Serologic Testing in Connective Tissue Diseases

Abstract

Serological testing is primarily applied to assist in confirming a specific diagnosis, to formulate appropriate management strategies and, in some cases, to evaluate disease activity relative to connective tissue diseases (CTD). Based on a high index of clinical suspicion, physicians should have a compelling reason to order serologic autoantibody tests to diagnose CTD. This article is designed to serve as a guide for physicians to better understand the appropriate use and interpretation of rheumatologic tests. It is important that clinicians evaluate the indications for sensitivity, specificity, and positive and negative predicative values of serologic tests since these parameters are important in order to understand and appropriately interpret the results. The term sensitivity when used in the field of rheumatology refers to the likelihood or probability that a patient suggestive of having a rheumatologic or CTD will have a positive serologic test result. A specific serologic test is more likely to identify patients with a particular disease and exclude those without the disease. A test with a high specificity rules in, but does not rule out, a disease. A positive test result provides additional supporting evidence that the disease in question is present. Positive and negative predictive values of a test refer to the proportion of persons who test positive or negative and who have or do not have a disease, respectively. The results of these tests are highly dependent upon the prevalence of disease in the population being tested. In a population with a low prevalence of CTD, a positive test result is more likely to be a false positive.