What shall we miss if the specimens are not transported in dry ice or freezing in liquid nitrogen?
Frozen tissue is used in the evaluation of muscle biopsies, since most further testing can be performed on frozen tissue. This includes routine histology and enzyme histochemistry, immunostains, and biochemistry, including Western blots and molecular studies of DNA or mRNA.
In order to prepare frozen tissue in the laboratory the muscle biopsies are transported immediately to the lab fresh at room temperature, either wrapped in gauze lightly moistened in saline or wrapped in cling film to prevent drying out. The total transit time less should be less than two hours from the time of collection. Once the specimen reaches the lab it will be frozen with liquid nitrogen and processed further. Samples with transit time exceeding two hours must be frozen on site and transported on dry ice.
Delays in fixation of any specimen can lead to autolytic changes in the tissue, which can affect the morphology. Additionally, if the specimen is immersed in saline, it will have excessive moisture which can lead to freezing artefact with formation of ice crystals. If the freezing process is slow, it too can lead to freezing artefact.
Formalin fixation of muscles biopsies is reserved only for specimens in which there is a risk of infection. The preservation of muscle morphology is not as good on formalin fixed specimens, since formalin causes shrinkage of the specimen, which can interfere with the interpretation of muscle fibre size and shape. Additionally, enzyme histochemistry cannot be performed on formalin fixed tissue since it requires frozen tissue. Formalin fixed specimens can be stained with haematoxylin and eosin and immunohistochemistry. However, many antibodies and molecular studies used in the assessment of muscle biopsies have been optimized for frozen tissue so that is preferred.