Comparison of three methods for measuring cigarette smoking in patients with vascular disease.

Although smoking has been identified as an independent risk factor in peripheral vascular disease, smokers do not accurately report their habit. Therefore, a cheap, non-invasive, objective method of measuring smoking behaviour in vascular surgical units is desirable. The value of end-expiratory carbon monoxide monitoring, which is both simple and inexpensive, was compared with two well-established, validated techniques (serum thiocyanate and blood carboxyhaemoglobin levels). Some 33 surgical patients with peripheral vascular disease provided samples of expired air for measurement of carbon monoxide and blood for carboxyhaemoglobin and thiocyanate levels. Carboxyhaemoglobin was the most sensitive test (90%) and had a high specificity (100%). Expired carbon monoxide was the least sensitive (60%) but had a high specificity (100%). The carbon monoxide and carboxyhaemoglobin levels correlated significantly (r = 0.829; P = 0.0001). Serum thiocyanate was relatively sensitive (80%) but had a lower specificity (70%). Conventional methods for assessing smoking behaviour have not gained widespread use because they are time-consuming, relatively invasive and require technical support. Non-invasive measurement of carbon monoxide gives immediate accurate results and is a useful inexpensive method for measuring cigarette smoking in patients attending a follow-up vascular unit.