Controversies in spirometry
CMAJ 1997;157:366
See response from: B. Chan, G. Anderson & R. Dales
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," CMAJ 1997;156:169-76 [abstract / résumé]). 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?" (CMAJ 1997;156:202-4 [abstract / résumé]), 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 flowvolume (FV) loops (providing forced vital capacity [FVC], forced expiratory volume in 1 second [FEV1], forced expiratory flow during the middle half of forced vital capacity [FEF25%-75%] and other data) are being used excessively in comparison with simple spirograms (providing FVC and FEV1). 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.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. Small airway obstruction, as measured by changes in FEF25%-75%, may be seen in asthma and smokers before any changes in FEV1, which measures air flow in larger airways.24 The FEF25%-75% may be abnormal when the FEV1 is normal. In this case, monitoring asthma with the use of simple spirograms may not provide necessary information. I doubt that many, if any, respirologists use simple spirometry rather than FV loops either in office settings or hospital laboratories.
The wide variation in normal values for FEF25%-75% can be taken into account through the use of well-recognized standardized reference ranges for FEF25%-75%5 and of FV loops to follow changes in small airway obstruction in response to treatment.
However, we must ensure that any tests are done for the benefit of the patient and not for purely economic reasons, especially if physicians with no special training in the area are performing high volumes of tests despite easy access to specialists. Such deviations in practice patterns are monitored by provincial health insurance plans, however, and physicians involved may be subject to audit.
Antony J. Ham Pong, MB, BS
Ottawa, Ont.
References
- Cookson JB. Prevalence rates of asthma in developing countries and their comparison with those in Europe and North America. Chest 1987;91(6 suppl):97S-103S.
- Guidelines for the diagnosis and management of asthma. National Heart, Lung, and Blood Institute. Expert Panel Report J Allergy Clin Immunol 1991;88(3 pt 2):425-534.
- Cropp GA. Testing and lung function in office practice. In: Settipane GA, editor. Current treatment of ambulatory asthma. N Engl Reg Allergy Proc 1986;7:19-30.
- De Boeck C, Zinman R, Larson C, Fox Z. Importance of physician identification of airflow limitation in stable asthmatics. Ann Allergy 1984;53:30-4.
- Hsu KH, Jenkins DE, Hsi BP, Bourhofer E, Thompson V, Hsu FC, et al. Ventilatory functions of normal children and young adults -- MexicanAmerican, white and black. I. Spirometry. J Pediatr 1979;95:14-23.
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