Abstract

The quality of any laboratory test result is highly dependent on the quality of the collected sample and how it is handled before and during submission; as well as the appropriateness of the specimen for the particular assay. Sample quality is dependent on proper collection, handling, storage, packaging, and timely transport under environmental conditions that will maintain sample integrity. The purpose of this presentation is to review best practices for sample handling and submission for histopathology and molecular diagnostics and provide tips on avoiding common pitfalls that can affect results.

Histopathology

A standard tissue set representing all organs should be submitted from all necropsy cases, including brain and reproductive tract. Tissues should be <1 cm thick and the formalin to tissue ratio 10:1. Whenever possible, submitting the entire brain for histologic evaluation is preferred. For large brains fixing in a separate container is essential and the formalin may need to be refreshed to obtain proper fixation. The heart should not be submitted whole in formalin but be sectioned appropriately to obtain sections of the left and right walls and interventricular septum.

Labelling of every tissue or submitting tissues in separate containers is generally not necessary. Labelling of lesions can enable the pathologist to relate findings to gross abnormalities. Unless lymph nodes are submitted with adjacent tissue (i.e., tracheobronchial node with trachea), nodes should be labelled. A common mistake is to submit numerous lymph nodes but only single sections of major lesions or organs. Laundry tags are useful for tissue labelling. Tissue cassettes should only be used for very small biopsy samples. A complete history, gross necropsy report, and post-mortem photos should be concurrently provided to the pathologist.

Molecular Diagnostics

Most laboratories have written submission guidelines that should be referenced to guide sample collection, handling, and transport. Understanding the sample type and amount required for the desired assay is essential and should be reviewed prior to specimen collection. Direct communication with laboratories is recommended to maximize diagnostic testing yield. Lab personnel are often willing to discuss sampling plans prior to diagnostic procedures to ensure appropriate assays are selected for desired testing.

Storage and Transport

For most PCR assays a minimum of 500 µl of fluid and 50 mg of tissue (pea-sized) is required. For PCR on whole blood, samples collected into heparin or EDTA samples are typically acceptable. Tissue should be placed in sterile cryovials or whirl packs. Swabs should be placed in cryovials and not in bacterial culturettes as culture media can inhibit PCR.

Frozen samples should be shipped with adequate amounts of dry ice. Formalin samples should be in tightly sealed, leak proof, primary containers and packaged and shipped in accordance with IATA regulations. Formalin samples should not be frozen. Once samples have been adequately fixed the formalin amount can be reduced for shipping. Vacuum sealed bags are highly useful for transporting and storing formalin fixed tissues.

Informing laboratories of pending shipments and providing a tracking number is recommended in order to troubleshoot shipping delays.

* Presenting author