The blood type known colloquially as "monkey blood" is the Rh factor, or Rhesus factor.
The fascinating informal name for this crucial blood component stems directly from its discovery. In 1939, pioneering researchers Karl Landsteiner and Alexander S. Wiener identified a particular antigen in human red blood cells. At the time of their discovery, they believed this antigen was strikingly similar to one found in the red blood cells of the rhesus macaque monkey. This association with the rhesus monkey led to the naming of the "Rhesus factor," which was later abbreviated to "Rh factor," and consequently, its popular nickname, "monkey blood."
Understanding the Rh Factor
The Rh factor is an inherited protein that resides on the surface of red blood cells. Its presence or absence is a vital aspect of an individual's blood type, classifying them as either Rh-positive (Rh+) or Rh-negative (Rh-).
- Rh-Positive (Rh+): Individuals with the Rh factor protein on their red blood cells are considered Rh-positive. The majority of the human population (approximately 85%) is Rh-positive.
- Rh-Negative (Rh-): Individuals who do not have the Rh factor protein on their red blood cells are considered Rh-negative.
Why is the Rh Factor Important?
Understanding an individual's Rh status is critical, particularly in two key medical scenarios: blood transfusions and pregnancy.
1. Blood Transfusions
Matching Rh types is just as important as matching ABO blood types during transfusions.
- An Rh-negative person receiving Rh-positive blood can develop antibodies against the Rh factor. While the first transfusion might not cause severe issues, subsequent exposure to Rh-positive blood can lead to a serious immune reaction, where the body's immune system attacks the transfused red blood cells.
- Conversely, an Rh-positive person can safely receive either Rh-positive or Rh-negative blood.
2. Pregnancy and Rh Incompatibility
Rh incompatibility can pose risks during pregnancy when an Rh-negative mother carries an Rh-positive baby.
- If an Rh-negative mother is exposed to the Rh-positive blood of her baby (which can happen during childbirth, miscarriage, or certain medical procedures), her immune system may recognize the Rh factor as foreign and produce antibodies against it.
- These antibodies typically do not affect the current pregnancy, but they can cross the placenta in subsequent pregnancies. If a future baby is also Rh-positive, the mother's antibodies can attack the baby's red blood cells, leading to a serious condition known as hemolytic disease of the fetus and newborn (HDFN), also called Rh disease.
- Modern medicine has a highly effective solution: Rh immune globulin (RhoGAM). This injection, given to Rh-negative mothers during pregnancy and after birth, prevents the mother from forming antibodies against Rh-positive blood, safeguarding future Rh-positive pregnancies.
Combined Blood Type Systems
The Rh factor is always considered in conjunction with the ABO blood group system (A, B, AB, O) to determine a person's complete blood type. For example, a person's blood type could be A-positive (A+), O-negative (O-), B-positive (B+), or AB-negative (AB-), among others.
Here's a simplified look at how the Rh factor influences common blood types:
| Blood Type | ABO Antigens | Rh Factor | Notes |
|---|---|---|---|
| A+ | A | Present | Most common blood type for people with A antigens. |
| A- | A | Absent | Individuals can only receive A- or O- blood. |
| B+ | B | Present | Common for people with B antigens. |
| B- | B | Absent | Can receive B- or O- blood. |
| AB+ | A and B | Present | Universal Recipient – can receive blood from all ABO and Rh types because they have all common antigens. |
| AB- | A and B | Absent | Can receive A-, B-, AB-, or O- blood. Often considered a "rare" blood type due to the combination of AB and Rh-negative. |
| O+ | None | Present | Universal Donor (for Rh+ recipients) – can donate to all positive blood types (A+, B+, AB+, O+). |
| O- | None | Absent | Universal Donor – can donate to all ABO and Rh types, making it highly valuable in emergencies. They can only receive O- blood themselves. |
For further information on the Rh blood group system, you can refer to resources like the Rh blood group system on Wikipedia.
