If a patient's serum shows a positive speckled pattern in an anti-nuclear antibody test, what additional test should be performed?

A positive speckled pattern in an anti-nuclear antibody (ANA) test is typically indicative of several potential autoimmune diseases, including systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD). The next step is to perform more specific antibody tests to identify the underlying condition.

Screening for Sm (Smith) and RNP (ribonucleoprotein) antibodies is particularly relevant because these antibodies are associated with specific diseases linked to a speckled ANA pattern. Sm antibodies are highly specific to systemic lupus erythematosus, while RNP antibodies can indicate a mixed connective tissue disease, which often presents with a speckled ANA pattern. The presence of these antibodies can provide critical information for diagnosing and managing a patient's condition.

In contrast, other antibodies, such as anti-histone antibodies, may be more associated with drug-induced lupus and not as specific for conditions represented by a speckled ANA pattern. Similarly, anti-DNA antibodies are more specifically linked to SLE but usually show a homogeneous pattern, and anti-centromere antibodies are typically associated with scleroderma, which might show a specific centromere pattern rather than a speckled one. Thus, testing for Sm and