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Possible clinical features include:
- the warm mucous membranes are blue, for example the tongue, the inside of the lips
- central cyanosis increases immediately on exercise which is not the case for peripheral cyanosis
- often there is polycythaemia with an abnormally high haemoglobin and haematocrit; this must not be confused with neonatal polycythaemia which may mimic cyanosis
- clubbing is often seen in patients with central cyanosis
Note that the absolute discriminating feature between central and peripheral cyanosis is obtained from testing the oxygen saturation of arterial blood.
In some conditions, particularly Fallot's tetralogy, there may be episodes of paroxysmal hypercyanosis.
Last reviewed 01/2018