Complete blood count

A complete blood count (CBC) is one of the most common blood tests. It measures the number and characteristics of red blood cells, white blood cells and platelets and helps detect anaemia, signs of infection or inflammation and some blood disorders. It is performed during general health examinations, for symptoms such as fatigue or frequent infections, and to monitor treatment.

Who the test is for

• people having a general or preventive health examination and before surgery;
• people who are persistently tired, weak or pale, have dizziness or become breathless on exertion, when investigating anaemia;
• people with fever, frequent infections or suspected inflammation, often alongside CRP;
• people who bruise easily or frequently bleed from the nose and gums;
• people with chronic conditions and those taking medicines that may affect blood cells, for monitoring.

What a complete blood count shows

A CBC report usually contains these parameters:

Parameter	What it shows
erythrocytes (E)	the number of red blood cells, which carry oxygen
haemoglobin (Hb)	the protein in erythrocytes that binds oxygen; the main indicator of anaemia
haematocrit (Hct)	the proportion of blood volume occupied by erythrocytes
MCV	the average size of erythrocytes
MCH and MCHC	how much haemoglobin is present in an erythrocyte
RDW	how much erythrocytes vary in size
leucocytes (L)	the total number of white blood cells, which defend the body against infections
platelets (Trc)	the number of blood platelets, important for clotting
MPV and PDW	the average platelet size and how much they vary
differential blood count	the proportion of each leucocyte type: neutrophils, lymphocytes, monocytes, eosinophils and basophils

The differential blood count within the CBC is counted by an analyser. When cell appearance needs closer examination, a separate test is performed, the differential blood count (DKS), which is a manual examination of a blood smear under a microscope.

Preparation and sample

CBC uses venous blood. You do not need to fast for a blood count alone, but if glucose, lipids or iron are being measured at the same time, come in the morning fasting. Avoid strenuous exercise the day before and drink enough fluids because exertion and dehydration can temporarily change some values. Tell your doctor which medicines you take.

Blood collection in children is adapted to the child’s age.

How to interpret the result

Reference intervals depend on age, sex and method, and differ from adult intervals for children and pregnant women. They are printed on your report. A value slightly outside the interval is common even in healthy people and does not by itself mean disease. A doctor interprets results alongside your symptoms and previous results.

Red blood cell parameters

Low haemoglobin means anaemia, while MCV helps identify its cause. Small erythrocytes (low MCV and MCH) most often accompany iron deficiency, and less often inherited thalassaemia or anaemia of chronic disease. Large erythrocytes (high MCV) occur with deficiency of vitamin B12 or folic acid, with excessive alcohol consumption, liver disease, an underactive thyroid and some medicines. Raised RDW means erythrocytes vary in size, which is often seen early in iron deficiency. In anaemia, a doctor may also request reticulocytes, which show how many new erythrocytes the bone marrow is producing.

Raised haemoglobin and haematocrit most often result from dehydration or smoking, and less often from bone marrow disease.

Leucocytes

An increased number of leucocytes most often accompanies infection or inflammation, but also rises after exertion, with stress, smoking, during pregnancy and with corticosteroids. A reduced count can occur with viral infections, some medicines and bone marrow disease. The differential blood count shows which leucocyte type has changed, and we discuss inflammation assessment in the article on inflammatory markers.

Platelets

An increased number of platelets is most often a temporary reaction to inflammation, infection, bleeding or iron deficiency. A reduced count may result from a viral infection, medicines, liver disease or immune destruction of platelets. Sometimes the low count is false because platelets clump together after collection, so a doctor requests a repeat test. MPV is interpreted only alongside the platelet count.

CBC, differential blood count and panels

In infections, CBC is often performed together with CRP. For children there is a Children’s panel (CBC, CRP and urinalysis), and for adults a General preventive panel, which includes glucose, blood lipids and liver enzymes alongside CBC. When iron deficiency is suspected, CBC is part of the Ferro (iron) panel.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list.

Frequently asked questions

What is the difference between CBC and DKS?

CBC includes an automated differential blood count showing the proportions of individual leucocyte types. A separate DKS is a manual examination of a blood smear under a microscope, which can reveal immature or abnormal cells. The leucocyte proportions help a doctor assess, for example, whether an infection is more likely bacterial or viral.

Does a blood count show iron deficiency?

Only indirectly. Low MCV and raised RDW may suggest deficiency, but it is confirmed by ferritin. At the start of deficiency, the blood count can be completely normal.

Can a blood count reveal cancer?

CBC is not a test for detecting cancer. Some blood disorders, such as leukaemia, can markedly alter the blood count, while in other diseases the result may show anaemia, for example from hidden bleeding. A normal blood count does not exclude disease, and a mild abnormality most often has a harmless cause.