RH factor blood test is a comprehensive laboratory study aimed at determining the individual antigenic characteristics of erythrocytes and the presence or absence of Rh antigen on their surface. The diagnostic procedure is prescribed to assess the compatibility of donor and recipient blood before transfusion, surgery, organ and tissue transplantation, as well as to determine the presence of Rh conflict or the risk of its development during pregnancy planning and management. The material is venous blood. The method of investigation is the agglutination reaction. According to the results of the analysis, blood belonging to one and four groups (0, A, B, AB) and the presence or absence of Rh factor (Rh+, Rh-) are determined. The preparation of the results takes no more than 1 working day.
RH factor blood test determine the presence or absence of antigens of a certain type on erythrocytes, which makes it possible to establish blood compatibility between donor and recipient, mother and fetus. The history of these studies begins in 1899, when the Belgian immunologist and bacteriologist J. Borde was the first to determine that in vitro antibodies to erythrocytes in the presence of complement cause agglutination of red blood cells and/or hemolysis. Since 1901 , American doctors K. Landsteiner and F. Levin studied the features of red blood cells, including those isolated from animal blood, and discovered the existence of blood groups. In 1928-1929, their studies were formalized, the Hygienic League of Nations approved the now accepted division of blood groups – 0 (I), A (II), B (III) and AB (IV). This discovery has led to the spread of blood transfusion procedures in clinical practice, as it has become safer. In 1940, K. Landsteiner and A. Wiener discovered the existence of the Rh factor, determined its role in the development of fetal erythroblastosis and complications after blood transfusions.
To date, tests for blood type and Rh factor are basic isoserological studies. They are used in surgery, transplantology, intensive care, hematology, obstetrics and gynecology. During the analysis, a set of antigens present on the surface of red blood cells is determined. These antigens are diverse in their chemical structure, currently several dozen of them have been isolated. The most studied and significant in clinical practice are antigens A and B, which determine the blood group, as well as antigen D, which determines the Rh factor. Blood type and Rh factor are inherited traits, they do not change during life.
The study of the blood group and Rh factor is relevant in situations where blood transfusion is necessary, as well as during pregnancy, when there is a possibility of fetal red blood cells entering the mother’s bloodstream. This is due to the fact that in the absence of any antigen in the blood of the recipient (or mother), the introduction of this antigen with the erythrocytes of the donor (or fetus) leads to the production of antibodies. They destroy foreign red blood cells, provoke the development of an immunological conflict according to the ABO system or the Rh factor system. With blood transfusions, this complication is manifested by hemolytic reactions of varying severity. If an immunological conflict has developed during pregnancy, then the risk of its spontaneous termination, the development of hemolytic disease of the fetus (newborn) increases.
One of the most common indications for blood type and Rh factor analysis is blood transfusion. The study is carried out in preparation for this procedure in order to establish the compatibility of the blood of recipients and donors. The analysis is often performed in situations where there is a high probability that hemotransfusion will be required – during operations and invasive diagnostic interventions, during service in the armed forces and other structures where injuries and injuries are possible. Information about the blood group and Rh factor is entered into medical and other documentation, in a critical situation, it allows you to quickly pick up the blood of a donor.
Determination of blood type and Rh factor is indicated for pregnant women. The study is prescribed during pregnancy planning and monitoring to prevent the development of conflict in the ABO system and in the Rhesus system. Group conflict most often occurs in women with blood type I in couples where the future father has group II, III or IV. It manifests itself as a hemolytic disease of the newborn, which has signs of jaundice and proceeds relatively easily. Rhesus conflict can develop in women with a negative Rh factor if the future father has Rh-positive blood. This complication is more dangerous than a group immunological conflict, can lead to spontaneous termination of pregnancy, damage to some fetal organs, hemolytic disease of the fetus and newborn. The risk group for the development of immunological conflicts of both types includes women who have complications with increased placental permeability – with placental abruption, who have suffered serious infections, abdominal injuries, invasive diagnostic procedures on the uterus. In all these cases, there is a high risk of penetration of fetal erythrocytes into the mother’s bloodstream, followed by the production of antibodies.
