is representative of a post - world war ii population . tuberculosis exposure was 14% and is in line with the low prevalence of tuberculosis in western europe countries . the absence of reactivation of tuberculosis during tnf inhibition in the bcg - vaccinated patients ruled out the coexistence of bcg vaccination and prior tuberculosis exposure in this population . ( % ) male32 ( 53.6%)age ( mean    sd)50.3    15.4  yearsdiagnosis  rheumatoid arthritis29 ( 51.8% )  rf positive25 ( 83.3% )  ankylosing spondylitis17 ( 30.4% )  psoriatic arthritis5 ( 8.9% )  undifferentiated spondylitis2 ( 3.6% )  juvenile idiopathic arthritis1 ( 1.8% )  still s disease1 ( 1.8% )  sarcoidosis1 ( 1.8%)disease duration ( mean    sd )  total study population8.7 9.2  years  rheumatoid arthritis7.4    7.7  yearstype of immunosuppressive treatment ( at study inclusion )  methotrexate  corticosteroids27 ( 48.2% )  leflunomide  methotrexate  corticosteroids3 ( 5.4% )  azathioprine and corticosteroids1 ( 1.8% )  only corticosteroids ( maintenance and high - dose treatment)5 ( 8.9% )  no current immunosuppressive treatment20 ( 35.7%)daily dose of immunosuppressive treatment ( at study inclusion ; mean    sd )  methotrexate19    7  mg  leflunomide20    0  mg  azathioprine150  mgcorticosteroidsmaintenance treatment6    2  mghigh - dose treatment3,000    0  mgbcg vaccination3 ( 5%)tuberculosis exposure8 ( 14%)data are presented as number ( no . ) and percentage ( % ) and , if applicable , mean    standard deviation ( sd)no . number of patients , rf rheumatoid factordiagnosis according to the american college of rheumatology criteriaonce - only three pulses of 1  g methylprednisolone prior to ltbi screening ( n  =  3 ) patient characteristics of 56 patients data are presented as number ( no . ) and percentage ( % ) and , if applicable , mean    standard deviation ( sd ) no . number of patients , rf rheumatoid factor diagnosis according to the american college of rheumatology criteria once - only three pulses of 1  g methylprednisolone prior to ltbi screening ( n  =  3 ) comparison of tst and igra nine out of 56 patients ( 16.1% ) tested positive for ltbi with either tst or igra ( table  2 ) . a concordant positive result was present in three patients with a medical history of tuberculosis exposure . in six patients , discordant results were obtained : one patient had a negative tst and positive igra , and five patients had a positive tst and negative igra . the mother of the patient with negative tst and positive igra had suffered from tuberculosis during his childhood . the five patients with positive tst and negative igra were either bcg - vaccinated ( three patients ) or had a medical history of tuberculosis exposure ( two patients ) . the bcg - vaccinated patients with positive tst and negative igra did not develop tuberculosis during tnf inhibition in the follow - up period ( 12  years ) . table  2characteristics of nine patients with concordant positive tst and igra and discordant tst and igrantstigrabcgtuberculosis exposurecd4 count ( cells / mm)medication ( daily dose in mg)diagnosisconcordant positive results of tst and igra1pos.pos.noyes748mtx 12.5 ; lef 20psa2pos.pos.noyes972mtx 25ra3pos.pos.noyesn.a.noneasdiscordant results of tst and igra1neg.pos.noyes974mtx 15ra2pos.neg.yesno590pred 5 ; mtx 10 ; lef 20ra3pos.neg.yesno387mtx 25ra4pos.neg.yesno2,050mtx 7.5psa5pos.neg.noyes632noneas6pos.neg.noyes549mtx 7.5ran patient number , tst tuberculosis skin test , igra interferon - gamma release assay ( quantiferon - tb gold ) , bcg bacillus calmette not available , mtx methotrexate , pred prednisone , lef leflunomide , psa psoriatic arthritis , ra rheumatoid arthritis , as ankylosing spondylitis characteristics of nine patients with concordant positive tst and igra and discordant tst and igra n patient number , tst tuberculosis skin test , igra interferon - gamma release assay ( quantiferon - tb gold ) , bcg bacillus calmette not available , mtx methotrexate , pred prednisone , lef leflunomide , psa psoriatic arthritis , ra rheumatoid arthritis , as ankylosing spondylitis cellular immunity cd4 cell counts were within normal limits with a mean (  sd ) of 964    568 cells / mm ( fig .  1 ) . a cd4 cell count below 300  cells / mm was present in two patients receiving methotrexate and low - dose corticosteroids . these two patients had a negative result for tst and igra and did not develop tuberculosis during tnf inhibition ( 2  years of follow - up ) . there were no patients with a cd4 cell count below 200  cells / mm . 