# Human blood group systems

The term human blood group systems is defined by the International Society of Blood Transfusion (ISBT) as systems in the human species where cell-surface antigens—in particular, those on blood cells—are "controlled at a single gene locus or by two or more very closely linked homologous genes with little or no observable recombination between them", and include the common ABO and Rh (Rhesus) antigen systems, as well as many others; 47 human systems are identified as of 30 September 2024.

## Table of systems and classifications

| ISBT No. | System name | System symbol | Structure / function | Chromosome | Antigens | Notes |
| 001 | ABO | ABO | Carbohydrate (N-Acetylgalactosamine, galactose). | 9q34.2 | A, B, H | Mainly elicit IgM antibody reactions, although anti-H is very rare, see the Hh antigen system (Bombay phenotype, ISBT #18). |
| 002 | MNS | MNS | GPA / GPB (glycophorins A and B). | 4q31.21 | M, N, S, s | |
| 003 | P1PK | P | Glycolipid | 22q13.2 | P$_1$, P, and P$^k$ | |
| 004 | Rh | RH | Protein and glucose. | 1p36.11 | C, c, D, E, e | There is no "d" antigen; lowercase "d" indicates the absence of D. |
| 005 | Lutheran | LU | Protein (member of the immunoglobulin superfamily). | 19q13.32 | 21 antigens | |
| 006 | Kell | KEL | Glycoprotein. | 7q34 | K, k, Kp$^a$, Kp$^b$, Js$^a$ and Js$^b$ | |
| 007 | Lewis | LE | Carbohydrate (fucose residue). | 19p13.3 | Mainly Le$^a$ and Le$^b$ | Associated with tissue ABH antigen secretion. |
| 008 | Duffy | FY | Protein (chemokine receptor). | 1q23.2 | Mainly Fy$^a$ and Fy$^b$ | Individuals lacking Duffy antigens altogether are immune to malaria caused by Plasmodium vivax and Plasmodium knowlesi. |
| 009 | Kidd | JK | Protein (urea transporter). | 18q12.3 | Jk$^a$ and Jk$^b$ | |
| 010 | Diego | DI | Glycoprotein (band 3, AE 1, or anion exchange). | 17q21.31 | | Positive blood is found only among East Asians and Native Americans. |
| 011 | Yt | YT | Protein (AChE, acetylcholinesterase). | 7q22.1 | | |
| 012 | XG | XG | Glycoprotein. | Xp22.33 | | |
| 013 | Scianna | SC | Glycoprotein. | 1p34.2 | | |
| 014 | Dombrock | DO | Glycoprotein (fixed to cell membrane by GPI, or glycosyl-phosphatidyl-inositol). | 12p12.3 | | |
| 015 | Colton | CO | Aquaporin 1. | 7p14.3 | Mainly Co(a) and Co(b) | |
| 016 | Landsteiner-Wiener | LW | Protein (member of the immunoglobulin superfamily). | 19p13.2 | | |
| 017 | Chido/Rodgers | CH | C4A C4B (complement fractions). | 6p21.3 | | |
| 018 | Hh | H | Carbohydrate (fucose residue). | 19q13.33 | | |
| 019 | XK | XK | Glycoprotein. | Xp21.1 | | |
| 020 | Gerbich | GE | GPC / GPD (Glycophorins C and D). | 2q14.3 | | |
| 021 | Cromer | CROM | Glycoprotein (DAF or CD55, regulates complement fractions C3 and C5, attached to the membrane by GPI). | 1q32.2 | | |
| 022 | Knops | KN | Glycoprotein (CR1 or CD35, immune complex receptor). | 1q32.2 | | |
| 023 | Indian | IN | Glycoprotein (CD44 adhesion function?). | 11p13 | | |
| 024 | Ok | OK | Glycoprotein (CD147). | 19p13.3 | | |
| 025 | Raph | RAPH | Transmembrane glycoprotein. | 11p15.5 | | |
| 026 | JMH | JMH | Protein (fixed to cell membrane by GPI). Also known as Semaphorin 7A or CD108. | 15q24.1 | | |
| 027 | Ii | I | Branched (I) / unbranched (i) polysaccharide. | 6p24.2 | | |
| 028 | Globoside | GLOB | Glycolipid. Antigen P. | 3q26.1 | | |
| 029 | GIL | GIL | Aquaporin 3. | 9p13.3 | | |
| 030 | Rh-associated glycoprotein | RHAg | Rh-associated glycoprotein. | 6p21-qter | | |
| 031 | Forssman | FORS | Globoside alpha-1,3-N-acetylgalactosaminyltransferase 1 (GBGT1). | 9q34.13 | | |
| 032 | Langereis | LAN | ABCB6, human ATP-binding cassette (ABC) transporter, mitochondrial porphyrin transporter. | 2q36 | | |
| 033 | Junior | JR | ABCG2. Multi-drug transporter protein. | 4q22 | | |
| 034 | Vel | Vel | Human red cell antigens. | 1p36.32 | | |
| 035 | CD59 | CD59 | — | 11p13 | | |
| 036 | Augustine | AUG | Protein (transporter). | 6p21.1 | | |
| 037 | KANNO | PRNP | — | 20p13 | | |
| 038 | SID | SID | | 17q21.32 | | |
| 039 | CTL2 | CTL2 | | 19p13.2 | | |
| 040 | PEL | PEL | | 13q32.1 | | |
| 041 | MAM | MAM | | 19q13.33 | | |
| 042 | EMM | EMM | | 4p16.3 | | |
| 043 | ABCC1 | ABCC1 | | 16p13.11 | | |
| 044 | Er | Er | Protein | 16q24.3 | Er$^a$, Er$^b$, Er3, Er4, and Er5 | Illustrates potential antigenicity of low abundance membrane proteins and contributes to understanding of in vivo characteristics of the Piezo1 protein in transfusion biology |
| 045 | CD36 | CD36 | | 7q21.11 | | |
| 046 | ATP11C | ATP11C | | Xq27.1 | | |
| 047 | MAL | MAL | | 2q11.1 | | |

