According to CAP how long should you be retaining your records and materials? ANP 12500, the CAP checklist item on record retention, says that they must be retained for an appropriate period. This may vary depending on the rules of your institution or your state, but CAP does set a minimum for this appropriate period.
Accession log records - 2 years
Wet tissue - 2 weeks after final report
Paraffin blocks - 10 years
Glass slides - 10 years (slides must remain readable for this time)
GEN.20377 of the CAP checklist also sets a guideline for retention of quality control records, stating that the documents should be kept for a minimum of 2 years. Quality control slides would fall under glass slide regulations and be kept for 10 years.
(CLIA laboratory record retention requirements also suggest keeping slides for 10 years and most records for 2 years.)