The journey of a skin biopsy specimen

(Inside Aotea, November 2010)

Ever wondered what happens to a skin biopsy specimen at the laboratory? Pathologist Dr Christopher Pease explains how one is processed.

The first step

The specimen arrives at the laboratory in a water-based formalin solution, which preserves the tissue in its journey from the doctor’s clinic.

The specimen is given a barcode and details are logged into the electronic tracking system.

Test preparation

The size and characteristics of the specimen are recorded by a pathologist. The specimen is then deposited into the histology processing machine overnight, which uses a chemical process to remove all the water from the specimen. Next the dehydrated specimen is embedded in paraffin wax to support it, and encased in a small cassette.

A thin slice

Technicians use a machine called a microtome to take very thin slices of tissue from the specimen. Forceps are used used to pick up a strip of several slices, which hang off the edge of each other — a little like a daisy chain. The chain of tissue slices is floated on a warm water bath to expand the paraffin wax. This removes all the wrinkles in the slices, leaving a very even, very thin slice of tissue.A tissue sandwich

The technician selects the best sample (or samples) to use. The tissue is picked up with a glass slide, and placed into a machine which stains the tissue so cells can be seen under the microscope. Two stains are used — haematoxylin which stains the nuclei of the cell blue, and eosin which stains the cytoplasm of the cell pink.

After the machine dissolves the paraffin wax, it creates a tissue sandwich, layering the glass slide, the stained tissue and a clear thin glass coating. The slide is then ready for the final step — diagnosis.

The final step

A pathologist looks at the slide under a microscope, and makes a diagnosis. As Dr Pease says, ‘the ultimate diagnosis is made by a human with eyes’, as opposed to other tests which are machine-based. A daily meeting also gives the pathologists the opportunity to discuss results. The results of the testing are usually returned to the doctor in 3-4 days.