Storage of fixed samples for transport and wax blocks

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Storage of fixed samples prior to transport to MFT

Fixed tissue samples must be stored in 0.1M phosphate buffer (pH 7.4) between 4 – 20°C (room temperature).

It is recommended that they are sent to us as soon as is feasible to the sender. Prolonged storage may affect ultrastructural detail.

Wax blocks

For certain clinical questions, a limited amount of useful information can sometimes be gained by de-paraffinising the tissue and reprocessing for EM.

Where EM examination on tissue sent in fixative has not proved possible, the requesting pathologist may choose to send formalin fixed paraffin embedded (FFPE) tissue remaining from light microscopy procedures. However, service users should be fully aware of the limitations of examining de-paraffinised tissue ultrastructurally before sending. This can be advised on a case by case basis if necessary.

Again, the quality and reliability of the ultrastructural review is dependent on the quality of initial Formalin fixation and tissue processing.

FFPE tissue sent for EM should not be that which may have been frozen and used for immunofluorescence procedures prior to being fixed. Similarly, the sending of FFPE tissue which may have originally travelled from the ward/clinic to the laboratory in saline or similar solution is strongly discouraged.


(Last reviewed 19th June 2018)