What diagnostic tests should be done after discovering clubbing in a patient without cardiopulmonary symptoms?

Views of the patient’s fingers and fingernails. (A) Superior view of early clubbing. (B) Profile view of early clubbing. (C) The depth at the nail fold is greater than the depth at the distal interphalangeal joint (DIP), which confirms the presence of clubbing. Point D (the hyponychium) is lower than the extension of line AB created from the DIP joint to the nail fold. This angle ABD (hyponychial angle) is greater than 180 degrees, also confirming clubbing. The profile angle (or the Lovibond angle) is visually the hardest to estimate. This angle, formed by ABC, is also greater than 180 degrees, which would prevent a diamond-shaped window from appearing when this digit is opposed nail-to-nail with the corresponding digit on the opposite hand with angle ABC greater than 180 degrees (Schamroth sign).