7: Investigations



Informed consent and confidentiality are required for all investigations, and the advantages should clearly outweigh any dangers or disadvantages.

Blood tests

Blood tests can help determine disease states, but should be requested only when clinically indicated. There is always a danger of needlestick injury. Furthermore, abnormal ‘blood results’ do not always mean disease and false-positive results are possible. Serum is used for assaying antibodies, which can help diagnose infections and autoimmune disorders, and for assaying most biochemical substances (e.g. ‘liver enzymes’).

Microbiological tests

Microbiological diagnosis is based on either demonstration of the microorganism or its components (antigens or nucleic acids) directly in samples or tissues, which are best used as results are speedily obtained. The demonstration in the serum of a specific antibody response can be helpful.

Salivary flow determination

Unless the baseline salivary flow rate for an individual patient is known, it is impossible to be certain if there has been a reduction in salivary flow, since the salivary flow rate varies widely from person to person. Salivary flow rates also vary over time and so estimates should be taken on several occasions.

Normal and reference values are shown in Table 7.1.

Table 7.1

Whole saliva flow rates* (ml/min)

  Normal Hyposalivation
Unstimulated (resting) 0.3–0.4 ml/min <0.1 ml/min
Stimulated 1–2 ml/min <0.5 ml/min

*Unstimulated salivary flow rate (USFR) measurement of whole saliva uses a simple draining test for 5 minutes at rest: a rate less or equal to 0.1 ml/min suggests hyposalivation.


Before beginning, it is important to decide whether an excisional or incisional biopsy is indicated.

Excisional biopsy

Excisional biopsy (Figures 7.17.4) is used for small superficial lesions (max 1 cm). If a malignant tumour is suspected, even if small, an excisional biopsy must be done by a specialist.

Figure 7.1 Instrumentation for excisional biopsy. Shown are: retractor, aspirator, surgical blade No. 15, surgical forceps, scissors, sutures (catgut or silk 3 or 4), two needle holders, LA (local anaesthetic) syringe and anaesthetic, blotting paper.
Figure 7.2 (A, B) Excisional biopsy must be used for small superficial lesions (max 1 cm).
Figure 7.3 (A, B) Remove the tissue completely.
Figure 7.4 Finally, after achieving haemostasis, suture.

Incisional biopsy

Choose the area to biopsy based on:

• appraisal of the clinical appearance (red areas rather than white)
• vital staining with toluidine blue.

An incisional biopsy (Figures 7.57.13) can be performed with a scalpel, or dermatology punch.

Figure 7.5 Simple incisional biopsy. This is indicated in homogeneous lesions, such as white papules or plaques.
Figure 7.6 A simple incisional biopsy can be made not only in homogeneous lesions but also in red or erosive areas.
Figure 7.7 A mapping incisional biopsy consists of taking several specimens from different areas. It is usually carried out in non-homogeneous lesions.
Figure 7.8 The incisional biopsy may be preceded by vital staining with toluidine blue (see above). It consists in biopsying several stained areas (royal blue ones). It is carried out in non-homogeneous lesions with extensive red areas.
Jan 12, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 7: Investigations
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