[Clinical utility of specialized immunologic testing in rheumatology in a secondary level hospital in Mexico]

Introduction Laboratory tests have an important role in rheumatology for evaluation, diagnosis, and follow up in several diseases. Specialized tests such as antinuclear antibodies (ANA), anti single, or double stranded DNA antibodies (anti-DNA), and anticardiolipin antibodies (ACL) are frequently used and its diagnostic performance is well known in tertiary care centers. Our setting is a secondary care center that implemented these tests 2 years ago. After 1 year of implementation, we decided to evaluate the frequency of use, who orders these tests, and their diagnostic properties for the diagnosis of systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APLS). Patienst and method All patients with clinical charts and a request for these tests were evaluated from September 1, 2005 to June 30, 2006. These evaluations were done prospectively by a single, trained evaluator following a standardized format looking at pretest clinical information such as pretest diagnosis, physician's level of training, service, and posttest results as well as therapeutic changes after results. Statistical analysis: descriptive statistics and 2 by 2 tables to estimate diagnostic performance of most common indications. Results Two hundred and eighty-six requests were reviewed and only 157 were evaluated. Rheumatology and Internal Medicine services sent 63 and 31 requests for these tests respectively. Diagnostic properties of ANA for SLE were sensitivity (sen) 70%, specificity (spec): 92%, positive predictive value (PPV): 81%, negative predictive value (NPP): 86%, positive likelihood ratio (PLR): 8.73, and negative likelihood ratio (NLR): 0.33. Anti-double stranded DNA, Sen: 78%, spec: 50%, PPV: 80%, NPP: 46%, PLR: 1.56, NLR: 0.44; ACACL y Sen: 78%, spec: 92%, PPV: 78%, NPV 92%, PLR: 10, NLR 0,24. Conclusions These specialized tests are not frequently used in our setting. Their diagnostic properties are not as accurate as those published in medical literature. Guidelines are needed in our hospital to improve their diagnostic performance.