Rh (D) Type

Shows whether your red blood cells carry the Rh (D) protein: positive if they do, negative if not. It matters for transfusions and pregnancy.

AI-verified against cited sources. Awaiting expert reviewAlso called Rh, RhD, Rh(D)LOINC 10331-7

What it is

Rh factor, also called RhD, is a protein on the surface of red blood cells. If your cells have it, you are Rh positive. If they don't, you are Rh negative. It is the plus or minus in a blood type like O positive or A negative, and you inherit it from your parents. Rh typing is a simple blood test, usually done together with ABO typing. Being Rh negative is a normal variation: roughly 15 in 100 people in North America are Rh negative, and it is less common in some other parts of the world.

Why it matters

Your Rh type tells a blood bank which red cells are safe to give you: if you are Rh negative, you should receive Rh negative red cells. It matters most in pregnancy. If you are Rh negative and your baby is Rh positive, your body can make antibodies that may harm the baby in a later pregnancy. This can be prevented, which is why Rh type is checked at the first prenatal visit. Rh type by itself is not a sign of illness.

What can affect your result

Inheritance: your Rh type comes from your parents' genes and does not change over your life
Weak D or partial D: when red cells carry fewer or altered D proteins, labs may report 'weak D' or 'partial D', and policies for calling you positive or negative differ between labs
A recent transfusion or donor stem cell transplant can make typing harder to read
Ancestry: Rh negative is more common in some groups than others (about 15% in North America, about 5% in India)
A weak D result can be reported as Rh positive by one lab and Rh negative by another, because labs follow different policies. Many labs run a gene test (RHD genotyping) when a weak D or conflicting result appears.
A recent transfusion or a stem cell transplant from a donor can make typing harder to read. The blood bank may use a different method or a new sample.
Rh immune globulin does not change your Rh type, but it can make the antibody screen read positive.
Lab handling: Mayo Clinic Laboratories runs ABO/Rh typing by hemagglutination on an EDTA (pink-top) tube.

Your Rh type is inherited and does not change over time.

When to talk to a clinician

Your Rh type is not an urgent result. If you are pregnant and Rh negative, tell your care team right away about vaginal bleeding, a hit to the belly or a pregnancy loss, because you may need treatment soon afterward to prevent antibodies.

Questions you could ask

Was my result confirmed, or was a weak D result reported?
If I am Rh negative and pregnant or planning a pregnancy, what is the plan for my care?

Questions people ask

What does it mean to be Rh negative?

It means your red blood cells don't carry the Rh (D) protein. About 15 in 100 people in North America are Rh negative, and it is a normal variation, not an illness. It matters for blood transfusions and for pregnancy, where your care team can take steps to protect future pregnancies.

What is weak D?

Weak D means your red cells carry fewer D proteins than usual. Most people with weak D behave like Rh positive people, but a few have an altered D protein and are handled more carefully. Labs differ in how they report it, and a gene test often settles the question. Ask your clinician how your result will be used.

Can my Rh type change, or differ between labs?

Your Rh type is inherited and stays the same. If two reports differ, it is usually because of weak D or different lab rules for reporting it. Ask your clinician which result they are using.

Show the science and sources

For clinicians and researchers

Rh D typing uses anti-D reagents with hemagglutination (tube, gel or solid-phase); Mayo Clinic Laboratories' ABO/Rh test (ABOMR) uses hemagglutination on EDTA whole blood and reports 'ABO and Rh blood group antigens identified' under LOINC 882-1. The prevalence of RhD-negative status ranges from about 5% in India to 15% in North America (ACOG Practice Bulletin 181); in the US, Stanford Blood Center lists O negative 6.6%, A negative 6.3%, B negative 1.5% and AB negative 0.6%, about 15% in all. Reduced D expression falls into two groups: weak D, where the red cells carry fewer D antigens but are not missing major epitopes, and partial D, where epitopes are missing and there is a risk of making anti-D (Vege 2021). A serologic weak D phenotype is found in about 0.6% to 1.0% of white individuals, mostly weak D types 1, 2 and 3, which can be treated as RhD positive. RHD genotyping is recommended when a weak D phenotype or a typing discrepancy appears, to guide transfusion and Rh immune globulin decisions (Canadian Family Physician 2020; Vege 2021). About 60% of RhD-negative pregnant people carry an RhD-positive fetus, and fetal RhD status is usually unknown until delivery, so Rh-negative patients without immune anti-D are offered antenatal Rh immune globulin. ACOG Practice Bulletin 181 covers prevention of Rh D alloimmunization with Rh immune globulin. Combined ABO and Rh results (for example 'O Pos', LOINC 882-1) are split into the ABO and Rh markers.

LOINC 10331-7 (primary), 882-1. Specimen: whole-blood.

Sources

The Rh Factor: How It Can Affect Your Pregnancy, American College of Obstetricians and Gynecologists (2022)
Practice Bulletin No. 181: Prevention of Rh D Alloimmunization, Obstetrics & Gynecology (ACOG) (2017)
Approach to red blood cell antibody testing during pregnancy: Answers to commonly asked questions, Canadian Family Physician (2020)
Blood Types, Stanford Blood Center
Impact of RHD genotyping on transfusion practice in Denmark and the United States and identification of novel RHD alleles, Transfusion (2021)
Blood typing, MedlinePlus Medical Encyclopedia, National Library of Medicine
ABO/Rh, Blood (test ABOMR), Mayo Clinic Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.