there are different diagnostic methods but they have some drawbacks . to prepare mycobacterium culture , which is the golden standard for tb diagnosis , it may take 8 weeks .
finding acid - fast bacilli is the quick screening method for pulmonary tb diagnosis ; nevertheless , its sensitivity is low .
the polymerase chain reaction ( pcr ) test for tb diagnosis is expensive and it requires skilled personnel and lot of equipments .
therefore , in recent years , there has been a great demand for finding new microbiological , genetic , immunological , and biomedical diagnostic methods to diagnosis tb quickly and accurately .
ada is essential for proliferation and differentiation of lymphoid cells , especially t cells , and helps in the maturation of monocytes to macrophages .
it seems ada is an index for cellular immunity and previous studies have proved its value in tb diagnosis , even for assessing tb effusions .
, the level of ada in sputum and serum was used for diagnosis of tb , and it was monitored during tb treatment . however , previous studies used effusion fluids and a very limited number of studies used patients serum .
it is not always possible to access effusion liquids everywhere in pulmonary and extra - pulmonary tb ; therefore , it would be helpful to take advantage of serum levels .
the goal of this study is to assess the diagnostic value and cut - off point of serum ada levels in pulmonary tb patients .
it was a cross - sectional study ( 2011 ) , which is conducted in tohid hospital ( university referral hospital ) in sanandaj in iran . in our study ,
case group included 40 sputum smear - positive tb patients who were admitted in infectious disease ward of the hospital .
inclusion criteria for tb patients were :  having 2 or 3 sputum positive smears ,  or  one sputum positive smear and one positive sputum culture ,  or 
one positive tb microbe smear sputum and suspected chest radiography .  in addition , 40 non - tb patients , referred to tohid hospital in sannandaj for surgeries , were selected as the control group .
inclusion criteria for control group were : not having any tb patient in their family , not having history of close contact with tb patients , not having any infectious disease ( according to the interview and their records ) , not having fever or any symptom of illness or of being toxic , normal cell blood count , and normal chest radiography .
after diagnosis of tb ( before initiation of treatment ) , blood samples and patients approval of consent form ( research project number : 1387/87 ) were taken from tb group ( at 7 am )
. then samples were centrifuged and serum ada levels were measured by ada kit manufactured by diazyme laboratories company . in the first step , adenosine was affected by ada and it becomes de - ammonized and shifted to inosine and then ammoniac was released . in the second reaction , because of glometat , released nh3 had become dehydrogenized and when it got close to allosteric activators , it combined with nicotinamide adenine dinucleotide phosphate hydrogen ( nadph ) and released nicotinamide adenine dinucleotide phosphate ( nadp ) . consequently
, there was a direct relationship between activity ( density ) of ada enzyme and speed reduction of radiation absorption in 340 nanometer wavelength ( as nadph changed to nadp+ ) ; it was measured by diazyme adenosine deaminase assay kitt ( diazyme laboratory ; usa ) .
then , data were analyzed using statistical package for the social sciences ( spss ) 11.5 ( chicago , usa ) software and roc curve was plotted .
from all 40 tb patients who participated in this study , 16 were males and 24 were females . from 42 participants in control group , 22 were males and 20 were females .
the most common age group for tb patients was 50s and for control group , it was 40s .
age average was 59 ( 13.5 ) in tb patients and it was 49 ( 15.6 ) for non - tb patients .
the average of serum ada in tb patients group and control group was 20.88 ( 5.97 ) and 10.69 ( 2.98 ) , respectively .
u / l in which sensitivity and specificity were 92.7% ( 95% ci , 84.7 - 100 ) and 88.1% ( 95% ci , 78.3 - 97.8 ) , respectively .
the positive and negative predicative values were 88.4% ( 95% ci , 75 - 95.1 ) and 92.5% ( 95% ci , 79.6 - 98.4 ) , respectively [ figure 1 ] .
the calculated area under the roc curve was 0.955 ( 95% ci , 0.914 - 0.995 ) ( p < 0.001 ) .
in this study , serum ada level was an appropriate index for diagnosing smear - positive tb .
therefore , serum ada could be also used for diagnosis of pulmonary tb . moreover , in this study , all tb patients had a serum level of more than 22.5 u / l . hence , for suspicious cases of tb , increased levels of ada could facilitate diagnosis .
