Dark immunofluorescence: correlation with serum immunoglobulin abnormalities.

Occasional serum samples (<0.5%) tested by indirect immunofluorescence showed less fluorescence than did negative-control serum. A retrospective review of these patients' serum immunoglobulins revealed a high percentage of abnormalities (71%, versus 22% of controls). We suggest that this observation should be reported when seen and that the clinician should be alerted to an association with immunoglobulin abnormalities.