ADENOSINE-DEAMINASE (ADA) ISOENZYME ANALYSIS IN PLEURAL EFFUSIONS - DIAGNOSTIC ROLE, AND RELEVANCE TO THE ORIGIN OF INCREASED ADA IN TUBERCULOUS PLEURISY

The rise in adenosine deaminase (ADA) activity in the pleural fluid of tuberculous pleurisy patients, though used for diagnosis, is of unkno wn origin. In this work, we determined ADA activity and the activities of 2'-deoxyadenosine deaminase and ADA-2 in 350 patients. We also con sidered whether the results throw light on the origin of high pleural fluid ADA in tuberculous pleurisy and estimated the diagnostic efficie ncy of 2'-deoxyadenosine deaminase, ADA-2 and total ADA activities wit h and without the inclusion of the 2'-deoxyadenosine deaminase/ADA act ivity ratio in a combined criterion. The 350 pleural effusions were cl assified by previously established criteria as transudates (60 males/1 8 females) or as tuberculous (49 males/27 females), neoplastic (50 mal es/39 females), parapneumonic (36 males/19 females), empyematous (11 m ales/3 females), or miscellaneous (25 males/13 females) exudates. Tota l ADA, ADA-2 and 2'-deoxyadenosine deaminase activities were, respecti vely, 127.5+/-2.9, 103+/-29.5 and 42.8+/-14 U . L(-1) in tuberculous e xudates. With diagnostic thresholds of 47, 40 and 22 U . L(-1) respect ively, the sensitivities of ADA, ADA-2 and 2'-deoxyadenosine deaminase for tuberculosis were 100, 100 and 95%; their specificities 91, 96 an d 92%; and their efficiencies 93, 97 and 93%, respectively. One hundre d and one effusions (all 76 tuberculous, 12 neoplastic, 4 parapneumoni c and 9 empyematous exudates) had total ADA levels >47 U . L(-1); of t hese, 8 neoplastic, 1 parapneumonic and all the tuberculous exudates h ad a 2'-deoxyadenosine deaminase/ADA activity ratio <0.49. The criteri on of simultaneously having ADA >47 U . L(-1), ADA-2 >40 U . L(-1) and a 2'-deoxyadenosine deaminase/ADA activity ratio <0.49 was satisfied by all the tuberculous effusions but only eight others (all neoplastic ) (sensitivity 100%, specificity 97%, efficiency 98%). We conclude tha t: 1) high total ADA activity in tuberculous pleural effusions is due mainly to an increase in ADA-2, and, therefore, originated from the on ly known source monocytes and macrophages; 2) ADA-2 was a more efficie nt diagnostic marker of tuberculous pleurisy than total ADA activity, although the difference was not statistically significant; and 3) amon g effusions with high total ADA the 2'-deoxyadenosine deaminase/ADA ac tivity ratio differentiates tuberculous effusions from empyemas and pa rapneumonic effusions, but fails to discriminate well between tubercul ous and neoplastic effusions.