Don't panic when you encounter a patient with Rh-negative blood

This is the 4556th article of Da Yi Xiao Hu

Another ambulance came roaring in, bringing a young male patient injured in a car accident. The medical staff in the emergency room treated him in an orderly manner. At this time, the phone rang. After answering the phone, Dr. Xiao Zhao said to Director Wang anxiously: "Director, this patient has Rh-negative blood!" "Don't worry, continue to rescue." Director Wang said calmly.

Why does Rh-negative blood make Dr. Zhao anxious? Let's first understand Rh blood type. There are many inherited antigens composed of glycoproteins and sugar chains on the surface of red blood cells, which determine a person's blood type. At present, more than 30 types of human blood types have been discovered, among which ABO and Rh blood types are the two most important. Other blood types are not so important in clinical practice because they are not very antigenic.

The Rh blood type is relatively complex, with six antigens: C, c, D, d, E, and e. Among them, D has the strongest antigenicity and is the culprit that causes hemolysis. When the D antigen is present on red blood cells, it is called Rh positive blood, and vice versa, it is Rh negative blood. People of different races have different proportions of Rh negative blood. For example, it accounts for as high as 15% among Caucasians. The Rh negative proportion in the Miao ethnic group in my country is also relatively high, reaching 13%, and the proportion among the Uyghurs is 5%. However, it only accounts for 0.3% among the Han people, especially those with Rh negative AB blood type, which accounts for less than 0.03%. Therefore, during trauma emergency treatment, when encountering Rh negative patients who need blood transfusions, it is very difficult to find blood products of the same blood type, which is also the reason why Dr. Xiao Zhao is anxious.

Unlike ABO blood types, there are no natural anti-D antibodies in the human body, which means that people with Rh-negative blood will not have a transfusion reaction when they receive Rh-positive blood for the first time. But what's worse is that after a person with Rh-negative blood receives a transfusion of Rh-positive red blood cells, there is a 50% chance that they will produce anti-D antibodies two weeks later, and they may not be able to receive Rh-positive blood next time.

In emergency treatment, for patients with Rh-negative blood, the first choice is of course to transfuse blood with the same Rh and ABO blood types. However, when the same type of blood cannot be obtained and life-saving measures are necessary, we must also know that it is safe for Rh-negative patients to receive Rh-positive blood for the first time, and no transfusion reaction will occur. We must not mechanically wait for the same type of blood and delay life-saving measures. In this case, we must immediately ask the patient and his relatives whether they have received Rh-positive blood before. Even if they have received Rh-positive blood before, it does not mean that they cannot receive it again, but a cross-matching test is needed to rule out the possibility that the patient has produced anti-D antibodies.

If the patient is a female Rh-negative, in addition to asking whether the patient has ever received a blood transfusion, we should also ask whether she has a history of pregnancy and miscarriage. Because when an Rh-negative woman is pregnant with an Rh-positive fetus, a small amount of the fetal red blood cells can enter the mother's body, inducing the mother's blood to produce anti-D antibodies. After that, the patient may have a serious transfusion reaction when transfused with Rh-positive blood. Rh-negative is a recessive gene. If the partner of an Rh-negative woman is Rh-positive, the fetus she is carrying may be Rh-negative or Rh-positive. For women who want to have children in the future, even if they are sure that there are no anti-D antibodies in their bodies, they should try not to receive Rh-positive blood transfusions, otherwise future pregnancies may cause neonatal hemolytic disease.

In emergency treatment, in addition to transfusing red blood cells, plasma and platelet transfusions are often required. Let’s talk about plasma first. Since there are no anti-D antibodies in the plasma of Rh-positive blood donors, it is safe to transfuse Rh-positive plasma to Rh-negative patients, and it will not induce Rh-negative patients to produce anti-D antibodies, which will affect future blood transfusions. Would it be safer if Rh-negative plasma could be transfused? That may not be the case. If the Rh-negative blood donor has anti-D antibodies in his plasma because he has received Rh-positive blood before, and the Rh-negative patient is forced to receive Rh-positive red blood cells at the same time, a transfusion reaction may occur. This is indeed a bit confusing, but fortunately this is only a special case. Most of the time, transfusing plasma and cryoprecipitate to Rh-negative patients only requires ABO blood type matching.

Sometimes, platelet transfusion is required in emergency situations. Rh-positive blood donors do not contain D antigens on their platelets, and there is no D antibody in their plasma. Is it always safe to transfuse them to Rh-negative patients? Not necessarily. It depends on whether it is concentrated platelets or single-donor platelets. Concentrated platelets are separated and prepared from multiple donated whole blood, which may be mixed with a small amount of red blood cells and white blood cells. The incidence of transfusion reactions is high, and it may induce Rh-negative patients to produce anti-D antibodies. Generally speaking, the transfusion of concentrated platelets requires that both the ABO blood type and the Rh blood type must be compatible; single-donor platelets are collected from the blood of a donor using a separation machine. They are of high purity, and the number of platelets is more than 12 times higher than that of concentrated platelets obtained from 200 ml of whole blood. The amount of red blood cells and white blood cells mixed in them is very small. As long as the ABO blood type matches that of the Rh-negative patient, it is still relatively safe even if the Rh blood type is different. However, to be on the safe side, the "Recommended Protocol for Emergency Blood Transfusion in Special Situations" recommended by the Blood Transfusion Physicians Branch of the Chinese Medical Association and the Clinical Blood Transfusion Branch of the Chinese Medical Association recommends that for Rh-negative women or girls of childbearing age without anti-D antibodies, after transfusion of RhD-positive single-donor platelets, those who have the conditions should be injected with anti-D human immunoglobulin as soon as possible to prevent antibody production.

Although so many methods have been mentioned, blood transfusion for RhD negative patients is still a thorny issue. If it is necessary for elective surgery, autologous blood transfusion may be carried out. If it is an emergency rescue, it is necessary to try to find the same type of blood for transfusion. Therefore, the government and some non-governmental organizations have established mutual aid groups for Rh negative rare blood types, which can lend a helping hand when Rh negative patients need blood urgently.

The Zhejiang University research team "covered" the surface of red blood cells with a three-dimensional gel network, making it impossible for antibodies to recognize the D antigen, thereby "disguising" Rh-positive red blood cells as Rh-negative red blood cells. I believe that in the future, scientific research and the use of drugs will solve the blood transfusion problem of Rh-negative patients. At that time, we may no longer have to search for "panda blood".

Author: Songjiang Hospital Affiliated to Shanghai Jiaotong University School of Medicine

Emergency Critical Care Department Wang Xuemin

Some pictures are taken from the Internet. If there is any infringement, please let us know and they will be deleted.

All names and place names are pseudonyms and any similarity is purely coincidental.