Home Biomarkers Rh Factor

Rh Factor

CBC Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: CBC

Overview

The Rh factor (Rhesus D antigen) is a protein on the surface of red blood cells; the Rh test determines whether the D antigen is present (Rh‑positive) or absent (Rh‑negative). It is a categorical blood‑typing test used for transfusion compatibility, prenatal care, and investigation of hemolytic disease of the newborn (HDN). Testing is indicated when matching blood for transfusion, during pregnancy (mother and father), after miscarriages or bleeding events, and when unexplained hemolysis occurs. Rh status itself does not change with age, but clinical importance is greatest for women of childbearing age because an Rh‑negative mother can form anti‑D antibodies if exposed to Rh‑positive fetal blood.

People also test for

Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: commonly included with blood group typing/compatibility testing alongside CBC or pre‑transfusion panels.
Symptoms/indications: pregnancy care, after transfusion, unexplained anemia or jaundice in newborns, or following bleeding/miscarriage.
Diagnoses/monitoring: prevents/monitors alloimmunization and hemolytic disease of the fetus/newborn; ensures safe transfusions.
Reasons for abnormal: exposure to incompatible blood (pregnancy, transfusion, trauma) causing anti‑D antibody formation.
Biological meaning: presence of anti‑D antibodies can cause hemolysis of Rh‑positive red cells.
Lifestyle/factors: no routine lifestyle causes; sensitizing events (pregnancy bleeding, invasive obstetric procedures, transfusion) matter.
Family history: known Rh incompatibility or prior infant HDN in family increases the need for testing.

Run our symptom checker to see if this test is right for you

Symptom Checker

Understanding Test Results

Rh‑positive: D antigen detected compatible with most transfusions and not at risk of alloimmunization from a D‑positive fetus.
Rh‑negative: D antigen not detected clinically important if the person is pregnant or requires transfusion.
An Rh‑negative mother exposed to Rh‑positive fetal blood can develop anti‑D IgG antibodies; once formed, these can cross the placenta and cause fetal hemolysis.
Indirect antiglobulin (antibody) testing detects maternal anti‑D; rising or significant titers (commonly reported as ≥1:16 by many labs; some use ≥1:8 or ≥1:32) indicate increased risk of fetal anemia and require fetal monitoring.
A positive direct antiglobulin (Coombs) test in a newborn indicates antibody‑mediated hemolysis and may require phototherapy, IVIG, or exchange transfusion.
In transfusion settings, Rh‑negative patients should ideally receive Rh‑negative blood; emergency Rh‑mismatched transfusion risks alloimmunization and hemolytic reactions.
Special cases include weak D/partial D results that require further typing to determine appropriate transfusion and obstetric management.

Normal Range

Rh positive (D antigen present) or Rh negative (D antigen absent) categorical result (no numeric units)

FAQs

Q: What does Rh factor mean?

A: Rh factor is a protein (primarily the D antigen) on red blood cells. Presence means Rh‑positive; absence means Rh‑negative. It’s inherited and important for blood transfusions and pregnancy: Rh incompatibility between mother and fetus can trigger immune reactions in later pregnancies. Rh status is routinely tested to guide safe transfusions and appropriate prenatal care.

Q: Is a positive Rh factor good?

A: Rh-positive means you have the D antigen on red blood cells. For most people it’s neither inherently good nor bad it’s simply a common blood type. Clinically it matters in pregnancy (an Rh‑negative mother carrying an Rh‑positive fetus may need monitoring and prophylaxis). For transfusion, Rh‑positive people can receive Rh‑positive or Rh‑negative blood but typically donate only to Rh‑positive recipients.

Q: What is a normal Rh factor?

A: Rh factor refers to the Rh(D) antigen on red blood cells. Normal can be either Rh‑positive (D antigen present) or Rh‑negative (absent), though most people (about 85%) are Rh‑positive. The Rh type is inherited and matters for blood transfusion compatibility and pregnancy, where Rh incompatibility may require monitoring or treatment.

Q: Why is Rh negative so rare?

A: Rh-negative blood is uncommon because it stems from absence of the RhD antigen due to variants or deletions in the RHD gene on chromosome 1. The D-negative trait is inherited and occurs at low frequency. Historical founder effects, genetic drift, limited gene flow and population history rather than widespread advantage have kept the Rh‑negative allele rare globally, concentrated in some European groups.

Q: What happens if Rh is high?

A: High anti‑Rh antibodies in an Rh‑negative mother can cross the placenta and destroy fetal red blood cells, causing fetal anemia, jaundice, hydrops fetalis, heart failure or stillbirth. Management includes antibody titers, Doppler MCA monitoring, intrauterine transfusions or early delivery when needed. Prevention: giving anti‑D (Rh) immunoglobulin to Rh‑negative mothers after sensitizing events and postpartum reduces future risk.

Q: What happens if the Rh factor is high?

A: If someone develops a high Rh antibody level (sensitization), antibodies can cross the placenta in pregnancy and destroy fetal red blood cells, causing anemia, jaundice, hydrops fetalis or even stillbirth. In transfusion, Rh incompatibility can cause hemolytic reactions. Management includes antibody monitoring, IgG anti‑D prophylaxis for Rh‑negative mothers, close fetal surveillance, and possible intrauterine or neonatal transfusion.