(Correcting) misdiagnoses of asthma: a cost effectiveness analysis

Abstract

Background: The prevalence of physician-diagnosed-asthma has risen over the past three decades and misdiagnosis of asthma is potentially common.

Objective: to determine whether a secondary-screening-program to establish a correct diagnosis of asthma in those who report a physician diagnosis of asthma is cost effective.

Method: Randomly selected physician-diagnosed-asthmatic subjects from 8 Canadian cities were studied with an extensive diagnostic algorithm to rule-in, or rule-out, a correct diagnosis of asthma. Subjects in whom the diagnosis of asthma was excluded were followed up for 6-months and data on asthma medications and heath care utilization was obtained. Economic analysis was performed to estimate the incremental lifetime costs associated with secondary screening of previously diagnosed asthmatic subjects. Analysis was from the perspective of the Canadian healthcare system and is reported in Canadian dollars.

Results: Of 540 randomly selected patients with physician diagnosed asthma 150 (28%; 95%CI 19-37%) did not have asthma when objectively studied. 71% of these misdiagnosed patients were on some asthma medications. Incorporating the incremental cost of secondary-screening for the diagnosis of asthma, we found that the average cost savings per 100 individuals screened was $35,141 (95%CI $4,588-$69,278).

Conclusion: Cost savings primarily resulted from lifetime costs of medication use averted in those who had been misdiagnosed.

Figure 1

Serial asthma testing algorithm (Confirmed Asthma = 346, Asthma excluded = 150) (PC₂₀ - the provocation concentration that caused decrease in forced expiratory volume in 1 second (FEV₁) of 20%).

Figure 2

Years since diagnosis of asthma and probability of being on asthma medication.

Figure 3

Discounted lifetime cost of asthma medication by years since diagnosis for the subjects where diagnosis of asthma was ruled out by diagnostic algorithm.