What is the Schamroth sign?

Nail clubbing, also known as digital clubbing or clubbing, is a deformity of the finger or toe nails associated with a number of diseases, mostly of the heart and lungs.

Schamroth's sign or Schamroth's window test (originally demonstrated by South African cardiologist Leo Schamroth on himself) is a popular test for clubbing. When the distal phalanges (bones nearest the fingertips) of corresponding fingers of opposite hands are directly opposed (place fingernails of same finger on opposite hands against each other, nail to nail), a small diamond-shaped "window" is normally apparent between the nailbeds. If this window is obliterated, the test is positive and clubbing is present.