What the three parts tell you
Red cells and haemoglobin carry oxygen — a low level is anaemia, which can cause tiredness and breathlessness and has many possible causes. White cells fight infection — a high count often suggests infection or inflammation, while a low count can increase infection risk.
Platelets help the blood to clot — too few can cause easy bruising or bleeding, and too many can occur with inflammation or other conditions. The test also gives clues (like red-cell size) that help find the cause of anaemia.
What happens with an abnormal result?
Many mild abnormalities are temporary or have a straightforward cause and are simply rechecked. Others lead to further tests — for example iron studies for anaemia — depending on your symptoms and the pattern of results.
Common questions
Does a high white cell count mean a serious illness?
Usually it reflects a common infection or inflammation and settles. Persistently or very abnormal counts are investigated further by your doctor.