Aim The Gold Coast Hospital receives surgical specimens from The Republic of Kiribati for processing and reporting. The specimens have prolonged fixation with formalin of unknown concentration. Conventional histopathology slides were generally inter-pretable whereas immunohistochemical staining produced widely discrepant results. In this investigation the factors affecting immu-nohistochemical staining across a range of commonly used diagnostic antibodies (vimentin, cytokeratin 7, CD34 and 45, NSE) were studied. Methods Fixation time, fixative pH and specific gravity, an indirect method of formalin concentration measurement, were performed on twenty Kiribati specimens. Immunohistochemistry was performed using optimal antigen retrieval methods and stains scored with a standard reporting system. Results The formalin in all of the 20 specimen containers was highly concentrated and markedly acidic. Staining intensity was generally weak, patchy and unreliable in all specimens across all five antibodies. Low fixative pH appeared to adversely affect staining intensity. No direct relationship with fixation time was found. Discussion Inadequately diluted and poorly buffered formalin produced unreliable immunohistochemical results. Education of Kiribati laboratory and theatre staff would improve fixation and immunohistochemistry results. The measurement of formalin concentration and pH will allow the histopathology laboratory to determine whether immunohistochemistry is appropriate for a particular specimen.
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