Associated conditions may be identified by taking a detailed medical history-particular attention is paid to lung, heart, and gastrointestinal conditions-and conducting a thorough clinical examination, which may disclose associated features relevant to the underlying diagnosis. When clubbing is observed, pseudoclubbing should be excluded before making the diagnosis. Schamroths window test, done to identify nail clubbing

PDGF and VEGF have growth promoting properties and cause connective tissue hypertrophy and capillary permeability. They are then trapped within the capillary beds within the extremities, such as the digits, and release platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF). It is thought that in disorders where there is right-to-left shunting or lung malignancy, the megakaryocytes can bypass the breakdown within the pulmonary circulation and enter the systemic circulation. Under normal circumstances in healthy individuals, megakaryocytes that arise from the bone marrow are trapped in the pulmonary capillary bed and broken down before they enter the systemic circulation.

Increased entry of megakaryocytes into the systemic circulation.

Overproduction of prostaglandin E2 by other tissues.

Secretion of growth factors (e.g., platelet-derived growth factor and hepatocyte growth factor) from the lungs.

Vasodilation (i.e., distended blood vessels).

The exact cause for sporadic clubbing is unknown. A congenital form has also been recognized. Therefore, in patients with COPD and significant degrees of clubbing, a search for signs of bronchogenic carcinoma (or other causes of clubbing) might still be indicated. Nail clubbing is not specific to chronic obstructive pulmonary disease (COPD).

Vascular anomalies of the affected arm such as an axillary artery aneurysm (in unilateral clubbing).

Familial and hereditary clubbing and 'pseudoclubbing' (people of African descent often have what appears to be clubbing).

Graves' disease (autoimmune hyperthyroidism) – in this case it is known as thyroid acropachy.

Hepatopulmonary syndrome, a complication of cirrhosis.

Cirrhosis, especially in primary biliary cholangitis.Congenital cyanotic heart disease (most common cardiac cause).Suppurative lung disease: lung abscess, empyema, bronchiectasis, cystic fibrosis.Interstitial lung disease most commonly idiopathic pulmonary fibrosis.Lung cancer, mainly non-small-cell (54% of all cases), not seen frequently in small-cell lung cancer (

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