Table II.

Characteristics of the various forms of AIHA.

Clinical form	Frequency (%)	DAT	Ig class	Thermal optimum (°C)	Avidity and ability to fix complement	Antigen specificity	Site of haemolysis
Warm antibodies	60–70	IgG+ or IgG+/C3d+	IgG	34–37	−/+	Anti-Rh	Extravascular
Cold antibodies	20–25	Neg. or C3d+	IgM	4–27	+++	Anti-I	Extravascular and intravascular
Cold paroxysmal haemoglobinuria	6–12	Neg. or C3d+	IgG Biphasic	Fixing 4–27 Lysis 34 37	+++	Anti-P	Intravascular
Mixed AEA	< 5	IgG+ or IgG+/C3d+ or C3d+	IgG/IgM	IgG 34–37 IgM 4–27	++	Anti-Rh Anti-I	Extravascular and intravascular

AIHA: autoimmune haemolytic anaemia; DAT: direct antiglobulin test; Ig: immunoglobulin; AEA: anti-erythrocyte autoantibodies; Neg.: negative.