Clubbing of the fingers or toes is defined by which nail bed change?

• A. Fingers or toes become enlarged due to acute hypoxia
• B. Loss of mobility occurs in the finger or toes due to hypercarbia
• C. The angle of the nail bed is increased
• D. Polycythemia due to heart disease is also present

Answer: (C)

Clubbing is defined by a change in the nail bed where the angle between the nail plate and the nail bed becomes more obtuse. In a normal finger, this angle is around 160 degrees; in clubbing, the angle increases, giving the distal nail bed a rounded, curved appearance and the fingertips a bulbous look. This nail-bed change reflects chronic changes at the distal digit often linked to long-standing hypoxia from heart or lung disease, among other causes. The other statements don’t describe the defining nail-bed feature: clubbing isn’t characterized by acute hypoxia causing enlargement, loss of mobility from hypercarbia, or a specific polycythemia finding—those are different issues, not the nail-bed angle change that defines clubbing.