The lab panels for evaluating a patient with arthralgias/arthritis for lupus or connective tissue disease are costly. Once a complete blood count and erythrocyte sedimentation rate have been done, is there a step-by-step sequential approach to this workup that might avoid unnecessary testing?
—Margaret Sowada, MD, Dallas

Start with an antinuclear antibody titer. If that is positive at ≥1:320, get anti-DNA antibody and C3 complement levels. If the latter two are negative and suspicion remains high, order an extractable nuclear antigen and an anti-SS-A antibody level to put together the diagnosis of mixed connective tissue disease or Sjögren’s syndrome.
—Jack Waxman, MD (112-2)

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