The film was prepared from a 6-year-old boy with febrile illness presented with intravascular haemolysis and haemoglobinuria. His blood profile was: WBC 20.9 x 10⁹/L, RBC 2.41 x 10¹²/L, Hb 6.9 g/dL, Hct 0.200 L/L, MCV 83.1 fL and Plt 339 x 10⁹/L. The prominent features of the blood film are erythrophagocytosis and toxic granulations (Figures 1 - 4). There is moderate leukocytosis and the white cell differential shows neutrophilia with left shift. The red cell population exhibits moderate spherocytosis. Mild polychromasia and anisocytosis are also noted. Platelet count is adequate. Intravascular haemolysis is evident. These are suggestive of paroxysmal cold haemoglobinuria (PCH).

PCH is characterized by a sudden onset haemoglobinuria either spontaneously or after exposure to cold due to the presence of a cold reacting polyclonal IgG Donath-Landsteiner autoantibody. The event triggering autoimmune response may be attributable to the exposure of a microorganism mimicking the red blood cell P antigen. The Donath-Landsteiner autoantibody is a biphasic haemolysin which tends to bind RBC at cooler temperatures and complement lysis occurs at warmer temperatures. These characteristics have thus formed the basis of the Donath-Landsteiner test which is diagnostic for PCH. Direct antiglobulin test, if performed, can be positive for poly-specific AHG and anti-C3d, but negative for anti-IgG because of dissociation of IgG from RBC at higher temperatures. The disease is usually associated with a recent respiratory or other viral infection in children, and the illness is transient and self-limiting particularly if the primary infection can be adequately treated.

Figure 1.  Erythrophagocytosis in neutrophils (1,000x magnification).

Figure 2.  Hyper-granulation and vacuolation in polymorphonuclear cells (1,000x magnification).

Figure 3.  Erythrophagocytosis in neutrophils (1,000x magnification).

Figure 4.  Phagocytosis of multiple red blood cells in neutrophils (1,000x magnification).