Is it reliable to determine parent-child relationship based on blood type? Why is it so difficult to determine parent-child relationship based on blood type?

Audit expert: Jin Tao

Chief Physician of Hematology Department, Shenyang Red Cross Hospital

In early February, Shaanxi Blood Station discovered a case of CisAB blood type . Compared with Rh-negative blood, which is called "panda blood", CisAB blood type is rarer and is called "golden blood". CisAB blood type, also known as cis AB type, is a rare type of AB blood. Its frequency in the population is between 1 in 580,000 and 1 in 170,000, which is hundreds of times rarer than Rh-negative blood, commonly known as panda blood.

In fact, the ABO type we are familiar with is only one of the blood type systems. In addition, the blood type system also includes the aforementioned Rh type as well as MNS type, Kidd type, Kell type, Kx type, etc. According to statistics from the International Society of Blood Transfusion, as of September 2022, there are 43 recognized blood type systems and 349 red blood cell antigens in the world.

Source: pexels

Do you know about blood types?

In 1900, Austrian scientists discovered the phenomenon of red blood cell agglutination when studying the bodies of patients who died from blood transfusions, and thus discovered the ABO blood type . For this reason, for a long time, people believed that blood type was the type of antigen on red blood cells.

However, with the continuous deepening of research, people's definition of blood type has gradually expanded to white blood cells, platelets, serum proteins, etc. For example, in 1956, people detected serum immunoglobulin allotype Gm factor, in 1958 detected human leukocyte antigen HLA, in 1959 detected human platelet antigen HPA, in 1960 detected human neutrophil antigen HNA... However, in clinical practice, because ABO blood type and Rh blood type have the strongest immunogenicity, usually only ABO and Rh blood type identification is done before blood transfusion.

Source | pixabay

What blood type is CisAB?

CisAB blood type is a subtype of ABO blood type and was first discovered in 1930. ABO gene mutation will form subtypes of ABO blood type. For example, A gene mutation forms subtype A1 and subtype A2, and CisAB is an AB subtype.

Generally, the A gene and B gene of AB type are carried by two chromosomes respectively, which we call trans AB type. However, the A gene and B gene of CisAB type are on the same chromosome, so in order to distinguish it from trans AB type, we call it cis AB type.

There are two reasons for the emergence of CisAB blood type: one is gene exchange, and the other is gene mutation. The reason why CisAB blood type is of interest to the general public is that it does not conform to the general blood type inheritance law. If the parents are type O and type AB respectively, the child may be type AB or type O. It is unreliable to determine the parent-child relationship based solely on blood type.

Source: pexels

How to identify CisAB blood type?

Generally, people discover ABO subtypes when identifying ABO blood types, and then use auxiliary tests to determine which subtype it is. The red blood cell agglutination test is a classic method for identifying ABO blood types, which includes positive and negative typing. Positive typing uses anti-A or anti-B serum to detect whether there are corresponding A antigens or B antigens on red blood cells, while negative typing uses standard A cells or B cells to detect whether there are corresponding anti-A antibodies or anti-B antibodies in the serum.

Through positive and negative typing, it is possible to find antibodies of ABO subtypes, or there may be inconsistent typing conclusions or weak agglutination strength. The testers will find abnormalities in the serological reaction pattern, but they cannot determine the cisab blood type through serological reactions. Further blood type gene testing or even blood type gene sequencing is required for the final diagnosis.

Source of autologous blood recovery machine | Internet

How to transfuse blood with CisAB blood type?

Patients with CisAB blood type should use autologous blood transfusion, homologous blood transfusion or matched blood transfusion according to the blood transfusion standards for rare blood types. The matched blood transfusion here is the so-called general rule for difficult blood matching: use type O washed red blood cells, type AB plasma, and type AB platelets. If conditions permit, implement the autologous blood transfusion procedure. As for homologous blood transfusion of CisAB blood type, it is almost impossible to achieve in reality.

Source of the help information posted on the official website of the China Rare Blood Type Alliance | Screenshot of the official website of the China Rare Blood Type Alliance

Since it is difficult to match CisAB blood, can people with CisAB blood store their blood regularly for emergency use? The answer is that it is difficult. Even by adding reagents or freezing, blood cannot be preserved indefinitely, and it is inevitable that blood will be damaged during the storage process.

In order to preserve the various components of blood to the maximum extent, extend the "shelf life" and retain its biological functions, people will preserve the components of blood separately, and the "shelf life" and storage conditions of different blood components are different. For example, red blood cells can be preserved in liquid or frozen state. Liquid preservation can extend the "shelf life" to 12 weeks; although frozen preservation can be preserved for 10 years, the preparation is complicated and costly, and the preservation process will damage the cell membrane of red blood cells, affecting their physiological functions.

In contrast, the "shelf life" of white blood cells is shorter. After leaving the body, at 4°C, white blood cells can only be stored for 5 to 8 days, of which granulocytes will lose their function after 1 day, followed by lymphocytes, and finally monocytes. At present, lymphocytes can be frozen, but the storage method of granulocytes is still in the experimental stage. As for platelets , they are more fragile in nature and will soon be deformed and damaged after leaving the body, which greatly reduces the effect of blood transfusion. At room temperature, even if the pH environment and other conditions are suitable, platelets can only be stored for 3 to 7 days; and frozen platelets suffer great losses, and the hemostatic effect is only about 55% of fresh platelets.

If CisAB type patients are to undergo surgery that may involve heavy bleeding, they must plan well, and first of all, they must fully explain their situation to the doctor. The doctor will look for and allocate blood according to the actual situation, or after confirming that the patient meets the conditions through a series of tests and examinations, reserve the patient's blood for autologous blood transfusion.

At present, it is still difficult to give blood transfusion to people with CisAB blood type, and more attention should be paid to avoid injury and bleeding. In 2004, the China Rare Blood Type Alliance was established to provide voluntary services for patients with rare blood types who need blood transfusion, adding a layer of safety to their lives.

Source | pixabay

I believe that with the advancement of technology, scientists will surely make more breakthroughs, either by developing methods to extend the "shelf life" of various components in the blood, or by producing "artificial blood" that can replace human blood, completely changing the blood transfusion dilemma for people with rare blood types. Let us wait and see.