Blood test


For the doctor it is part of the daily business, for the patient it can bring sweat to the brow: a blood test. It is often a part of the basic programme of medical activity. But why is a blood test carried out so often and on so many different occasions?

What is hidden behind blood tests? When is which blood value determined and what conclusions can the doctor draw from it? The following article is intended to provide some answers to these questions.


The reasons for a blood test can be many and varied. In some cases, blood values are determined in order to make a diagnosis of a disease. Common reasons for diagnostic blood tests are suspected infections, thyroid dysfunction, kidney, liver and metabolic diseases or suspected changes in the blood count, i.e. in the blood cells. Blood tests continue to be carried out during the course of these diseases in order to monitor their development and the response to therapeutic measures. Follow-up examinations are also particularly important when taking certain drugs, the concentration of which in the blood must be kept within narrow limits so that they work, but cause as few serious side effects as possible.

Blood test during pregnancy

Pregnancy represents a special situation for the body, as changes in the most diverse body processes occur. It is therefore not surprising that there can be changes in blood values. For some blood values, deviations from the normal range during pregnancy are known.

The doctor must therefore take these into account when interpreting blood results. Examples include changes in the number of white blood cells, calcium concentration, blood lipids and coagulation values. Certain blood tests can make more sense during pregnancy.

These include examining the blood count to detect a deficiency of red blood pigment (haemoglobin) and red blood cells (erythrocytes). Such a situation, known as anaemia, often occurs during pregnancy due to an iron deficiency. In order to determine this, the so-called ferritin, transferrin and transferrin saturation can also be determined.

The determination of the blood group of the pregnant woman also plays an important role in the preventive medical check-ups during pregnancy, as under certain circumstances problems can arise due to the maternal blood group. As part of the preventive medical check-ups, a standard examination is also performed for type B viral liver inflammation (hepatitis B) in the mother, as this can also infect the child. It is also advisable to have an HIV test done at the latest then, but preferably before pregnancy.

Further tests for pathogens that can cause problems during pregnancy are carried out either routinely or when infection is suspected. This involves testing for antibodies in the mother’s blood. Regular preventive examinations include, for example, testing for immunity to the rubella virus.

For special questions, blood can also be taken from the umbilical cord. In this case, the umbilical cord is punctured through the skin of the pregnant woman under ultrasound control. The blood obtained from the unborn child can then be examined for changes in the chromosomes (in Down syndrome and other genetic disorders), for antibodies in the case of suspected infections, or for suspected anaemia of the child.

Fortunately, this procedure is rarely necessary. In the future, the mother’s blood test will probably also become more important when it comes to detecting genetic disorders in the child. At present, this often requires complex and complication-prone examinations: By testing the mother’s blood alone, the corresponding costly methods could be dispensed with.