IZVG Pathology
Collecting and submitting specimens for histological examination
Guidelines to ensure that you get maximum benefit from each specimen
Please note that new packaging regulations now apply to diagnostic samples.
Collection and fixation:Take samples as soon as possible after death, and transfer to fixative as soon as practical. If there is a delay before specimen collection, store the carcass in a refrigerator. Do not freeze; ice crystals will disrupt histology.
Use only fresh supplies of buffered formaldehyde solution of the correct concentration (4% in phosphate buffered saline, pH 7.2 to 7.4. Stock solutions of formaldehyde are typically 40%, pH 3 or 4). Non-buffered or the wrong concentrations of formaldehyde cause poorer fixation and precipitate formalin pigment in tissues, which can confuse analysis. In tropical conditions, fixative should be kept cool to prevent deterioration.
Use enough fixative. The volume of fixative should be ten times the volume of the tissue to be fixed. Samples should be added to fixative, and not vice versa, so that they do not stick to the side of containers. If samples are to be sent by post and weight is an issue, it is better to place the samples in a large volume of fixative for 24 hours, then transfer to a small volume for transport.
Samples thicker than 0.5–1 cm will not fix adequately at their centre, because the formaldehyde cannot penetrate through. Where an obvious lesion is observed, take a slice through this, and a separate slice of the “normal” organ, rather than squeezing the whole organ into a pot.
If entire animals, such as fish, are to be sent, open up the body cavities with a single ventral midline incision, to allow access by fixative.
When submitting large pieces of tissue, partially slice them at 0.5 to 1 cm intervals to allow fixative penetration but so that the receiving pathologist can reconstruct them. The heart and brain are the only exceptions. The heart should be submitted whole if possible, particularly if cardiovascular disease is suspected. Open the chambers and wash out clotted blood to assist fixation. The whole heart enables valves, conduction system and adaptive changes to be assessed. Brain is also best removed whole and fixed by immersion. Brain tissue requires fixation before it can be sliced systematically to detect subtle lesions.
Muscle, skin and nerve biopsies may require special treatment. Please contact the pathologist if in doubt.
Pathological samples are classified as Dangerous Goods, and must be transported in accordance with UN Regulations. It is important that you follow the packaging guidelines when packing your samples. Failure to do so could result in Royal Mail postal service, or courier companies, refusing to carry your samples.
*Please note that the terms Pathological or Diagnostic Specimen are now obsolete, and are replaced by “UN3373 Biological Substance Category B” which must be marked on all packages containing pathological samples*
Please contact the office for information on suitable packaging materials for samples. Appropriate packaging kits can be supplied to clients for a small cost.
- Identification and clinical history must accompany specimens. Submission forms, designed to give us all of the information we need, are available, and it is very helpful if these are completed as far as possible. We ask for different information for fish or other aquarium species, so please fill in the aquarium form.
We are always delighted to hear by telephone (01535 692000) or e-mail about particularly urgent samples, special requests or clinical developments that may affect interpretation.
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