[How long will preserved blood and bone marrow films give reliable cytochemical staining?]

We tested how long unstained and unfixed films of blood and aspirated bone marrow could be kept before special cytochemical staining. To exclude influences other than time on the outcome of the reactions, all the material was taken from hematologically normal persons. A simple score was used to evaluate the results. These may be summarized as follows: in most cells Naphthol-AS-acetate-esterase first shows a progressive decline in reactivity after a delay of 6 weeks, the reaction becoming very weak after 10 +/- 1 weeks. This does not hold for monocytes, megakaryocytes and platelets, which maintain reactivity (and susceptibility to NaF) for more than three months. With PAS staining, a slight decrease in reactivity after 8 +/- 2 weeks could be observed, whereas all other stainings tested (POX, Sudan black B and Naphthol-AS-D-esterase) were unaffected even by a delay of up to 16 weeks.