Blood test is a comprehensive clinical study, during which the qualitative and quantitative composition of blood is determined: erythrocytes (their number, average volume and volume distribution, sedimentation rate), leukocytes (quantity, leukocyte formula), platelets, hemoglobin level are studied. The study has an independent diagnostic value, based on the results, the issue of conducting more in-depth specific tests is being decided. Blood test is prescribed as part of a preventive examination, if there are complaints about the state of health. The list of indications is very wide, includes various diseases accompanied by anemia, polycythemia, thrombocytopenia, thrombocytosis, leukopenia and leukocytosis. Whole blood from veins or capillaries is examined. Preparation of the results takes 1 day.
Blood test is a routine tool for laboratory diagnostics. It is used to detect and monitor many diseases, as well as for preventive examinations in educational and industrial institutions, in the army. The history of this research method has more than 300 years. At the end of the XVII century, Anthony van Leeuwenhoek, a Dutch naturalist, created a microscope and discovered the existence of red blood cells – erythrocytes. He described their shape and size, that is, he conducted the first simplest version of a blood test. Further research followed the path of inventing more accurate methods of quantitative and qualitative study of blood cells. At the end of the XVIII century, Paul Ehrlich mixed aniline dyes and used them to study a blood smear. This allowed him to isolate several types of leukocytes: lymphocytes, mononuclears and granulocytes. The latter were classified as basophils, oxyphils (eosinophils) and neutrophils.
Interest in the study of leukocytes grew, knowledge about their role in infectious diseases deepened. The development of laboratory diagnostics was aimed at improving the methods of coloring and fixing the studied units, their counting and data processing. In the middle of the XX century, Wallace Coulter introduced the first automated analyzer for determining the size and number of blood cells. His invention was called the Coulter counter, it simplified and standardized the scheme of general blood analysis, which made it possible to widely introduce it into clinical practice. In the 70-90s of the XX century, modern automated systems were created for counting leukocytes, erythrocytes and platelets, as well as for differentiating lymphocytes by maturity. In modern clinical and laboratory practice, a blood test combines the use of automatic systems, including the use of flow cytometry, and “manual” microscopic examination, which involves a deeper description of the qualitative characteristics of blood cells.
The full version of the blood test is performed with a leukocyte formula and ESR. The results of the study contain detailed information about the number of different types of blood cells, their structural features. The analysis includes determination of the total number of leukocytes, erythrocytes and platelets, hemoglobin, hematocrit, average volume of erythrocytes, distribution of erythrocytes by volume, erythrocyte sedimentation rate (ESR) and leukocyte formula, in which neutrophils, lymphocytes, monocytes, eosinophils and basophils are represented as a percentage. The results of a blood test are used to diagnose and monitor diseases and conditions accompanied by anemia, polycythemia, thrombocytopenia, thrombocytosis, leukopenia, leukocytosis. The scope of this study is very wide, it is used in almost all areas of medicine: in therapy, pediatrics, surgery, obstetrics, gynecology, etc.
Blood test is prescribed as part of screening examinations, during preventive examinations. It is included in the diagnostic program during hospitalization in hospitals of various profiles. The results allow us to assess the functional state of the body, identify many diseases at the early stages of development, determine the tactics of further research and therapy. In addition, the study is performed for non-specific symptoms, such as fatigue, fatigue, headache and muscle pain, fever. An indication for the analysis may be a suspicion of anemia, an inflammatory or infectious disease, a disease of the blood system, a malignant tumor.
With a certain frequency, a blood test is performed for various chronic diseases in order to monitor them, detect relapses in a timely manner, and evaluate the effectiveness of the treatment. According to the change in indicators, the need for correction of therapy, additional laboratory and instrumental examinations is determined. Blood test is an obligatory part of a comprehensive diagnosis in the pre- and postoperative period, in case of injuries, burns, acute conditions accompanied by fever, shock, dehydration. The results of a laboratory study in combination with clinical data provide the doctor with information about the general condition of the body, the degree of dysfunction of various organs.
Conducting a blood test has no contraindications. However, some conditions and diseases can become an obstacle to the procedure of blood collection. With severe anemia, hypotension, blood clotting disorders, mental and motor arousal, the organization of special conditions for taking the material is required. In modern laboratories, the research procedure is automated, which significantly saves time and labor resources. But analyzers are not always able to take into account the features of the structure and properties of blood cells. For example, in thrombocytopathy with increased platelet aggregation and adhesion, the equipment counts only free units, while the glued ones have the size of red blood cells and can be attributed to them. To correct such errors when performing a blood test, automated examination is often supplemented by “manual” smear microscopy.
