Positive or Negative? The Rh Factor Mystery

You know you are "A Positive" or "O Negative". But what is the plus or minus?

The Rhesus (Rh) D Antigen

Discovered in Rhesus monkeys, this protein sits on the surface of your red blood cells.

• Rh Positive (+): You HAVE the D antigen. (85% of people).
• Rh Negative (-): You LACK the D antigen. (15% of people).

Why It Matters

If you give Rh+ blood to an Rh- patient, their body will create antibodies to attack it. This can be fatal.

Pregnancy Risk: An Rh- mother carrying an Rh+ baby can develop antibodies that attack her *next* baby (Hemolytic Disease of the Newborn). This is why blood typing during pregnancy is mandatory.