Table 2 Main modifications occurring in the protocols of fixation, inclusion, diaphanization and microtomy that can lead to endogenous contamination by DNA
Protocols | Protocol modifications | Consequences |
|---|---|---|
Fixation | Inaccuracy in the observation of ideal tissue / formalin volume. | Defective fixation. Free loose cells in the solution (inter-samples). |
Decrease in the time required for fixation. | ||
The use of the fixative longer than indicated by the manufacturer. Presence of circulating residues from previous plants. | Presence of circulating residues from previous samples. | |
The Personal Protective Equipment (PPE) not utilized by the handlers. DNA contamination of the manipulator or other component. | DNA contamination from the manipulator or other component. | |
Diaphanization | Inaccurate observation of the ideal volumes of alcohol solution within different concentrations. | Mixture of different alcohol solutions, increasing the risk of fragment exchange. |
A rapid transfer from one alcohol solution to another. | ||
Inclusion | The quality of the paraffin. PPE not utilized by the handlers. Contamination by saliva. Cells come from previous inclusions. | Cells derived from previous inclusions. |
Cells from the saliva of the manipulators. | Cells from the saliva from the manipulators. | |
Microtomy | Reuse of razors for DNA cutting. | Transfer of DNA from the manipulator to the material (touch). |
Incorrect block manipulation. Contamination by saliva. | ||
Histological slices | Incorrect handling. Transfer of DNA from the manipulator to the material (touch) | Transfer of DNA from the manipulator to the material (touch) |