[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Blood, hemostasis and basic immunity](https://durgical.com/en/physiology/#s-blood) › Blood groups, transfusion and transfusion reactions

[Physiology](https://durgical.com/en/physiology/) · [Blood, hemostasis and basic immunity](https://durgical.com/en/physiology/#s-blood)

# Blood groups, transfusion and transfusion reactions

- Concept
- Exam priority: high

Red cells carry sugar and protein labels (A, B, Rh). Giving blood with the wrong label makes the patient's antibodies destroy it.

Updated 2026-11-01

Also called: ABO system, Rh system, Blood typing

**See it in 3D:** [Spleen](https://durgical.com/en/anatomy/spleen/) · [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Key points

- Anti-A and anti-B are 'natural' IgM antibodies made in the first months of life, likely after exposure to similar gut bacterial antigens; they fix complement and cause intravascular hemolysis.
- Group O red cells (no A or B) are the emergency universal red cell donor; group AB is the universal plasma donor (no anti-A or anti-B).
- Rh antibodies are IgG, appear only after sensitization (transfusion or pregnancy) and can cross the placenta.
- Acute hemolytic reaction (usually ABO, clerical error): fever, back pain, hypotension, red urine, DIC and acute kidney injury within minutes.
- Anaphylaxis during transfusion: think of IgA deficiency with anti-IgA antibodies.
- Delayed hemolytic reaction 3–10 days later: memory IgG against a minor antigen (Kidd, Rh); extravascular, mild jaundice and falling Hb.

## What it is

Blood groups are inherited antigens on the red cell surface. In the ABO system, people make antibodies against the A or B antigen they lack, without ever being transfused; the RhD system needs prior exposure. Matching donor cells to the recipient's antibodies prevents hemolytic reactions, the most dangerous and most preventable error in transfusion.

## Key facts

- A and B antigens are sugars added by glycosyltransferases to the H substance; group O lacks a working transferase.
- Cross-match: recipient serum is tested against donor cells; the antibody screen looks for unexpected IgG.
- Stored red cells lose 2,3-BPG and K⁺ leaks out; massive transfusion can cause hyperkalemia, hypocalcemia (citrate) and hypothermia.
- In Colombia group O RhD-positive is the most common (around six in ten people) and RhD-negative is uncommon.

### Oxygen–hemoglobin dissociation curve

**P50** 16.5 mmHg **Arterial blood** 99 % **Mixed venous blood** 92 % **O₂ given up to the tissues** 8 %

Left shift (P50 16.5 mmHg): Hb holds O₂ more tightly and gives up less in the tissues.

- Current curve
- Normal curve (pH 7.40 · 37 °C)
- Arterial blood (PO₂ 100)
- Mixed venous blood (PO₂ 40)
- O₂ given up to the tissues

The 'stored blood' scenario: low 2,3-BPG shifts the curve left, so freshly transfused cells release O₂ less easily until they regenerate it.

## ABO groups

| Group | Antigen on red cells | Antibodies in plasma | Can receive red cells from |
| --- | --- | --- | --- |
| A | A | Anti-B | A, O |
| B | B | Anti-A | B, O |
| AB | A and B | None | AB, A, B, O |
| O | None | Anti-A and anti-B | O only |

## Clinical notes

- Acute hemolytic reaction: antibody binds donor cells → complement → intravascular lysis → free Hb, hemoglobinuria, cytokine storm, DIC; free Hb and hypotension injure the kidney.
- Febrile non-hemolytic reaction: cytokines from donor leukocytes; leukoreduction lowers the risk.
- TRALI (lung injury within 6 h, normal filling pressures) versus TACO (volume overload, high filling pressures): both cause dyspnea and hypoxemia.

## Memory aid

O is 'zero' antigens on the cell: it can go to anyone. AB has 'all' antigens and no antibodies: its plasma can go to anyone.

## Test yourself

Think of the answer, then tap the question to see it.

## Why can a group A person react to group B blood at the very first transfusion?

Anti-B is a natural IgM present from early infancy, so no prior exposure to human B cells is needed. In contrast, anti-D usually requires prior sensitization.

## Why is ABO hemolysis intravascular while most delayed reactions are extravascular?

IgM anti-A/B activates complement up to the membrane attack complex and lyses cells in the vessel. IgG on cells without full complement leads macrophages in the spleen to remove them.

## A patient becomes hypotensive with urticaria and wheeze minutes into a plasma transfusion. Which immune defect should be suspected?

IgA deficiency with anti-IgA antibodies: the IgA in donor plasma triggers an anaphylactic reaction.

## Why does massive transfusion of stored red cells lower ionized calcium?

Stored blood contains citrate as anticoagulant; citrate binds calcium, and when large volumes are given faster than the liver metabolizes citrate, ionized Ca²⁺ falls.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/blood-groups-transfusion-and-transfusion-reactions/)

## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Spleen](https://durgical.com/en/anatomy/spleen/)
- [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Related topics

- [Rh incompatibility](https://durgical.com/en/physiology/rh-incompatibility/)
- [The red cell life cycle and the spleen](https://durgical.com/en/physiology/the-red-cell-life-cycle-and-the-spleen/)
- [Innate and adaptive immunity: overview](https://durgical.com/en/physiology/innate-and-adaptive-immunity-overview/)
- [Anemia physiology and compensation](https://durgical.com/en/physiology/anemia-physiology-and-compensation/)

## Related conditions

- [Neonatal jaundice](https://durgical.com/en/conditions/neonatal-jaundice/)
- [Anaphylaxis](https://durgical.com/en/conditions/anaphylaxis/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)

## In Biochemistry

- [Immunoglobulins (antibodies)](https://durgical.com/en/biochemistry/enzymes/immunoglobulins/)
- [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [18.6 Blood Typing](https://openstax.org/books/anatomy-and-physiology-2e/pages/18-6-blood-typing) (OpenStax (Rice University), 2022); [Hemolytic transfusion reaction](https://medlineplus.gov/ency/article/001303.htm) (MedlinePlus (U.S. National Library of Medicine), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 36). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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