The diagnosis is made on clinical grounds and confirmed with biochemical tests.

The pattern of thyroid storm is similar to that of thyrotoxicosis: a very suppressed TSH concentration and elevation of unbound T4 and T3. No specific level distinguishes the two. Systemic illness compromises the ability to convert T4 to T3, so T3 levels may only be slightly elevated or normal.

There may also be hyperglycaemia and hypercalcaemia with hepatic enzyme abnormalities.

ECG will often show a tachycardia – arrhythmias may be present with atrial fibrillation being most common. These arrhythmias should be treated in the standard manner. It is important to be aware of the cardiac effects of some thyroid storm treatments e.g. beta-blockers [1].