PURPOSE: When DLCO is measured at lung volumes below total lung capacity a reduced measurement will be obtained. Some have sought to use DLCO/VA to aid in the interpretation under this circumstance. However, the value of using DLCO/VA when interpretating diffusing capacity measurements remains controversial. In addition, lung diseases that result in a reduced DLCO can be associated with low, normal or high DLCO/VA. We examined the utility of DLCO/VA in the differential diagnosis of a low DLCO in patients with restrictive pulmonary disorders.
METHODS: We performed a retrospective review of data from a university-affiliated hospital pulmonary function laboratory on patients with disorders that cause restriction. Patients were categorized into interstital lung disorders(ILD)[sarcoidosis and other intersitial lung diseases] or extrapulmonary disorders (EPD)[kyphoscoliosis(KS), obesity(OB), and neuromuscular disorders(NMD)]. Sensitivities and specificities for ILD and EPD were calculated for both DLCO and the combination of DLCO and D/VA of various values.
RESULTS: There were 67 patients identified in the ILD group (sarcoidosis,N=36; other,N=31)and 140 patients in the EPD group (OB,N=93; KS,N=26; NMD,N=21). Results for sensitivity and specificity for diagnoses are expressed in the following format: diagnostic test (sensitivity, specificity). For diagnosis of ILD: DLCO≤;50 (38.8%, 90.0%), DLCO≤;50 and D/VA≤;70 (13.4%, 99.0%), DLCO≤;50 and D/VA≤;90 (31.3%, 95.7%); DLCO≤;60 (59%, 82%), DLCO≤;60 and D/VA≤;70 (13.4, 98.5%), DLCO≤;60 and D/VA≤;90 (44.7%, 94.2%). For diagnosis of EPD: DLCO≤;60 (17.8%, 40.0%), DLCO≤;60 and D/VA≥100 (7.8%, 95.5%); DLCO≤;70 (32.1%, 28.3%), DLCO≤;70 and D/VA≥105 (21.0%, 94.0%).
CONCLUSION: In restrictive disorders, a low DLCO is more characteristic of ILD than EPD. The use of DL/VA in addition to DLCO improved the specificity of the test for the differential diagnosis of a low DLCO in this setting. At any level of reduced DLCO, the lower the DLCO/VA the more specific the test was for ILD; the higher the DLCO/VA the more specific the test was for EPD. Specificities in the mid to high 90's were found when DLCO and DLCO/VA were both used.
CLINICAL IMPLICATIONS: D/VA can contribute to the differential diagnosis of a low DLCO in restrictive pulmonary disorders.
DISCLOSURE: Eli Gavi, No Financial Disclosure Information; No Product/Research Disclosure Information