A complete blood count, also called a CBC, full blood count or haemogram, describes several parts of the blood. It can help investigate symptoms and monitor treatment. Reading the groups of results together helps a clinician decide what needs checking next.
Red cells and oxygen transport
Haemoglobin, often abbreviated Hb, is the oxygen-carrying protein in red blood cells. The RBC count measures their number, while haematocrit describes the proportion of blood occupied by them. MCV indicates average red-cell size and can help narrow down possible causes of anaemia.
Low haemoglobin needs an explanation. Iron deficiency is common, but other possibilities include vitamin B12 or folate deficiency, inherited conditions and chronic disease. When iron deficiency is present, finding the reason matters: heavy periods or bleeding from the digestive tract may be involved. A low Hb result alone does not tell you which supplement or treatment is appropriate.
White cells and the immune system
A white-cell count gives the total number of these immune cells. A differential adds information about the individual types. High counts can accompany infection or inflammation and may be affected by medicines. Low counts also have several possible causes, including some infections, medicines and conditions affecting blood-cell production.
The total count cannot identify the cause on its own. Your symptoms, the types of cells affected and changes from earlier tests help guide the next step. If you already know your white-cell count is low and develop a fever or feel unwell, contact your medical team promptly.
Platelets and bleeding
Platelets help form a clot at an injury. Their number and their ability to work properly are different aspects of clotting. Low counts may occur with immune conditions or medicines; higher counts can accompany inflammation, infection or anaemia. A platelet result therefore needs more context than a label saying high or low.
Low platelets do not, by themselves, confirm dengue. When dengue is suspected, clinicians consider symptoms, exposure and appropriate infection tests. Do not use a CBC as a substitute for that assessment.
Prepare for the discussion
Bring the full report and earlier counts. Note recent illnesses, unusual bruising, bleeding, heavy periods, medicines and persistent tiredness. Use your laboratory’s units and reference intervals. Dehydration and other circumstances can influence some measurements, and repeat testing may be useful when the findings need clarification.
Ask which result matters most, whether further tests are needed and how soon you should be reviewed. Seek emergency help for severe breathlessness, chest pain, collapse or uncontrolled heavy bleeding. These symptoms need care without waiting for a new blood count.
References
- MedlinePlus: Complete blood count
- MedlinePlus: White blood count
- MedlinePlus: Platelet tests
- NHS: Iron deficiency anaemia
- MedlinePlus: Dengue fever testing
- NHS: Low white blood cell count
- MedlinePlus: Recognising medical emergencies
- NHLBI: Causes of anaemia