1cellular immunity defined by immunosuppressive treatment and cd4 t lymphocyte cell count ( cells / mm ) at study inclusion . data are given as mean    standard deviation ( sd ) cellular immunity defined by immunosuppressive treatment and cd4 t lymphocyte cell count ( cells / mm ) at study inclusion . the objective of this study was to compare tst and igra ( quantiferon - tb gold ) in detecting ltbi in refractory inflammatory disease patients prior to the initiation of a first tnf inhibitor . a well - recognized problem in screening for ltbi is absence of a gold standard and thereby sensitivity and specificity of tst and igra can not be directly measured . nevertheless , assessment of tuberculosis exposure , combined with results of tst and igra , may roughly estimate the a priori chance of ltbi . nine out of 56 patients ( 16.1% ) tested positive for ltbi with either tst or igra . a concordant positive result was present in three patients with a medical history of tuberculosis exposure . the remaining six patients with discordance had either a negative tst and positive igra ( one patient ) or a positive tst and negative igra ( five patients ) . the discordance in the five patients with positive tst and negative igra can be attributed to bcg vaccination ( three patients ) or a medical history of tuberculosis exposure ( two patients ) . as for the patients with negative igra and positive tst , it can not be excluded that igra may be false negative as the infection occurred in the distant past . this may be explained by the fact that igra mostly measures effector t cell responses whereas tst measures both effector and memory t cell responses . after 24  h incubation in the igra , only circulating effector memory t cells have sufficient time to produce interferon , while central memory t cells first started producing interferon after a more prolonged ( 72  h in tst ) incubation . the quantiferon - tb gold performs well in routine screening of low - prevalence populations , but its performance turned out to be suboptimal in healthy persons with a high risk of tuberculosis exposure . it is also known that the sensitivity of the quantiferon depends on the test and is higher for the latest in - tube version that was used in this study . ( n  =  1 ) of discordant negative tst and positive igra in a low tuberculosis - exposed population . indeterminate results of igra are commonly reported in patients with , e.g. , hiv , malignancy , and chronic renal failure , and patients undergoing immunosuppressive treatment [ 24 , 25 ] . in comparison with studies in rheumatic disease patients [ 2632 ] , it is remarkable that in this study igra could be interpreted without problems  i.e . this suggests that lymphocytes retained the capacity to produce interferon - gamma on mitogen stimulation in vitro , even with immunosuppressive treatment . although we do not have a representative control group , it appears that cd4 cell count in this study population was not greatly reduced in response to immunosuppressive treatment , cd4 cell counts were not below 200  cells / mm and only two patients had a cd4 cell count below 300  cells / mm . furthermore , the two patients with a positive tst , a negative igra and an positive medical history of ltbi had both a normal cd4 cell count . the absence of a significant influence of immunosuppressive treatment on interpretation of igra in patients with inflammatory rheumatic conditions has previously been reported by matulis . cellestis stated that as long as the viable cd4 cell count is above 200  cells / mm quantiferon - tb gold has a good performance . however , it has been questioned whether cd4 cell count can be used as a marker of validity of igra in patients other than hiv patients . furthermore , the intrinsic function of t cells may be an important precondition for the capacity of interferon production . two studies analyzing the impact of different classes of drugs on the response of tst and igra in european patients with immune - mediated inflammatory diseases stated that corticosteroid treatment can in fact compromise test results by increasing the number of indeterminate results of igra and negative tst outcomes [ 27 , 29 ] . we therefore hypothesize that high - dose corticosteroid maintenance therapy may be a risk factor for an indeterminate igra result . possibly , the absence of indeterminate test igra results in our study was due to the low - dose corticosteroids ( 10  mg per day at most ) . overall , sensitivity of igra for the diagnosis of ltbi might be higher than tst , despite a higher rate of indeterminate results in immunocompromised patients [ 2632 ] . various recommendations and guidelines have been issued to determine the place of