Contents · 9 sections
Blood groups are studied three times: in physiology (antigens and agglutination), general surgery (transfusion and tests), and obstetrics (rhesus incompatibility). Examiners across all three departments love compatibility tables and inheritance problems. Below is everything you need in tables, plus transfusion rules as practiced in Russia.
AB0 system: antigens and antibodies
| Group | Parameter | Erythrocyte antigens | Plasma antibodies | Prevalence in Russia |
|---|---|---|---|---|
| I | 0 (αβ) | No | Anti-A (α) and anti-B (β) | ~33 % |
| II | A (β) | A | Anti-B (β) | ~37 % |
| III | B (α) | B | Anti-A (α) | ~21 % |
| IV | AB (0) | A and B | No | ~9 % |
Landsteiner's rule: a person's blood never contains corresponding antigens and antibodies simultaneously (e.g., A and anti-A). AB0 antibodies are natural, appearing in the first months of life without prior exposure to foreign red blood cells; this distinguishes them from rhesus antibodies.
Rhesus factor
The rhesus system includes several antigens (D, C, c, E, e); "rhesus-positive" means the presence of the D antigen, which is the most immunogenic. Rh+ comprises about 85% of Europeans, and Rh− comprises 15%. There are no natural antibodies to the D antigen: they form only after an Rh− person is exposed to Rh+ red blood cells via transfusion or pregnancy. Therefore, the first transfusion of rhesus-incompatible blood may pass without a reaction, while the second can cause hemolysis.
Erythrocyte compatibility
| Recipient ↓ / Donor → | 0− | 0+ | A− | A+ | B− | B+ | AB− | AB+ |
|---|---|---|---|---|---|---|---|---|
| 0− | ✓ | |||||||
| 0+ | ✓ | ✓ | ||||||
| A− | ✓ | ✓ | ||||||
| A+ | ✓ | ✓ | ✓ | ✓ | ||||
| B− | ✓ | ✓ | ||||||
| B+ | ✓ | ✓ | ✓ | ✓ | ||||
| AB− | ✓ | ✓ | ✓ | ✓ | ||||
| AB+ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
Logic: donor red blood cells must not carry antigens against which the recipient has antibodies. 0− is the "universal donor" of red blood cells, and AB+ is the "universal recipient." This is a study model: in clinical practice, identical blood groups and rhesus types are transfused, while mismatched blood is used only for life-saving indications when matching blood is unavailable, and in limited volumes.
Plasma compatibility
Plasma works in reverse: donor antibodies are transfused, and they must not encounter recipient antigens. AB plasma contains no antibodies, making it the universal plasma donor; a recipient with blood group 0 can receive plasma of any group. Rhesus status does not matter for plasma (the D antigen is on red blood cells), but standard protocol requires transfusing AB0-matched plasma.
Blood group inheritance
Blood groups are determined by the I gene with three alleles: IA and IB are codominant, while i is recessive. Genotypes: 0 — ii; A — IAIA or IAi; B — IBIB or IBi; AB — IAIB.
| Parents | Possible children's blood groups | Impossible |
|---|---|---|
| 0 × 0 | 0 | A, B, AB |
| 0 × A | 0, A | B, AB |
| 0 × B | 0, B | A, AB |
| 0 × AB | A, B | 0, AB |
| A × A | 0, A | B, AB |
| A × B | 0, A, B, AB | — |
| A × AB | A, B, AB | 0 |
| B × B | 0, B | A, AB |
| B × AB | A, B, AB | 0 |
| AB × AB | A, B, AB | 0 |
The rhesus factor is inherited as a simple dominant trait: D is dominant, and d is recessive. Two Rh+ parents (Dd × Dd) can have an Rh− child (dd, 25% chance); two Rh− parents can only have Rh− children. A rare exception in the AB0 system is the "Bombay phenotype": the absence of the H antigen makes an individual with the IA or IB genotype phenotypically 0, meaning a "zero-group" parent can have a child with blood group AB.
Blood typing
Direct method — monoclonal antibodies (anti-A, anti-B, anti-ABцоликлоны / tsoklikons): a drop of reagent is mixed with blood, and agglutination is assessed after 3–5 minutes. Agglutination with anti-A indicates group A, with anti-B indicates group B, with both indicates AB, and with neither indicates 0. The cross-matching method incorporates standard red blood cells to detect plasma antibodies and is mandatory in the laboratory prior to transfusion. Rhesus typing is performed using anti-D tsoklikon. Potential errors include hemolysis, low temperature (cold agglutinins), high protein concentration, and weak variants of the A antigen (A2).
Pre-transfusion tests
- Determination of the recipient's and donor's (from the container) blood group and rhesus type immediately before transfusion.
- Individual AB0 compatibility test: recipient serum + donor red blood cells at a 10:1 ratio, for 5 minutes at room temperature.
- Rhesus compatibility test (using 33% polyglucin or gelatin, or an indirect antiglobulin test in the laboratory).
- Biological test: three consecutive 10-ml rapid bolus injections separated by 3-minute intervals with patient monitoring.
No step may be skipped, even if the blood has been "laboratory-matched." Since the 2010s in Russia, the Kell antigen must also be taken into account: Kell-positive red blood cells are transfused exclusively to Kell-positive recipients.
Rhesus incompatibility in pregnancy
Rh− mother and Rh+ fetus: fetal red blood cells enter the maternal circulation (during childbirth, abortion, bleeding, or amniocentesis), triggering anti-D antibody production. In a subsequent pregnancy, these antibodies cross the placenta and destroy the Rh+ fetus's red blood cells, causing hemolytic disease of the fetus and newborn. Prevention: administration of anti-Rhesus immunoglobulin to an Rh− woman without antibodies at 28 weeks of gestation, within the first 72 hours after delivering an Rh+ child, and following any event carrying a risk of fetal-maternal hemorrhage. AB0 incompatibility (mother 0, child A or B) occurs more frequently but has a milder clinical course.
Frequently asked questions
Can parents with blood groups A and B have a child with blood group 0? Yes, if both are heterozygous (IAi × IBi) — a 25% probability.
Why can't 0− blood be transfused to everyone without prior testing? Besides AB0 and D, dozens of other antigens exist (Kell, Duffy, Kidd); individuals with a history of transfusions or pregnancies may have developed antibodies against them. Therefore, compatibility tests are mandatory for any combination.
Which blood group is the rarest? AB− — approximately 1% of the population.
See also: Hemostasis and blood coagulation · Blood formed elements · Anemias: classification · Physiology reference guide