Special Feature: Saliva as an emerging diagnostic biological fluid

243 Saliva is a clear, slightly acidic (pH 6.0-7.0) and hypotonic exocrine secretion of major and minor salivary glands. The daily production of saliva in a healthy adult ranges from 0.5-1.5 L, with a flow rate of approximately 0.5 mL/minute. 1 Lubrication and protection of oral tissues, perception of taste, buffering capacity, and digestion of carbohydrates are some of the important functions of saliva. 2 Components of saliva include water, electrolytes and organic molecules such as amino acids, proteins and lipids. 3 The different components interact and are responsible for the functions attributable to saliva. Traditionally, systemic diseases are diagnosed based on patient's symptoms, medical history and examination and analysis of blood and/or other biological fluids. 4 Saliva samples are usually collected on suspicion of presence of oral pathology and saliva based diagnostics are used for oral diseases such as periodontal diseases and studying the risk of caries. However, in recent times, saliva is also being considered as an additional means of diagnosis of systemic diseases as a replacement for blood. This is because similar or almost identical information can be obtained from analysis of saliva, which is easy to collect and does not require invasive procedures of drawing of blood sample.4 The identification of saliva to be functionally equivalent to serum in reflecting the physiological state of the body, including emotional, hormonal, nutritional and metabolic variations has further enabled the researchers to test its usefulness in diagnosing systemic diseases. 5 However, salivary composition is influenced by the method of collection and stimulation of salivary flow. 2 Saliva can be collected under unstimulated conditions or stimulated conditions. 6 Unstimulated