Abstract
For specimens that exceed the formalin fixation time recommended in the “Regulations for Handling Pathological Tissue Specimens for Genome Medical Treatment”, deterioration of nucleic acid quality is a concern. We examined the fixation conditions for maintaining good nucleic acid quality. We also examined the effect of the fixation conditions on histopathological diagnosis. We used sections of the unfixed lung, thyroid gland, and ovary as specimens. They were fixed under the following 11 conditions: “Fixed at RT for 1, 3, and 7 days”, “Refrigerated immediately after fixing and stored for 3 to 7 days”, “Fixative partially replaced with alcohol after fixing at RT for 1 day and stored at RT for 2 to 6 days”, “Fixative completely replaced with alcohol after fixing at RT for 1 day and stored at RT for 2 to 6 days”, and “Refrigerated after fixing at RT for 1 day and stored for 2 to 6 days”. Nucleic acid fragmentation was evaluated in terms of ΔCT value, and results of HE staining and IHC were also evaluated. Specimens that were “fixed at RT for 3 and 7 days” were found to have QC values below the recommended values. Under conditions other than “fixed at RT for 3 to 7 days”, the QC value was equivalent to that under “fixed at room temperature for 1 day”. For both HE staining and IHC, there was no problem with the staining results under all the set fixation conditions. It was considered that good nucleic acid quality could be maintained except for “fixed at RT for 3 to 7 days”. It was also shown that these fixation conditions do not adversely affect the histopathological diagnosis.
