Across your desk come the notes of a patient just diagnosed with multiple sclerosis under your care. Pinned to the front is a laboratory report saying her antinuclear antibody (ANA) is positive. It is not clear why the test was done or who arranged it. Does that mean your patient has lupus? Or ‘lupoid sclerosis?’ Does it matter anyway? What should you do?
WHAT DOES A ‘POSITIVE ANA’ MEAN?
The traditional test of an antinuclear antibody is an indirect immunofluorescence test of the binding of serum to the nuclei of Hep-2 cells. The result is read as the greatest dilution at which binding to the cells is still visible: the greater the dilution (titre) the higher the concentration and/or affinity of the antibody. Some laboratories give the titre itself; others (trying to be helpful) report ‘positive’, ‘strongly positive’ and so on. The pattern of binding (‘nucleolar’, ‘homogeneous’) is also sometimes
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