Rhesus antibodies test – a laboratory study aimed at detecting antibodies in Rh-negative blood to the Rh factor – a specific protein that is located on the surface of red blood cells of Rh–positive blood. The indicator has an independent diagnostic value, the study is carried out after receiving the results of tests to determine the blood group and Rh factor. The data are used to identify the Rh-conflict of the mother and fetus, to determine the need for injections of immunoglobulin to a pregnant woman with Rh-negative blood. The material for the study is venous blood. The titer of antibodies is detected by an agglutination reaction. Normally, with a low probability of Rh conflict, the result is negative. The readiness of the analysis results is 1 working day.
Anti-erythrocyte antibodies are immunoglobulins that are produced to various groups of erythrocyte antigens. These antigens belong to the structural formations of blood cells, located on the outer surface of membranes. By their chemical nature, they are diverse – some are represented by proteins, another by glycoproteins, and the third by glycolipids. Their presence or absence is inherited and does not change during life. The set of antigens does not affect the state of health in any way. If blood with such antigens is transfused into the blood of a person who does not have erythrocyte antigens of a certain type, then the body will produce antibodies – an immune response will develop. Such situations occur after hemotransfusions performed without preliminary analysis for antibodies to the Rh factor, as well as when fetal blood antigens enter the bloodstream of a pregnant woman.
Timely detection of anti-erythrocyte antibodies in the blood is necessary to prevent the development of rhesus conflict, the consequences of which are hemolytic reactions, that is, the destruction of donor red blood cells. During pregnancy, its spontaneous termination at various periods is possible. The study of antibodies to the Rh factor has become the most widespread in obstetric and gynecological practice as a tool for monitoring pregnancies in women with Rh-negative blood. Timely vaccination with anti-D gamma globulin avoids the development of Rh conflict and related complications. In addition, the study of antibodies to the Rh factor is in demand in surgical and resuscitation practice as part of the preparation of patients for blood transfusions. To conduct an analysis for anti-erythrocyte antibodies, blood is taken from a vein. A common method of investigation is the reaction of agglutination on a buffer gel.
Blood test for antibodies is used to prevent extravascular hemolysis after blood transfusions, to prevent the development of fetal erythroblastosis of the fetus. According to the test results, allosensitized patients are identified, the necessary treatment is prescribed. In preparation for pregnancy and its monitoring, the test for antibodies to the Rh factor is performed with a certain frequency. The study is shown to mothers with Rh-negative blood, provided that there is a possibility of transmission of a positive Rh factor from father to child. Especially careful control of anti-erythrocyte antibodies is required for women who have already been immunized previously – had pregnancies with Rh conflict, including those that ended in abortion or miscarriage, or underwent blood transfusions. Also, the risk of developing rhesus conflict is higher in patients with pregnancy complications leading to a violation of the integrity or increased permeability of the placenta. The probability of penetration of fetal erythrocytes increases with placental abruption, abdominal injuries, infections, invasive interventions on the uterus. Based on the results of the analysis, a conclusion is made about the risk of developing rhesus conflict and the need for immunoglobulin injections.
Other indications for performing blood test for antibodies include habitual miscarriage and hemolytic disease of newborns. The results of the study allow us to confirm or refute the role of Rh conflict in the development of pathology. In surgery, intensive care and related fields, an analysis for antibodies to the Rh factor is indicated in preparation for blood transfusions, as well as 15-30 days after the procedures. According to the study, sensitization to antigens and the possibility of blood transfusion of a specific donor are determined.
An anti-erythrocyte antibody test is not indicated if a woman with a negative blood Rh factor is carrying a child whose father also has Rh-negative blood. In these cases, the Rh factor is always negative in the fetus, the immunological conflict does not develop. The results of the study may be positive in the absence of Rh-conflict, if the injection of immunoglobulin was administered to a woman less than 6 months ago. Another limitation of the analysis is its sensitivity – in small concentrations, antibodies cannot be determined. Despite this, the prognostic value of the study is very high – its results allow us to identify the risk of rhesus conflict and prevent its development.
Preparation for analysis and material collection
When performing an analysis for anti-erythrocyte antibodies, the biomaterial is venous blood. The sampling procedure is usually performed in the morning, but there are no strict requirements for the time of its implementation. There is no need to prepare for blood donation. It is recommended to take a break after eating for at least 4 hours, and spend the last 30 minutes before the procedure in a calm environment, without emotional and physical exertion. Blood is taken from the ulnar vein by puncture, placed in a sealed tube and sent to the laboratory within a few hours.
Rhesus antibodies test are determined in the blood by agglutination using a filtration gel. During the procedure, serum with erythrocytes is injected into the upper part of micro-tubes with gel. Then they are incubated and centrifuged. As a result, agglutinated erythrocytes (those that are connected to anti-erythrocyte antibodies) do not pass through the gel due to the increased size and remain on its surface. If there are no antibodies, then red blood cells easily sink through the gel to the bottom of the tube. Thus, the presence of antibodies to the Rh factor is determined by the nature of the distribution of red blood cells. The timing of the analysis is 1 working day.
Normally, the test result for anti-erythrocyte antibodies is negative (-). This means that there are no antibodies in the blood sample under study, and the probability of developing a Rh conflict is low. The final indicator is not influenced by physiological factors, such as physical activity or dietary habits. Incorrect storage and transportation of a blood sample can lead to false results.
In the presence of anti-erythrocyte antibodies in the blood of a pregnant woman, the test result is positive. In this case, their semi-quantitative study is carried out. Depending on the strength of the agglutination reaction in the gel, the result can be strongly positive (++++), positive (+++), weakly positive (++), very weakly positive (+). The reason for the increase in the values of the analysis for anti-erythrocyte antibodies is the sensitization of the body to the Rh factor. It indicates an increased risk of termination of pregnancy, the risk of developing erythroblastosis of the newborn and complications after blood transfusions.
The absence of rhesus antibodies test is the norm and indicates that there is no risk of Rh conflict. If the antibodies were determined earlier, then the reason for the decrease in the values of the analysis is the introduction of anti-D gamma globulin.
Treatment of abnormalities
Analysis for rhesus antibodies test has diagnostic and prognostic value in obstetric and gynecological practice. Its results make it possible to identify the risk of developing an immunological conflict in a pregnant woman with Rh-negative blood and timely administer immunoglobulin. This measure avoids further complications: hemolytic disease of the fetus or newborn, miscarriage, premature birth. With the results of the analysis, you should contact the obstetrician-gynecologist who is leading the pregnancy.