Complete blood count

and Eva Rudolf-Müller, doctor

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

More about the experts All content is checked by medical journalists.

A complete blood count includes the determination of other cell types in addition to the laboratory values of the small blood count. These are primarily the different types of cells in the white blood cells, called leukocytes. The complete blood count is mainly done if an acute or chronic infectious disease is suspected. Read here what blood values a complete blood count contains, what they tell you and whether you have to appear sober for a complete blood count.

What is a complete blood count?

A complete blood count includes all laboratory values that are recorded for the small blood count, as well as a few additional parameters. The common laboratory values are:

red blood cells (erythrocytes)
red blood pigment (hemoglobin, Hb level)
Percentage of cells in the blood (hematocrit)
mean cell volume of a red blood cell (mean cellular volume, MCV)
mean concentration of hemoglobin in a single red blood cell (mean corpuscular hemoglobin, MCH)
mean concentration of hemoglobin in all red blood cells (mean corpuscular haemoglobin concentration, MCHC)
white blood cells (leukocytes)
Blood platelets (thrombocytes)

In addition, the different types of leukocytes are examined more closely for a complete blood count. These are:

rod-like and segmented granulocytes (neutrophilic granulocytes)
eosinophils and basophils
Monocytes
Lymphocytes

They are determined quantitatively. This means that you determine their percentage in the blood. The doctor also examines the nature of the cells, i.e. their morphology. The determination of the types of leukocytes is also called differential blood count. A complete blood count thus combines a small blood count and a differential blood count.

When do you do a complete blood count?

The small blood count is carried out as part of many routine tests. The values contained therein can provide indications of anemia or impaired blood formation. The additional determination of the various leukocytes, so that a complete blood count results from them, is mainly carried out if infections are suspected.

Complete blood count: sober or not?

In order to be able to assess some blood values, the patient has to appear on an empty stomach for a blood sample. This applies, for example, to parameters of the sugar and fat metabolism. Fasting means that it is best for the patient not to drink anything from the previous evening at 8 p.m. (apart from sugar-free drinks such as water or unsweetened tea).

Complete blood count: values in the normal range

A complete blood count is done from a venous blood sample. The following table provides an overview of the normal values for a healthy adult. Different reference values apply to children depending on their age.

Measurand	Normal value (men)	Normal value (women)
Leukocytes	4,000-10,000 / µl
Erythrocytes	4.8 - 5.9 million / µl	4.3 - 5.2 million / µl
hemoglobin	14 - 18 g / dl	12 - 16 g / dl
Hematocrit	40 – 54 %	37 – 47 %
MCV	78-94 fl
MCH	28 - 34 pg
MCHC	30 - 36 g / dl
Platelets	150,000 - 400,000 / µl
Rod-like granulocytes	3 – 5 %
Segmented granulocytes	50 – 70 %
Basophils	0 – 1 %
Eosinophils	1 – 4 %
Monocytes	3 – 7 %
Lymphocytes	25 – 45 %

While the doctor used to have to count the individual cells under the microscope, the quantitative determination of laboratory values is now done exclusively with special automatic counters.

When are the values in the large blood count changed?

A blood count is not only used to diagnose diseases of the blood itself: diseases of various organs such as the liver or kidneys can also lead to a changed composition of the blood components. The different cell types in the differential blood count react differently to diseases.

Complete blood count: white blood cell count

If the leukocyte count is too high (> 10,000 / µl), one speaks of leukocytosis. It arises, for example, in infections, whereby a bacterial infection increases the number of leukocytes more clearly than a viral disease. Other causes of leukocytosis are:

Inflammation
emotional stress
Allergies
Poisoning
Taking certain medications (such as corticosteroids)
advanced cancers
Metabolic disorders (for example, gout or diabetic coma)
Shock states
trauma
Leukemias, especially chronic myeloid leukemia (CML)

A low white blood cell count is called leukopenia. For example, it is the result of cell-damaging drugs (chemotherapy), bone marrow damage or virus infections. In addition, some diseases lead to leukopenia due to an increased breakdown of leukocytes.

Complete blood count: neutrophils

Complete blood count: eosinophils

Complete blood count: basophils

An increased proportion of basophilic granulocytes (basophilia) is rare. Slight increases occur with elevated blood lipid levels, such as those in the context of diabetes mellitus. Otherwise, basophilia occurs in chronic myeloproliferative diseases - diseases in which the bone marrow produces too many cells. Examples are CML, idiopathic myelofibrosis and polycythemia vera.

A reduction in basophilic granulocytes (basopenia), on the other hand, like eosinopenia, has no significance.

Complete blood count: monocytes

Complete blood count: lymphocytes

What to do if the large blood count changes?

If a complete blood count shows a change in individual values, the doctor must determine the underlying cause - unless the available laboratory values already indicate this. If the differential blood count is elevated, it is particularly important to clarify leukemia or other malignant diseases. However, a complete blood count alone is usually not enough to make an accurate diagnosis.

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