Nail clubbing is a relatively specific issue. It often has no clinical significance, but on the other hand in some cases it is present in a number of serious diseases of cardiovascular system.
Nail clubbing occurs due to vascular changes of small arteries in fingers, but precise mechanism of this condition is not known. These changes can occur in number of diseases associated with poor blood oxygenation such as congenital heart defects (like Tetralogy of Fallot), lung diseases (COPD, pulmonary fibrosis, tuberculosis, bronchiectasis, etc.). Clubbing accompanies liver diseases, typically liver cirrhosis. However, as stated above, nail clubbing can be also totally benign finding without any serious cause.
Clubbing develops because of extension of and enlargement of distal phalanges that begin to look like drumsticks. This is usually accompanied by nails deformation into shape of watch-glasses.
Schamroth’s test - Attach two corresponding fingers by their nails. There is free space at healthy
fingers between them called Schamroth’s window. There is no free space at clubbing fingers.
Clubbing of fingers is easily visible by naked eye. When there is strong suspicion on this symptom, it is wise to ate least basically check the status and function of liver, lung and heart. An interesting and easy way to diagnose nail clubbing is so-called Schamroth’s test (Schamroth’s sign).