The distance-saturation product predicts mortality in idiopathic pulmonary fibrosis

Christopher J. Lettieri*, Steven D. Nathan, Robert F. Browning, Scott D. Barnett, Shahzad Ahmad, Andrew F. Shorr

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

128 Scopus citations


Introduction: The 6-min walk test (6MWT) has prognostic value in various pulmonary disorders including idiopathic pulmonary fibrosis (IPF). We determined the individual prognostic accuracy of distance walked and oxygen saturation during the 6MWT in patients with IPF. We defined a new composite index, the distance-saturation product (DSP), which is the product of distance walked and lowest oxygen saturation during the 6-min walk test. We compared the performance of the DSP to the individual 6MWT parameters in predicting mortality. Methods: We evaluated pulmonary function tests, 6-min walk parameters and the DSP between survivors and non-survivors. The ability of each measure to discriminate outcomes was determined by receiver operator curves. Results: 81 patients (48 survivors, 33 non-survivors) were included. Pulmonary function tests were similar and did not correlate with survival. Desaturation was greater (89.4% versus 83.7%, P < 0.001) and distance walked was lower (406.9 versus 181.3 m, P = 0.005) in non-survivors. The DSP was significantly lower among non-survivors (364.8 versus 153.5 m%, P < 0.001) and predicted mortality more accurately than either individual 6MWT component (P = 0.035 versus desaturation, P = 0.040 versus distance). A DSP <200 m% was associated with a seven-fold greater risk of 12-month mortality and an 18.0% shorter median survival compared with a DSP>200 m% (P < 0.001). Discussion: Each component of the 6-min walk independently predicted mortality in IPF with greater accuracy than spirometry. However, a composite of both parameters, the DSP, provides slightly greater accuracy and represents a novel measure for assessing survival in patients with IPF.

Original languageEnglish
Pages (from-to)1734-1741
Number of pages8
JournalRespiratory Medicine
Issue number10
StatePublished - Oct 2006
Externally publishedYes


  • 6-min walk test
  • Desaturation
  • Idiopathic pulmonary fibrosis
  • Mortality
  • Pulmonary function tests


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