## Antibodies

Following is a comparison of clinically relevant characteristics of antibodies against the main human blood group systems:
| | ABO | Rh | Kell | Duffy | Kidd | Lutheran | MNS | Lewis | P | Ii |
| Most common in immediate hemolytic transfusion reactions | A | | Yes | Fy$^a$ | Jk$^a$ | | | | | |
| Most common in delayed hemolytic transfusion reactions | | E,D,C | | | Jk$^a$ | | | | | |
| Most common in hemolytic disease of the newborn | Yes | D,C | Yes | | | | | | | |
| Commonly produce intravascular hemolysis | Yes | | | | Yes | | | | Yes | |
| Reactive at room temperature | Yes | | | | | | M,N | Le$^a$, Le$^b$ | P1 | |
| Nearly always clinically insignificant | | | | | | Yes | M,N | Yes | P1 | |
| Naturally occurring | Yes | | | | | Yes | M,N | Yes | Yes | Yes |
| Enhanced by ficain and papain | Yes | Yes | | | Yes | | | Yes | P1 | Yes |
| Destroyed by ficain and papain | | | | Fy$^a$, Fy$^b$ | | Yes | Yes | | | |
| Displaying dosage Further information: Blood compatibility testing | | Cc, Ee | | Yes | Yes | | Yes | | | |

## Compatibility testing

Blood compatibility testing is performed before blood transfusion, including matching of the ABO blood group system and the Rh blood group system, as well as screening for recipient antibodies against other human blood group systems. Blood compatibility testing is also routinely performed on pregnant women and on the cord blood from newborn babies, because incompatibility puts the baby at risk for developing hemolytic disease of the newborn. It is also used before hematopoietic stem cell transplantation, as it may be responsible for some cases of acute graft-versus-host disease.
Other human blood group systems than ABO and Rh have a relatively small risk of complications when blood is mixed. Therefore, in emergencies such as major hemorrhage, the urgency of transfusion can exceed the need for compatibility testing against other blood group systems (and potentially Rh as well). Also, blood compatibility testing beyond ABO and Rh is generally limited to antibody detection (not necessarily including forward typing). Still, in Europe, females who require blood transfusions are often typed for the K and extended Rh antigens to prevent sensitization to these antigens, which could put them at risk for developing hemolytic disease of the newborn during pregnancy.
When needing to give red blood cell transfusion to a patient, the presence of clinically significant antibodies produced by the patient can be detected by mixing patient serum with 2 to 4 "screening" or "control" red blood cells that together display essentially all relevant antigens. If any of these mixes display a reaction (evidence of patient antibodies binding to the screening red blood cells), a more extensive antibody panel is warranted (as imaged at right).