Requesting and Interpreting Pathological Tests

and Aditya G. Shivane¹

(1)

Cellular and Anatomical Pathology Level 4, Derriford Hospital, Plymouth, UK

Abstract

In order to maximise the chances of getting a diagnosis from a patient’s specimen it is important that the correct tissue has been sampled, sent to the laboratory in the correct format and with the necessary clinical information. This chapter describes general and specific information about sending most specimen types to a laboratory to ensure that the pathologist has the best chance of providing a diagnosis. Particular care should be taken when undertaking muscle and nerve biopsies, which are very sensitive to artefactual damage which can limit their diagnostic value. In the investigation of a number of rare disorders specific samples and preservatives may be required, and in such cases prior liaison with the pathologist is advised. Interpretation of pathology reports should be undertaken with care, and in most cases this is best done in the context of a multidisciplinary team meeting.

Keywords

Pathology testClinical informationBiopsyCSF

In order to get the most out of any patient biopsy or fluid examination it is important that the correct sample is taken and sent to a laboratory with appropriate clinical information. If there is any doubt about what to sample, or how best to handle and send the specimen to the laboratory, always speak to the pathologist beforehand. It goes without saying that all specimens and specimen request forms should be clearly identified with patient details including name, date of birth, address and hospital reference number, to ensure that patient samples do not get mixed up (remember many laboratories receive thousands of samples each year and many of these will be from patients with similar names). The name and address of the doctor to whom the report is to be sent and the person taking the samples (if different), should also be included, along with relevant clinical information. For all specimens, if there is a likelihood of the patient harbouring a category 3 or 4 pathogen (e.g. HIV, hepatitis B or C, tuberculosis, CJD), then this should be clearly labelled on the form as ‘high risk’, so that the laboratory can take suitable precautions to minimise any danger to laboratory staff.

3.1 Neurosurgical Specimens

The majority of neurosurgical biopsies are taken from patients with tumours, and in order for the pathologist to correctly interpret the histology adequate clinical information should be provided (Box 3.1).

Box 3.1 Information to Include on Neurosurgical Request Forms

Clinical history, including neurological symptoms and signs, previous history of tumours.

Imaging findings, including site, size and appearances of tumour, speed of growth, presence or absence of contrast enhancement.

Previous treatment, including surgery, steroids, radiotherapy, preoperative embolisation and chemotherapy.

Family history of tumours or other features to suggest a familial tumour syndrome.

Steroids may cause lymphomas to undergo marked reactive change, making diagnosis difficult and radiotherapy may result in secondary tumours (often many years later) and pathological changes such as radiation-induced necrosis. Preoperative embolization may cause changes that can be confused with malignancy such as mitoses and necrosis, particularly in meningiomas.

For large specimens (e.g. lobectomy) orientation may be important and in such cases identifying neurosurgical margins clearly with a suture, and adding this information to the request form, will aid in the pathologist being able to comment on involvement of various margins (almost always involved in diffuse gliomas). Most samples are placed in formalin before sending to the laboratory, however, with increasing frequency, genetic testing of tumour samples is important, and this is generally easier to undertake on fresh or frozen tissue. Depending on the type of genetic test undertaken, ‘control’ DNA from patient’s peripheral blood lymphocytes may also be needed. Fresh tissue samples should be sent to the laboratory immediately to allow freezing before degradation occurs (unless rapid freezing facilities are available within operating theatre). It is important that the laboratory is informed in advance when sending fresh tissue, and depending on local staffing arrangements, these samples may need to be sent in normal working hours. In the case of brain biopsies taken from patients with rapidly progressive dementia where CJD is a possibility, fresh tissue is also required. In cases of rapidly progressive dementia the biopsy should include leptomeninges, and be taken from areas of contrast enhancement if possible, as this will increase the diagnostic yield of inflammatory disorders such as vasculitis. In the investigation of patients with suspected metabolic disorders, discussion with the laboratory is required beforehand. If an infective disorder is considered a possibility, separate specimens should be sent to the neuropathology and microbiology departments, latter generally requiring fresh tissue.

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