Questionnaire and biochemical measures of smoking were studied in 211 hospital outpatients. Eleven different tests of smoke intake were compared for their ability to categorize smokers and nonsmokers correctly. The concentration of cotinine, whether measured in plasma. saliva. or urine, was the best indicator of smoking. with sensitivity of 96-97 per cent and specificity of 99-100 per cent. Thiocyanate provided the poorest discrimination. Carbon monoxide measured as blood carboxyhaemoglobin or in expired air Introdluction Self-reports of smoking status may not always be reliable, particularly in situations where smokers feel under strong pressure to give up smoking but have not been able to achieve this.'-3 A number of biochemical markers have been used to validate claims of nonsmoking, including measures based on thiocyanate,4-7 nicotine,8 cotinine,9-" and carbon monoxide.4 6"" These measures differ widely in availability, cost, and ease of administration. Measures based on nicotine have the advantage of being specific to tobacco but require expensive laboratory instrumentation. Levels of thiocyanate and carbon monoxide are easier to determine but may be raised through exposures unrelated to smoking, such as traffic emissions and diet. Few studies have attempted to compare the various biochemical tests." We report here a study in which all the markers of smoking currently in widespread use are compared for their ability to categorize smokers and nonsmokers correctly. Methods SubjectsThe subjects for the study were 215 outpatients at St.Mary's Hospital, London. On arrival for their clinic appointment, they were asked to fill in a self-completion questionnaire giving details of smoking habits and to provide samples of blood, expired air, saliva, and urine. There was no prior warning of the survey, but consent for the biochemical tests was obtained before completion of the questionnaire. gave sensitivity and specificity of about 90 per cent. Sensitivities of the tests were little affected by the presence among the claimed nonsmokers of a group of 21 "deceivers" who concealed their smoking. It is concluded that cotinine is the measure of choice, but for most clinical applications carbon monoxide provides an acceptable degree of discrimination and is considerably cheaper and simpler to apply. (Am J Public Health 1987; 77:1435-1438 cigarette smokers at some time and 90 (43 per cent) said that they were current smokers of cigarettes, pipes, or cigars. Reported mean cigarette consumption in the cigarette smokers was 13.2 cigarettes per day, and 97 per cent reported having smoked on the test day. with a mean time since last cigarette of 1.5 hours.The concentration of nicotine and cotinine in plasma, saliva, and urine was determined by gas chromatography.'3"14 Carboxyhaemoglobin concentrations were measured with an IL282 CO-Oximeter and carbon monoxide in expired air after breath-holding with a portable CO analyzer incorporating an ethanol filter.'5 Thiocyanate was measured by an automated modification of the A...

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This article describes the patterns and effects of maternal snuff use, cigarette smoking and exposure to environmental tobacco smoke during pregnancy on birthweight and gestational age, in women living in Johannesburg and Soweto in 1990. A cohort of 1593 women with singleton live births provided information about their own and household members' usage of tobacco products during pregnancy. The women completed a questionnaire while attending antenatal services. Data on gestational age and birthweight were obtained from birth records. Women who smoked cigarettes or used snuff during pregnancy accounted for 6.1% and 7.5% of the study population respectively. The mean birthweight of non-tobacco users was 3148 g [95% CI 3123, 3173] and that of the smokers 2982 g [95% CI 2875, 3090], resulting in a significantly lower mean birthweight of 165 g for babies of smoking mothers (P = 0.005). In contrast, women using snuff gave birth to infants with a mean birthweight of 3118 g [95% CI 3043, 3192], which is a non-significant (P = 0.52) decrease (29.4 g) in their infants' birthweights compared with those not using tobacco. A linear regression analysis identified short gestational age, female infant, a mother without hypertension during pregnancy, coloured (mixed racial ancestry), and Asian infants compared with black infants, lower parity, less than 12 years of education and smoking cigarettes as significant predictors of low birthweight, while the use of snuff during pregnancy was not associated with low birthweight. The snuff users, however, had a significant shorter gestational age than the other two groups of women. The birthweight reduction adjusted for possible confounders was 137 g [95% CI 26.6, 247.3 (P = 0.015)] for cigarette smokers and 17.1 g [95% CI -69.5, -102.7, P = 0.69] for snuff users respectively, compared with the birthweight of non-tobacco users. Among women who did not smoke cigarettes or use snuff, exposure to environmental tobacco smoke did not result in significant effects on the birthweight of their infants. In conclusion, infants of cigarette smokers had significantly lower birthweights than those of non-tobacco users or snuff users who are exposed to nicotine during pregnancy. Passive smoking did not affect birthweight significantly in this population.

The relationship between cigarette yields (of nicotine, tar, and carbon monoxide), puffing patterns, and smoke intake was studied by determining puffing patterns and measuring blood concentrations of nicotine and carboxyhaemoglobin (COHb) in a sample of 55 smokers smoking their usual brand of cigarette. Regression analyses showed that the total volume of smoke puffed from a cigarette was a more important determinant of peak blood nicotine concentration than the nicotine or tar yield of the cigarette, its length, or the reported number of cigarettes smoked on the test day. There was evidence of compensation for a lower tar yield over and above any compensation for nicotine. When nicotine yield was controlled for, smokers of lower-tar cigarettes not only puffed more smoke from their cigarettes than smokers of higher-tar cigarettes but they also had higher plasma nicotine concentrations, suggesting that they were compensating for the reduced delivery of tar by puffing and inhaling a greater volume of smoke. The results based on the COHb concentrations were consistent with this interpretation. If an adequate intake of tar proves to be one of the main motives for smoking, then developing a cigarette that is acceptable to smokers and also less harmful to their health will be much more difficult.

(Accepted 11 February 1982) Blood carboxyhaemoglobin, plasma thiocyanate, and cigarette consumption: implications for epidemiological studies in smokersCarboxyhaemoglobin and plasma thiocyanate concentrations were found to be significantly eorrelated with self-reported daily cigarette consumption in 360 smokers (r=0 416 and 0 412, respectively; p <0 001). The extent to which inhalation patterns affected the intake of cigarette smoke constituents was determined from the partial correlation between carboxyhaemoglobin and plasma thiocyanate concentrations after the number of cigarettes smoked per day had been allowed for (r = 0 48). Thus 23% of the variation in carboxyhaemoglobin and thiocyanate concentrations was accounted for by the way a cigarette was smoked and a further 21% by the number smoked, a day. Furthermore, the relation between carboxyhaemoglobin or plasma thiocyanate and daily cigarette consumption was not linear but reached an asymptote at consumption rates above 25 cigarettes a day. These results suggest that by itself daily cigarette consumption will not identify those smokers most at risk and will also underestimate the dose-response relationship between smoking and selected diseases.