Someone I know has fingernail clubbing should I be worried for them?

I would link them an article. It could also mean they are aware of a serious condition and do not want to let others know about it.

Fingertip clubbing is thought to be caused by increased blood flow to the fingertips. It can run in families and be completely harmless. However, if it suddenly develops, it may be a sign of one of many possible medical conditions, including:

• long-term lung disease or heart disease, such as lung cancer, bronchiectasis, or endocarditis
• inflammatory bowel disease – a long-term condition that causes inflammation of the lining of the gut
• stomach cancer or bowel cancer
• cirrhosis (scarring of the liver)
• polycythaemia – a condition where the blood is too thick

I would definitely advise getting it checked out by a doctor if only to rule out these possibilities.

From what I understand more than half of people with this condition have no medical issues at all. If it’s a recent development I would be finding out if there is a cause or not.

You have expressed your concern to the person. There is nothing more for you to do – unless they bring it up.

@Ltryptophan Clubbing does not happen overnight. Long standing lung and or heart disease are probable cause.