Platelet size distinguishes between inherited macrothrombocytopenias and immune thrombocytopenia.
BACKGROUND
Distinguishing inherited thrombocytopenias from immune thrombocytopenia (ITP) can be difficult, and patients are therefore at risk of misdiagnosis and inappropriate treatments. Although it is known that the most common inherited forms of thrombocytopenia are characterized by increased platelet size, the diagnostic power of this feature has never been investigated.


OBJECTIVE
The aim of this study was to test the hypothesis that platelet size can be used to differentiate ITP from inherited macrothrombocytopenias.


METHODS
We measured mean platelet volume (MPV) and mean platelet diameter (MPD), within 2 h of blood sampling, in 35 patients with inherited macrothrombocytopenias [15 MYH9-related disease (MYH9-RD), three biallelic and 17 monoallelic Bernard-Soulier syndrome (BSS)], and 56 with ITP. Using receiving operating characteristic analysis, we searched for the best cut-off values to differentiate between these conditions.


RESULTS
As expected, platelets were larger in inherited macrothrombocytopenias than in ITP. An MPD larger than 3.3 mum differentiated MYH9-RD and BSS from ITP with 0.89 sensitivity and 0.88 specificity, and an MPV larger than 12.4 fL had 0.83 sensitivity and 0.89 specificity. Combining MPD with MPV increased sensitivity and specificity to 0.97 and 0.89, respectively.


CONCLUSIONS
Platelet size evaluation by both an appropriate cell counter and blood film examination is useful for differentiating inherited macrothrombocytopenias from ITP.
Noris
P
P
Department of Internal Medicine, University of Pavia, Pavia, Italy. p.noris@smatteo.pv.it
Klersy
C
C
Zecca
M
M
Arcaini
L
L
Pecci
A
A
Melazzini
F
F
Terulla
V
V
Bozzi
V
V
Ambaglio
C
C
Passamonti
F
F
Locatelli
F
F
Balduini
C L
CL
D001606:Bernard-Soulier Syndrome / Q000175:diagnosis / Q000473:pathology; D025861:Blood Coagulation Disorders, Inherited / Q000175:diagnosis / Q000473:pathology; D001792:Blood Platelets / Q000473:pathology*; D048429:Cell Size; D003581:Cytodiagnosis / Q000379:methods; D003937:Diagnosis, Differential; D006801:Humans; D020409:Molecular Motor Proteins; D018995:Myosin Heavy Chains; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000175:diagnosis / Q000473:pathology; D013921:Thrombocytopenia / Q000175:diagnosis / Q000473:pathology*
C103814:MYH9 protein, human; D020409:Molecular Motor Proteins; D018995:Myosin Heavy Chains