Preparation and blood collection
Blood sampling for general analysis is performed in the morning. A day before the procedure, you should refrain from drinking alcohol. The doctor should be warned about all medications taken, if necessary, he will temporarily cancel the drugs or take into account their influence when interpreting the results. It is recommended to make the last meal the night before, that is, 8-12 hours before blood collection. In extreme cases, the interval should be at least 4-6 hours. Drinking clean still water is allowed at any time. In 30 minutes it is necessary to give up smoking, physical and emotional stress.
Most often, blood for a blood test is taken from a finger. The puncture is performed using a scarifier pen or a special disposable device – a lancet. The blood is pipetted into a test tube. A doctor may recommend taking blood from a vein, then the place of taking is the elbow bend, the procedure is performed by puncture with a tourniquet. In most laboratories, the examination procedure is performed using an automatic hematology analyzer. The method of flow cytometry is used to count and measure cells. Its essence lies in the fact that blood cells are passed through the microcapillary system, irradiated with a laser, and the resulting light scattering and fluorescence signals are recorded and processed. In less than a second, the hemanalyzer calculates erythrocyte, leukocyte and platelet indices. After the automatic procedure, the smear is viewed by a doctor under a microscope. The hemoglobin level is determined by colorimetric method (staining), hematocrit is calculated mathematically as the ratio of cells to plasma volume. The results are ready – 1 working day.
Each of the indicators of the blood test has a certain range of norms. It is determined by gender and age:
- The number of leukocytes is 6-17.5 *10^9/l for children, 4-10 *10^9/l for adults.
- The number of red blood cells – 4,1-5,3 *10 ^12/l for children, 3,5-5,2 *10 ^12/l for women, 4,2-5,3 *10 ^12/l for men.
- Platelet count – 99-450 *10^9/l for children, 180-320 *10^9/l for adults.
- Hemoglobin – 110-168 g/l for boys, 110-198 g/l for girls, 126-174 g/l for men, 117-161 g/l for women.
- Hematocrit – 31-55% for children, 35-51% for men, 34-47% for women.
- The average volume of red blood cells is 71-112 fl for children, 81-102 fl for men, 81-102 fl for women.
- The distribution of erythrocytes by volume – 37-45 standard deviation, coefficient of variation of 11.5-14.5 mm.
- ESR – 2-20 mm/h for children 2-20 mm/h for men, 2-30 mm/h for women.
- The number of neutrophils– 1,5-8,5 *10^9/l for children 1,8-7,7 *10^9/l for adults.
- The number of lymphocytes is 2-11 * 10^9/l for children, 1-4.8 m *10^9/l for adults.
- The number of monocytes – 0,05-1,1 *10 ^9/l for children, 0,05-0,82 *10 ^9/l for adults.
- The number of eosinophils – 0,05-0,4 *10 ^9/l for children under 6 years old, 0,02-0,5 *10 ^9/l for children over 6 years old and adults.
- The number of basophils is 0-0.08 *10^9/l for children and adults.
- The proportion of neutrophils is 16-60% for children, 47-72% for adults.
- The proportion of lymphocytes is 30-75% for children, 19-37% for adults.
- The proportion of monocytes is 4-10% for children under 2 years old, 3-12% for children over 2 years old and adults.
- The proportion of eosinophils is 1-7% for children under 4 years old, 1-55 for children over 4 years old and adults.
- The proportion of basophils is 0-1.2% for children and adults.
For a more accurate interpretation of the results of a blood test, it is necessary to take into account the age of the patient, as well as the features of the equipment used in the laboratory. The obtained indicators should be correlated with those indicated in the “reference values” section on the results form. Among the physiological factors, excessive or insufficient nutrition, increased physical activity, and prolonged exposure to stress factors lead to a deviation from the norm. The periods of pregnancy and lactation are also characterized by a slight change in the values of the blood test.
Deviations from the norm
Blood test is the most common study in clinical and laboratory practice. It is performed during preventive examinations, during the primary diagnosis of diseases, during their monitoring, in preparation for operations and after them. The results allow the doctor to assess the general condition of the body, identify disorders in the work of individual organs and systems, make a plan for further examination and treatment. If the indicators deviate from the norm, it is necessary to consult a doctor who sent for analysis. Most often, they are a therapist or pediatrician. To avoid distortion of the results due to the influence of physiological factors, you need to properly prepare for blood donation: perform the procedure on an empty stomach, exclude smoking, emotional and physical exertion.