Question.

Recently, the Kappa/Lambda ISH has quit working on our decal specimens. When we first validated ISH, we tested decal specimens that stained appropriately. We use the DECAL Stat from StatLab. I did NOT do the initial ISH validation back in 2019, but as far as I know, we have not changed which Decal solution we use since then. Has anyone else experienced this problem?

Answer 1.

Decal Stat from Statlab is HCl based, therefore is not appropriate for subsequent IHC, ISH, or other molecular studies. There is lots of peer-reviewed published data, if you need to supply rationale to your pathologists. HCl is known to significantly reduce molecular assay sensitivity and cause false negatives.

Switch to either a formic-acid based decal (such as Immunocal) or EDTA-based decal and re-optimize your assay(s).

Val Tolley, HTL (ASCP), QIHC

Answer 2.

Use a formic acid based decal solution and MAKE SURE the specimen does not fix (formalin fixation) longer than 32hrs (false negatives result). Use 70% ETOH to manage the fixation time (i.e. fix for 24 hours, decal for 4 hrs, place in 70% ETOH until it gets put on the processor. Hold in 70% ETOH for weekends and holidays).

Greg