Rhesus Factor and Anti-D Immunoglobulin Use

Rhesus (RhD) factor and anti‑D immunoglobulin - ED revision

This section summarises practical emergency‑department management to prevent RhD alloimmunisation: indications, timing and typical doses of anti‑D immunoglobulin, the role and limits of fetomaternal haemorrhage (FMH) testing, and key logistical and safety points. Recommendations reflect UK guidance (NICE TA156, NG126, DG25). Always follow local transfusion and maternity policy.

Why RhD matters

• RhD is an antigen on red cells; an RhD‑negative mother exposed to RhD‑positive fetal red cells may become sensitised and develop anti‑D IgG antibodies.
• Maternal anti‑D IgG can cross the placenta in later pregnancies and cause haemolytic disease of the newborn (HDN), leading to fetal anaemia, hydrops fetalis, or perinatal death.
• Anti‑D immunoglobulin is pooled human IgG that prevents maternal sensitisation by binding fetal RhD‑positive red cells in the maternal circulation and promoting their clearance.
• Anti‑D immunoglobulin does not treat existing maternal anti‑D antibodies.

Key ED principles

• Check maternal blood group and antibody screen if unknown.
• If the mother is already sensitised (anti‑D positive), anti‑D prophylaxis is not indicated; refer to obstetrics/haematology for fetal surveillance.
• Give event‑driven anti‑D promptly after a potentially sensitising event (PSE); the standard target is within 72 hours.
• Some benefit may be retained if anti‑D is given after 72 hours and local policy may allow administration up to ~10 days, but do not delay urgent care...