A blood test is a general name for all tests that are done in blood, tapped from the patient. Which values have to be determined in the blood test, depends on what the doctor wants to know. The most common analyses in a blood test are sedimentation rate, blood gases and hemoglobin concentration.


Blood tests are performed in order to detect diseases, to determine the severity of a disease, to monitor chronic diseases or to evaluate the effect of a treatment.


The blood sample is analyzed in the laboratory and compared with a number of standard blood values. This means that there is investigated whether elements in the blood fall within defined limits. If this is not the case, we speak of abnormal blood values. The patient then has a shortage or a surplus of certain substances. The doctor can make a preliminary diagnosis on the basis of these values.


In order to tap blood, the nurse tightens a tourniquet around the upper arm, allowing the veins in the forearm to swell and be better visible. A vein is punctured and a small amount of blood flows through the needle into one or more tubes. The number of tubes depends on the number of tests that has to be done. If the tubes are filled, the nurse takes the needle out of the arm and sticks a patch to it. For some types of blood test, the patient must have been fasting.
A blood test is a relatively simple examination that takes little time. The result is known within days, often the next day.