The JAMA Rational Clinical Examination recommends two clinical signs:
The Lovibond angle (angle between proximal nail bed and nail plate) CLUBBING: >180° (normal is 160° or less)
Distal phalangeal finger depth (DPD) to Interphalangeal finger depth (IPD) ratio. CLUBBING: DPD > IPD (normal is IPD > DPD)
NOTE: The Schamroth’s sign (Obliteration of diamond-shaped window between the dorsum of terminal phalanges) is typically taught during bedside rounds but the precision and accuracy of this sign have not been formally tested.
Lampe RM, Kagan A. Detection of clubbing—Schamroth’s sign. Clin Pediatr (Phila). 1983;22(2):125.
Myers KA, Farquhar DR. Does This Patient Have Clubbing?. JAMA. 2001;286(3):341-347. doi:10.1001/jama.286.3.341
Validity and Reliability of the Schamroth Sign for the Diagnosis of Clubbing. JAMA. 2010;304(2):159-161. doi:10.1001/jama.2010.935