Abstract: Objective To evaluate the clinical value of detection of M.tuberculosis( M T B) D N Ain peripheral bloodlymphocyte fraction ( P B L F)for identifying patients with active tuberculosis. Method Polymerase chain reaction( P C R)technique was used to am plify 123bp and 245bp D N Afragment of M T Bin lymphocyte fraction separated from peripheralblood and in blood plasma sim ultaneously . The duration needed for elimination of M T B D N Ain P B L Fof patients with ac tive tuberculosis was investigated . Results It was verified again that,patient with active tuberculosis have M T B_ D N Aintheir P B L F,but notin plasma . The sensitivity of detecting M T B_ D N A123bp is 91.3 % (137/150) ,and 245bp is 83.3 %(125/150) . The particularity of detecting M T B_ D N A 123bp is 100 % (50/50) ,and 245bp is 92.0 % (46/50) . In 3month before end of the treatmet course, M T B were not found in sputu m smear in any of 30 initial treated patients withactive tuberculosis ,at same time thelesion in theirlung became steady . The M T B_ D N Ain P B L Fin 4 of 30 initialtreatedpatients became negative on the 6th month oftreatment course ,in 23 of 30 ,on the 9th month ,and in 3 of 30 ,on the 12thmonth . To our surprise ,the M T B_ D N Ain 25 of the 30 patients reverted to be negative within 3 months follow up . The M T B_ D N A123bp in P B L F was negetive in all persons without active tuberculosis but with positive P P Dskin test(includ ing 10 cases who were suffering from other diseases ,30 people whose tuberculosis had been cured for three years , 11healthy persons) . Conclusion Since the presence of M T B_ D N Ain P B L Fin cured patients cannot lase for a long time ,wesuggest that P C Rassay of M T B_ D N Ain P B L Fcould be used to determine active tuberculosis and to monitor the efficacyofthe treatment of tuberculosis.

Key words: Tuberculosis, Diagnosis, Poly merase chain reaction, Lym phocyte fraction