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General blood test
Last reviewed: 04.07.2025
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General clinical examination is one of the most important diagnostic methods, subtly reflecting the reaction of hematopoietic organs to the impact of various physiological and pathological factors. In many cases, it is of great importance in making a diagnosis, and in diseases of the hematopoietic system, it plays a leading role.
The term "general clinical blood test" (general blood analysis) includes determination of hemoglobin concentration, red blood cell count, color index, white blood cells, erythrocyte sedimentation rate (ESR) and white blood cell count. If necessary, blood clotting time, bleeding duration, reticulocyte and platelet counts are additionally determined. Currently, most indicators are determined on automatic hematology analyzers, which allow simultaneous examination of 5 to 36 parameters, the main ones of which include hemoglobin concentration, hematocrit, red blood cell count, MCV, mean red blood cell hemoglobin concentration, mean red blood cell hemoglobin content, red blood cell size distribution half-width, platelet count, mean platelet volume, and white blood cell count.
[ Preparation for a general blood test
For clinical analysis, capillary blood is used, which is obtained from a finger (usually the ring finger, less often the middle and index finger) by puncturing the lateral surface of the soft tissues of the terminal phalanx with a special disposable lancet. This procedure is usually performed by a laboratory technician.
Before taking blood, the skin is treated with a 70% alcohol solution, the first drop of blood is blotted with a cotton ball, and subsequent drops are used to prepare blood smears, collected in a special glass capillary to determine the erythrocyte sedimentation rate, as well as to evaluate other indicators, which will be discussed below.
Basic rules for taking blood from a finger
To avoid mistakes when performing a clinical blood test, you need to follow some rules. A finger prick blood test should be taken in the morning after an overnight fast, i.e. 8-12 hours after the last meal. The exception is when the doctor suspects the development of a serious acute disease, such as acute appendicitis, pancreatitis, myocardial infarction, etc. In such situations, blood is taken regardless of the time of day or meal.
Before visiting the laboratory, moderate drinking of water is allowed. If you drank alcohol the day before, it is better to give blood for analysis no earlier than 2-3 days later.
In addition, before taking blood for testing, it is advisable to avoid excessive physical activity (cross-country running, lifting weights, etc.) or other intense impacts on the body (visiting a steam room, sauna, swimming in cold water, etc.). In other words, the physical activity regime before donating blood should be the most normal.
You should not knead or rub your fingers before taking blood, as this can lead to an increase in the level of leukocytes in the blood, as well as a change in the ratio of liquid and dense parts of the blood.
The main indicators of a clinical blood test and what their changes may indicate
The most important indicators for assessing the health status of the subject are the ratio of the volume of liquid and cellular parts of the blood, the number of cellular elements in the blood and the leukocyte formula, as well as the content of hemoglobin in erythrocytes and the erythrocyte sedimentation rate.