Pitfalls of formalin fixation for determination of antineutrophil cytoplasmic antibodies

Sera can produce nuclear or perinuclear immunofluorescence staining in neut rophils which may be caused by antibodies with differing antigenic specific ities. These include perinuclear antineutrophil cytoplasmic antibodies (P-A NCA), granulocyte specific antinuclear antibody (GS-ANA), and antinuclear a ntibody (ANA). There is controversy over the value of formalin fixation of neutrophils in differentiating antibodies giving selective or preferential reaction with the nuclear or perinuclear area of neutrophils. In a comparat ive study of 77 sera, formalin fixation caused inconsistency, nonspecific e ffects, and false positivity owing to enhanced fluorescence, If formalin fi xed neutrophils are used in the routine diagnostic laboratory, this will ad d confusion to the interpretation of the ANCA assay.