Table I. Comparison of murine, canine and human platelets and canine and murine ITP model systems.

	Humans	Mice	Dogs
Spontaneous ITP?	Yes	No (Semple, 2010)	Yes (Lewis & Meyers, 1996)
Platelet counts	150-400 × 109/l	1 million/μl (Ware, 2004)	190-468 × 109/l
Platelet volumes	7.5-10 fl	4.7 ± 0.3 fl(Ware, 2004)	7.9-13.8 fl
Platelet protease activated-receptors (PAR)	PAR 1 and 4 (Ware, 2004)	PAR 3 and 4 (Ware, 2004)	PAR 1 and 4 (Boudreaux et al, 2007)
Blood volume that can be safely sampled	N/A	0.2 ml (Diehl et al, 2001) (25 g mouse)	85 ml (Diehl et al, 2001) (10 kg dog)
Animal survival studies possible?	N/A	No	Yes
Result of ITP models utilizing antibodies to the fibrinogen receptor (GPIIbIIIa)	Variable bleeding, no systemic symptoms other than fatigue (with spontaneous disease)	Acute systemic reactions, hypothermia, incoordination (Nieswandt et al, 2000)	Variable bleeding, no systemic signs other than those relating to haemorrhage (Lewis & Meyers, 1996; O'Marra et al, 2011)

ITP, immune thrombocytopenia; GPIIbIIIa, glycoprotein IIbIIIa complex; N/A, not applicable.