Chapter 2 Answers to discussion questions

Preparation techniques

2.1 Sampling error limits the clinical value of cytology. Critically discuss this statement.

Sampling error describes the extent to which a sample is not representative of a target tissue or lesion and should be discussed from two perspectives: specimen collection and specimen preparation. There are several sources of sampling error in specimen collection, such as difficulty in locating or visualizing the target site, faulty collection technique, or failure to transfer a sufficient quantity of a specimen to the collection vessel. Sampling error in specimen processing stems mainly from the practical difficulties of processing specimens in their entirety. The challenge for the cytologist is ensure that the cells transferred to the glass slide for subsequent examination are representative of the specimen received. When this fails, which may be due to inadequate training or the use of inappropriate equipment, diagnostic error is almost inevitable.


2.2 Discuss the benefits and limitations of automated preparation techniques in cytology.

Automated specimen processing devices can be a cost effective, time-saving and labour-saving alternative to manual techniques in cytology. However, all new automated devices require robust validation procedures to ensure they deliver reliable and accurate results. They can be expensive to purchase or rent and can incur high maintenance and repair costs.


2.3 Discuss the factors that govern the choice of fixative for cytology specimens. Why are cytological fixatives generally different from those used in histology?

Cytological fixatives should have the following properties: speed of action; inexpensive; minimum cell shrinkage; optimum nuclear preservation; and preservation of antigenic structure if immunocytochemistry is planned. Ethanol is an ideal cytological fixative but is not favoured in histology because of its poor penetration of tissues. Histological fixative formalin is not used in cytology because Papanicolaou staining results are generally poor.


2.4 Cytologists are trained to examine cell preparations under the microscope for alterations in cell morphology that might indicate disease. Cytologists are therefore morphologists by training. Suggest how the skills of the cytologist might need to change in the future, given that the range of cell demonstration techniques is becoming increasingly diverse.

There is likely to be an increasing need for cytologists to be skilled in the techniques of molecular biology. The ability to interpret the results of molecular tests in combination with morphological diagnoses will be an important asset for cytologists of the future.


2.5 Most cytology laboratories are built to containment level 2 standard. Discuss how this can be justified, given that the hazard group to which microorganisms in clinical specimens belong is usually not known.

It is recognized that pathogens may be present in specimens which, if they were already identified, would need to be handled at a higher level of containment. If it becomes apparent that group 3 or 4 pathogens are being handled in a containment level 2 laboratory then all further work on the specimen(s) must be undertaken at the appropriate higher level of containment. However, certain pathogens need not always be handled at the containment level corresponding to their allocated hazard group. The group 3 pathogens human immunodeficiency virus (HIV) and the hepatitis viruses are cases in point. Although these organisms belong to hazard group 3 it is acceptable for specimens containing these organisms to be handled in containment level 2 facilities, provided certain additional precautions are taken and that a full risk assessment is carried out. Advice from safety specialists is usually required in such circumstances.

Back to top