Table III.

Haemovigilance for unexplained occurrence of anti-D.

Anti-D observed in:	Differential diagnosis
Rh-positive patient	Variant RHD allele
	possibly associated with variant RHCE allele
	Auto-anti-D (rare)
	Passively acquired anti-D (rarely free anti-D in recipient’s plasma)
Rh-negative patient*	Passively acquired anti-D
	by donor plasma, or
	by immunoglobulin-containing blood products: IVIG, RhIG
	Rh positive RBC unit, mislabelled as Rh negative
	Serologically negative RBC unit with a functional RHD allele expressing weak D or DEL phenotypes
	Naturally occurring anti-D (very rare, if ever)

^*Complete transfusion history particularly critical.

IVIG: intravenous immunoglobulin; RhIG: Rhesus immunoglobulin.