• An electrocardiogram should already have been done to confirm the diagnosis of atrial fibrillation. An electrocardiogram may also indicate a possible underlying cause (such as an old myocardial infarction, left ventricular hypertrophy, or a pre-excitation syndrome).
• Do the following tests:
• Thyroid function tests (to exclude hyperthyroidism).
• Full blood count (to exclude anaemia).
• Blood urea and electrolytes, calcium, and glucose measurement (to exclude electrolyte disturbances, which may precipitate atrial fibrillation).
• Liver function tests and clotting screen (to assess suitability for warfarin).
• Chest radiography (to assess a suspected lung abnormality, such as lung cancer; this test may also help to detect heart failure).
• For people not being referred to a cardiologist, consider organizing transthoracic echocardiography if:
• There is a high risk or a suspicion of underlying heart disease (for example signs of heart failure or a cardiac murmur).
• Information on cardiac structure or function is needed to make a decision about starting antithrombotic treatment.
• Most decisions about starting antithrombotic treatment should be based on clinical judgement. Do not routinely organize echocardiography solely for risk stratification if the person meets the clinical criteria to start warfarin.

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