Which of the following is NOT part of the routine workup for a patient suspected to have GCA?

When evaluating a patient suspected to have giant cell arteritis (GCA), a condition characterized by inflammation of the blood vessels, several laboratory tests are commonly included in the routine workup to assess for signs of inflammation and rule out other conditions. Among these tests, the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are key indicators of inflammation activity, while a complete blood count (CBC) with differential provides information about blood cells and can show anemia or thrombocytosis, which are often seen in GCA.

The antinuclear antibody (ANA) test, however, is not typically part of the routine workup for GCA. ANA is primarily used to investigate autoimmune diseases, such as lupus or Sjögren's syndrome, where the immune system targets the body's own tissues. Although a positive ANA can indicate an autoimmune process, it is less relevant for diagnosing GCA, where the focus is on confirming the presence of significant inflammatory markers.

In summary, while ESR, CRP, and CBC w/ differential are essential tools in assessing a suspected case of GCA due to their direct relevance to the inflammatory process, the ANA test does not serve as a standard component of the initial investigation into this condition