Controversies in spirometry

Dr. Benjamin Chan and colleagues have identified regional variations in spirometry use in Ontario physicians' offices ("Spirometry utilization in Ontario: practice patterns and policy implications," Can Med Assoc J 1997;156:169-76). Their observations are not surprising, considering that similar wide variations have been observed for other medical procedures. Are these differences due to overutilization in high-rate areas, underutilization in low-rate areas or a combination of these factors? In the editorial "Spirometric testing: How much is enough?" (Can Med Assoc J 1997;156:202-4), Dr. Nicholas Anthonisen suggests that the overall use of spirometry in Ontario is either acceptable or too low. Chan and colleagues suggest, and Anthonisen states, that flow-volume (FV) loops (providing forced vital capacity [FVC], forced expiratory volume in 1 second [FEV"Symbol not transcribed"], forced expiratory flow during the middle half of forced vital capacity [FEF"Symbol not transcribe"] and other data) are being used excessively in comparison with simple spirograms (providing FVC and FEV"Symbol not transcribed"). However, the data presented do not support these conclusions. We do not know whether FV loops were repeated for the same patients during a 1-year period or performed annually, on average. This issue is critical if one accepts Anthonisen's argument that FV loops should not be repeated more than once a year, which is arguable. I cannot reconcile his statement that "it is hard to imagine that as much as half of all-flow studies could justifiably involve flow volume analysis" without any information on the number of studies carried out per patient. In the areas with the highest costs for spirometry, a mean of 5 spirometric tests per 100 population were performed during 1 year. This rate is certainly in line with the rate of asthma (3% to 5%) and of wheezing (up to 9%) in the population.(f.1) The usefulness of FV loops versus simple spirograms is also discussed. The authors agree that spirometry is essential in diagnosis, assessment and follow-up of patients with obstructive lung disease. However, they question whether the FV loop, a powerful tool that provides additional information on small airway obstruction, is being overused. Anthonisen notes that FV loops, which provide information on small airway calibre, may be more sensitive than simple spirograms but that there is a wide range of normal values.