Why get tested?
If your doctor suspects that you have anaemia (too few red blood cells), polycythaemia (too many red blood cells), or dehydration

When to get tested?
As part of a full blood count (FBC), which may be requested for a variety of reasons

Sample required?
A blood sample drawn from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)