diagnostic screening test for ltbi . two leading institutes , the centers of disease control and prevention ( cdc ) of the united states and united kingdom s national institute for health and clinical excellence ( nice ) , have developed guidelines regarding correct usage of both diagnostic tools [ 20 , 33 ] , but they came to conflicting conclusions . the cdc stated that igra is a real alternative for tst whereas nice advised the use of igra only for the validation of a positive tst . the variation in prevalence of tuberculosis over time in different parts of the world may account for this disagreement . western europe has a substantially larger bcg - vaccinated population as compared to the united states of america ( usa ) . furthermore , most cases of lbti in western europe occurred in a population born before 1945 . a lower performance of igra in europe as compared to the usa may be attributed to a low sensitivity in the case of longer duration of ltbi . in different countries of western europe igra is currently added in a second step approach according to nice or is even replacing tst ( germany , switzerland ) [ 34 , 35 ] . we feel that all physicians , including rheumatologists , who treat different immune - mediated inflammatory diseases , are obliged to hand tailor the prophylactic therapy for ltbi by the prevalence of tuberculosis and bcg vaccination of their country . in conclusion , the findings of this study suggest that igra appears reliable for confirming a positive tst and excluding a false positive result ( in case of prior bcg vaccination ) in this dutch serie of patients . igra may thereby reduce the number of patients in whom tuberculostatics are prescribed in absence of ltbi , resulting in an evident benefit of avoiding a 6-month delay of effective anti - rheumatic treatment with tnf inhibition and possible side effects due to treatment with tuberculostatics . moreover , igra seems to detect an additional case of ltbi that otherwise be missed using solely tst . igra appears not to be significantly influenced by immunosuppressive treatment , at least not by the regimen and dosage used in this study . although the number of patients is not large enough for powerful statistical analysis and patient characteristics are quite heterogeneous , this study contributes to the ongoing discussion on the diagnostic value of igra . igra should not be employed as an alternative single screening test as false negative results have been observed . confirmation in larger studies , including cost - effectiveness in different countries to determine the optimal screening strategy , is warranted .
treatment with tnf inhibitors increases risk of reactivating a latent tuberculosis\infection ( ltbi ) . 
 therefore screening , prior to therapy with tnf inhibitors , has been recommended , even in low - endemic areas such as well - developed western europe countries . 
 we evaluated interferon - gamma release assay ( igra ) , as opposed to tuberculin skin test ( tst ) , for detection of ltbi in refractory inflammatory disease patients prior to the initiation of a first tnf inhibitor . 
 in addition , we evaluated the impact of impaired cellular immunity on igra . 
 patients starting on tnf inhibition were screened for ltbi by tst and igra ( quantiferon - tb gold ) . 
 data on tuberculosis exposure and bacillus calmette  gurin ( bcg ) vaccination were obtained . 
 cellular immunity was assessed by cd4 + t lymphocyte cell count . 
 nine out of 56 patients ( 16.1% ) tested positive for ltbi . 
 a concordant positive result was present in three patients with a medical history of tuberculosis exposure . 
 six patients with discordant test results had either : ( 1 ) a negative tst and positive igra in combination with a medical history of tuberculosis exposure ( n  =  1 ) or ( 2 ) a positive tst and negative igra in combination with bcg vaccination ( n  =  3 ) or a medical history of tuberculosis exposure ( n  =  2 ) . 
 cd4 + t lymphocyte cell counts were within normal limits , and no indeterminate results of igra were present . 
 igra appears reliable for confirming tst and excluding a false positive tst ( due to prior bcg vaccination ) in this dutch serie of patients . 
 in addition , igra may detect one additional case of ltbi out of 56 patients that would otherwise be missed using solely tst . 
 immune suppression appears not to result significantly in lower cd4 + t lymphocyte cell counts and indeterminate results of igra , despite systemic corticosteroid treatment in half of the patients . 
 confirmation in larger studies , including assessment of cost - effectiveness , is required .