How much tissue is present in archival paraffin blocks and slides?

In order to inform the debate about tissue blocks and slides introduced by the Retained Organs Commission, a study is undertaken to determine the percentage weight of tissue present in the surgical archive in the cellular pathology department of a district general hospital. When original, unprocessed tissue weight is expressed as a percentage, based on the weight of 100 archival paraffin blocks, values range from 0.2% to 41.5%. When the corresponding archival slides are also included, the values fall as low as 0.1% (i.e. up to 99.9% of the stored archival material for a piece of processed tissue could be non-human material). The results are used to make a case for including archival histological material as part of the patient's clinical record, although it is accepted that this study was performed only on surgical tissue.