INTRODUCTION
The epidemic of tobacco use is one of the greatest challenges which is faced by global health today. Approximately 33% of the adult population is consuming tobacco in one form or the other.1 It was uncommon to find cigarette smoking throughout the world until the 1900s but a substantial increase in smoking rates was seen in many high income countries during the first half of the 20th century.2 WHO estimated that 4.9 million deaths occurred in 2002 due to association with tobacco usage.3 This death toll is rising especially in the middle and low income group while the use of tobacco is decreasing in the high income group.3 If persistence of the current smoking patterns is seen, it is estimated that smoking will kill about 1 billion
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The accuracy of this approach is limited due to conscious false reporting and inadequate recognition of true degree of exposure.16 To overcome this hurdle, various biochemical markers of cigarette smoke like carbon monoxide, nicotine, cotinine and thiocyanate have been used as measures of smoking behavior of the subject in the recent years.16 Cyanide (CN-), a potent toxic agent that inhibits the activity of cytochrome oxidase is incorporated into the human body through inhalation of hydrogen cyanide (HCN) gas produced by the combustion of nitrogen containing compounds.17 Cyanide is gradually released from its bond with ferric ion and is metabolized to thiocyanate after accepting a sulfur atom from a sulfur donor such as thiosulfate. This reaction is catalyzed by thiosulfate transferase, a mitochondrial hepatic and renal enzyme.18 Blood thiocyanate is mainly distributed in the serum and its elevated levels suggest detoxification of cyanide.19 The thiocyanate level in plasma is considered to be a good indicator of exposure to cyano-containing organic substances as thiocyanate levels are inexorably high when the plasma cyanide levels are high.18 High levels of thiocyanate are also found in saliva and the physiologic role of salivary thiocyanate maybe the antibacterial effect of hypothiocyanate which is produced by the action of salivary