Preparation and blood collection
Blood is taken from a vein to determine the group and Rh factor. The sampling procedure in most laboratories is performed in the morning. There are no strict training requirements. It is recommended to refrain from eating fatty foods a day before the analysis, donate blood at least 4 hours after eating. Some medications enhance the agglutination reaction and therefore can lead to false positive results when determining the Rh factor. The need to cancel medications should be discussed with a doctor a few days before the study. For half an hour it is worth abstaining from smoking, physical and emotional stress. Blood is taken from the ulnar vein by puncture.
In the laboratory, studies are carried out using methods based on the agglutination reaction. Blood group determination is performed in three main ways: using isohemagglutin sera, using isohemagglutin sera and standard blood cells, as well as the method with anti-A and anti-B coliclones. The most common is the first option. Standard isohemagglutine serums of groups I, II and III are applied to a special plate in two series – only 6 drops. The test blood (or red blood cells) is added to each and carefully mixed. After 5 minutes, the result is evaluated by the presence of an agglutination reaction in the droplets, that is, by the formation of flakes. If there is no agglutination – the first blood type, coagulation in all samples except II in both series – the second, coagulation in all samples except III in both series – the third, agglutination in all samples – the fourth.
In clinical and laboratory conditions, the determination of the Rh factor is performed by agglutination in a salt medium, by conglutination using gelatin, using an indirect Coombs test, reaction with anti-D-monoclonal antibodies. Salt agglutination is a common diagnostic test. The patient’s erythrocytes are injected into an isotonic sodium chloride solution, mixed and placed in a test tube with antiresus serum. Within one hour, the biomaterial is incubated, after which the formed precipitate is examined. If it has a filamentous and granular pattern, then the Rh factor is positive, if the sediment is evenly distributed along the bottom of the tube, it is negative. The determination of the Rh factor and blood group is performed within 1 working day.
The results of the RH factor blood test contain information about the blood type and Rh factor. Belonging to a certain blood group is established according to the generally accepted ABO system:
- if agglutinogens A and B are not detected on the erythrocyte membrane, then group 0 (I);
- if agglutinogen A is detected, then group A (II);
- if agglutinogen B is detected, then group B (III);
- if agglutinogens A and B are detected, then group AB (IV).
Depending on whether agglutinogen D is present on the outer side of the erythrocyte membranes, a conclusion is made about the Rh factor. There may be two options: the antigen is detected – Rh-positive blood (Rh+), not detected – Rh-negative (Rh-).
The results of these studies are taken into account during blood transfusions and when determining the risk of an immunological conflict between a pregnant woman and a fetus. Universal donors are considered to be persons with the first blood group and a negative Rh factor – 0 (I) Rh-, since they lack all three types of antigens and, therefore, the production of antibodies from the donor will not occur. Universal recipients are persons with a fourth blood group and a positive Rh factor – AB (IV) Rh+. All three types of antigens are present on the erythrocytes of their blood, which means that if any of them get together with the donor’s erythrocytes, the production of antibodies will not be started.
The significance of the RH factor blood test
RH factor blood test are basic isoserological studies. They are used in preparing patients for blood transfusions, for surgical operations, in planning and monitoring pregnancy. Blood typing is necessary for persons entering military service and other law enforcement agencies. Taking into account the blood group and Rh factor during blood transfusions and pregnancy monitoring allows you to prevent the development of immunological conflicts according to the ABO system and the Rh factor system, to avoid the occurrence of severe complications, such as acute hemolytic reaction, hemolytic disease of the newborn, miscarriage. When performing tests in the planned mode, it is necessary to contact the attending general practitioner, obstetrician–gynecologist with the results so that the data can be entered into medical documents and can be used in the future.