diagnostic value of serum ada in pulmonary tb has been assessed only in few numbers of studies . pairs et al . reported an increase in ada level in tb pleural effusion ; other studies have also confirmed such an increase in tb pericardial effusions , peritoneum , and central nervous system ( cns ) .
the main reason for the increased ada levels in pleural effusion is the movement of t lymphocytes toward this area .
increase in ada level is the result of a tropical inflammatory reaction caused by monocytes and macrophages .
when alveolar macrophages are infected by mycobacterium , this enzyme could be found in serum during active pulmonary disease .
when tb infection is controlled , growth - markers of lymphocytes decrease ; leucocytes will decrease in serum ada levels concurrent with the decrease in lymphocytes .
because of this , serum ada level could be utilized as a treatment response index . in agarwal
's study , ada level was 15.3 ( 0.23 ) in healthy people , 19 ( 0.68 ) in non - pulmonary tb cases , and 38.48 ( 1.56 ) in pulmonary tb patients .
in jhamaria et al . 's study , the average of serum ada level was 19.9
u / l ( 2.99 ) in control group , 43.95 u / l ( 2.48 ) in sputum smear - positive people with typical or progressive disease , and 42.09 u / l ( 1.46 ) and 40.02 u / l ( 2.58 ) in negative sputum patients with mild or typical disease . in their study , in the cut - off point of 33
it seems that as the disease progresses , ada levels increase ; this subject was not considered in our study . in another study with an ada level of 26.2 u /
l , sensitivity , specificity , and positive predictive value were 95% , 83.3% , and 79.2% , respectively . in gupta
's study , sensitivity , specificity , positive predictive value , and negative predictive value were 92.8% , 90% , 92.8% , and 90% , respectively , for diagnosis of tb in pleural effusion with an ada level of more than 40 . in conde
's study , ada level of 14 u / l was chosen as cut - off point .
stevanovic et al . assessed serums of extra - pulmonary tb patients and in a cut - off point of 24 , sensitivity and specificity were 94.3% and 92.2% , respectively ; in their study , serum ada level decreased as treatment started . in dilmac
's study , serum ada level in pulmonary tb patients was reported as 27.5 ( 11 ) and it was 23.9 ( 24 ) in chronic obstructive pulmonary disease ( copd ) patients .
in rasolinejad 's study , serum ada level was 21.51 in pulmonary tb patients and 11.47 in healthy people ; in cut - off point of 14.5 u /
u / l in negative smear and negative tuberculin patients , 33.52 ( 15.22 ) in smear - positive and purified protein derivative ( ppd ) positive patients , and 16.5 ( 3.18 ) in volunteer healthy people . such differences may be due to tb severity , age groups , genetic differences , and dissimilarities in control groups .
therefore , further studies for identifying normal ada levels in different societies may be useful .
fortunately , in some autoimmune patients like rheumatoid arthritis , synovial ada level is normal and it is similar to control group .
thus , in autoimmune diseases that involve lung , ada level could be used for tb differentiation . in some studies , ada2 was also considered a useful tool for diagnosis ; it needs further studies .
according to this study , serum ada level is proposed as a proper index for tb diagnosis ; in a cut - off point of 14 , its sensitivity and specificity are calculated as 92.7% and 88.1% , respectively .
 background : in some studies , the level of adenosine deaminase ( ada ) in sputum and effusion liquids was used for the diagnosis of tuberculosis ( tb ) . 
 but it is not always possible to access these materials . 
 the goal of this study is to assess the diagnostic value of serum ada levels in pulmonary tb patients.materials and methods : in this study , 40 sputum smear - positive tb patients who were hospitalized and 40 non - tb patients who referred for surgeries were selected . 
 a serum sample was collected and serum ada level was measured by ada kit.results:the average ( sd ) of serum ada in tb and non - tb patients were 20.88 ( 5.97 ) and 10.69 ( 2.98 ) 
 u / l , respectively ( p value < 0.05 ) . 
 the best cut - off point was 14 u / l . the calculated area under the receiver operating characteristic ( roc ) curve was 0.955 ( 95% ci , 0.914 - 0.995 ) ; sensitivity was 92.7% ( 95% ci , 84.7 - 100 ) and specificity was 88.1% ( 95% ci , 78.3 - 97.8 ) ( p < 0.001).conclusion : serum ada level may be proposed as a proper index for tb diagnosis . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS