HK experts establish cut-off value for pleural fluid adenosine deaminase for diagnosis of TB pleural effusion
Experts from Hong Kong recently established a diagnostic cut-off value for pleural fluid adenosine deaminase (pfADA) for the diagnosis of tuberculous pleural effusion (TBPE) by restricting analysis to a level of ≤100 U/L.
The retrospective study showed that at a diagnostic cut-off value of 26.5 U/L, the sensitivity of using pfADA levels to diagnose TBPE was 87.3 percent with a specificity of 93.2 percent and accuracy reaching 91.9 percent. [Hong Kong Med J 2018;24:38-47]
The retrospective review of 860 patient medical records from January to December 2011 showed that using the cut-off value of 26.5 U/L resulted in an increased positive predictive value (PPV) of 79.2 percent and a reduced negative predictive value (NPV) of 96.1 percent.
“Using local data, we demonstrated that TBPE was unlikely when pfADA level was more than 100 U/L. Restricting analysis to patients with pfADA levels of ≤100 U/L with negative findings for malignancy and non-tuberculous infection in pleural fluid increased the PPV and reduced the NPV,” the authors said.
The causes of pleural effusion in the 860 patients were malignancy (23 percent), TBPE (18.3 percent), congestive heart failure (16.2 percent), non-tuberculous parapneumonic effusion (11.3), and uncertain diagnosis (8.4 percent).
Among these five, the median pfADA level was highest in the TBPE group (44 U/L), followed by non-tuberculous parapneumonic effusion (11 U/L), malignant pleural effusion (9.7 U/L), uncertain diagnosis (9.4 U/L), and congestive heart failure (4.1 U/L).
Malignant pleural effusion was established by detection of malignant cells in pleural fluid (68.7 percent). A majority of the cases were caused by lung cancer (76.8 percent).
TBPE was confirmed bacteriologically via culture (39.5 percent), clinically suggested (28 percent), or via sputum acid fast bacilli (AFB) staining (5.7 percent).
All TBPE cases had pfADA levels ≤86 U/L, with more cases of exudative vs transudative pleural effusion (24.3 vs 2.3 percent).
The prediction of TBPE using the pfADA diagnostic cut-off value was not affected by sex, age or co-morbidity.
Among patients with TBPE where closed pleural biopsy was performed, TBPE was detectable by biopsy in 76.7 percent of patients, and 94.4 percent of the patients were above the pfADA cut-off level.
“Results of the study tell us that in patients with pfADA levels of ≤100 U/L, when pfADA levels are ≥26.5 U/L with negative findings in pleural fluid for malignancy and non-tuberculous infection, it is probably appropriate to manage the patient as TBPE without additionally performing pleural biopsy,” the authors concluded.
Adenisone deaminase is an enzyme involved in purine metabolism, primarily functioning in the development and maintenance of the immune system. There are two adenosine deaminase isoforms, namely ADA1, found in most body cells, and ADA2, mostly found in plasma and serum. [Clin Exp Rheumatol 2003;21:87-90]
Studies have previously reported that determination of pfADA levels is useful in the diagnosis of TBPE with the advantages of simplicity, low cost and short turnaround time. [Southeast Asian J Trop Med Public Health 2001;32:383-389]