What of the following should prompt for an HRCT?

Presence of obstructive functional pattern

Presence of reduced DLCO

Presence of velcro crackles

Presence of digital clubbing

Author’s solution

The presence of the characteristic velcro crackles should always raise suspicion for an underlying fibrotic lung disease.
The presence of digital clubbing (although a characteristic of fibrotic lung disease) in a smoker imperatively renders the exclusion of an underlying malignancy.

Cottin V & Cordier J. Eur Respir J 2012;40:519–521.