PURPOSE: Spirometry is commonly utilized to diagnose obstructive airways defect(OAD). As per spirometric criteria OAD is defined as FEV1/FVC% < LLN based on NHANES III reference equations. However as per ATS/ERS 2005 interpretation strategy, OAD is diagnosed by low FEV1/ best VC ( often SVC). Normally FVC> SVC in many patients with OAD because of dynamic airway collapse resulting in air-trapping and lung hyperinflation. This results in discrepant ratios with normal FEV1/FVC but reduced FEV1/SVC ratio. This results in missed diagnosis of OAD, if only FEV1/FVC is utilized for diagnosis. It is a standard practice to measure only FVC during spirometry. SVC is measured only during static lung volume measurements. To identify the prevalence of missed diagnosis of OAD, based on FEV1/FVC ratio during spirometry when compared to FEV1/ SVC during static lung volume measurements.
METHODS: Retrospective review of PFT data of all patients with clinical diagnosis of asthma and COPD during the time period between 1/09 to 1/11.
RESULTS: Of 497, 81 patients who had normal FEV1/FVC and FEV1/SVC were excluded. Of 416 study patients, 188(45%) were Males and 228 (55%) were Females. The median age was 55 yrs (range,13 to 91 yrs). 185/416 (44%) patients had Asthma and 231/416 (56%) had COPD. In Asthma group normal discordance was seen in 40/185 (22%) patients and in COPD group in 31/231 (13%) patients. Overall the discordance was noted in 71 of 416(17%) patients.
CONCLUSIONS: FEV1/FVC ratio by spirometry was falsely normal in 17% of patient with known OAD; Asthma and COPD. These patients were correctly identified as having obstructive airways disease by low FEV1/SVC.
CLINICAL IMPLICATIONS: FEV1/FVC by spirometry may be spuriously normal in some patients with asthma or COPD. In such patients with a high clinical index of suspicion for OAD, it is advisable to measure static lung volume including SVC and calculate FEV1/SVC ratio. This will help avoid errors in diagnosis and missed therapy.
DISCLOSURE: The following authors have nothing to disclose: Ameer Rasheed, Viswanath Vasudevan, Saleem Shahzad, Farhad Arjomand, Scott Reminick
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