Platelet Size
Individuals with inherited platelet disorders experience lifelong abnormal bleeding, usually at mucocutaneous sites or elsewhere after trauma or invasive procedures. Inherited platelet disorders should be suspected in patients with lifelong thrombocytopenia; bleeding not explained by a coagulation factor deficiency; presentation with an associated condition; and patients with affected family members. Inherited platelet disorders can be caused by defects in surface membrane receptors, signaling pathways, granule formation and secretion, cytoskeletal remodeling and expression of procoagulant activity.
Laboratory testing for suspected inherited platelet disorders should begin with a complete blood count (CBC) and examination of a peripheral blood smear. CBC includes platelet count and mean platelet volume (MPV). An abnormal platelet count and MPV should be confirmed by examination of a peripheral blood smear. The following table contains a summary of platelet count and platelet size in various platelet disorders.
| Platelet Disorder | Platelet Count Reduction | Platelet Size |
| Bernard Soulier | Moderate to severe | Giant |
| Familial platelet disorder associated with AML | Mild to moderate | Normal |
| GATA1-related thrombocytopenia | Severe | Large |
| Gray platelet syndrome | Mild | Large |
| Medich platelet syndrome | Mild | Large |
| MYH9 mutation associated disorders | Mild to moderate | Large |
| Paris-Trousseau syndrome | Moderate to severe | Normal to slightly increased |
| Platelet type vWD | Mild | Normal or slightly increased |
| Stormorken syndrome | Mild to moderate | Normal |
| Velocardiofacial syndrome | Mild | Large |
| Wiskott-Aldrich | Severe | Small |
| White platelet syndrome | Mild | Large |
Reference range for MPV is 7.4-11.5 fL. MPV <6 fL is seen in Wiskott Aldrich syndrome and MPV >12 is seen in Bernard Soulier. If the platelet count and platelet size suggest that an inherited platelet disorder may be present, platelet function analysis (PFA-100) and platelet aggregation should be ordered. Abnormal findings in these tests may necessitate additional confirmatory tests including platelet electron microscopy, platelet flow cytometry and genotyping.
