High fluorescent platelets fraction in macrothrombocytopenic Norfolk terrier

Idiopathic asymptomatic macrothrombocytopenia is a congenital disorder extensively studied in Cavalier King Charles Spaniels (CKCS) characterized by low platelets number, increase mean platelets volume, and normal plateletcrit. Even if this disorder has no effect on platelets life span, large platelets have high RNA content when analysed by automated haematology analyser with optical method based on fluorescent nucleic acid dye. Recently, we have reported a similar macrothrombocytopenia in a group of related Norfolk terriers (NT). Aim of this work is the evaluation of high fluorescent platelets fraction in asymptomatic macrothrombocytopenic Norfolk terriers and the comparison with thrombocytopenic dogs affected by disorders associated with decreased production or increased destruction of platelets. Blood samples from 10 Norfolk terriers (group 1), 37 thrombocytopenic dogs for bone marrow suppression due to haematopoietic neoplasms (group 2), and 7 dogs with thrombocytopenia due to increased destruction or consumption (group 3) were considered. As a control group, 86 dogs with normal CBC count were included. Samples were analysed with Sysmex XT-2000iV and values of optical platelets count (PLT-O), impedance count (PLT-I), and Delta value (PLT-O/PLT-I x100) were acquired. In the PLT-O scattergram, a gate including normal-sized platelets based on normal dogs and a gate comprising platelets with high fluorescent were drawn. The percentage (HFPF%) and absolute numbers of high fluorescent platelets (HFPF) were recorded. Seven Norfolk terriers had macrothrombocytopenia and 3 had platelet counts comparable with control dogs. PLT-O count of all NT dogs was 144,122 (median 88), PLT-I was 118,157 (median 27.5) with a Delta value of 302,246 (median 242). HFPF% was 2,114 (median 28.3) and HFPF 17,211 (median 16.8).When only thrombocytopenic NT were considered, PLT-O was 70,827,4 (median 82), PLT-I was 21,412,9 (median 16) with Delta of 392,5243 (median 337). HFPF% was 29,46,8 (median 29.9) and HFPF 21,910,1 (median 26.2). Compared to control dogs, all groups had a significant lower PLT-O and PLT-I count (Po.01) with increased Delta value. NT had also significant higher HFPF% and HFPF (Po.01), while group 2 and group 3 had only HFPF% significantly different from healthy dogs (Po.01). Compared to group 2, HFPF% and HFPF in NT were higher (Po.05). When only thrombocytopenic NTwere considered in comparison with group 3, no differences were evident for PLT-O and PLT-I, and HFPF% and HFPF were significant higher (Po.05). As already reported for CKCS, large platelets in NT also showed high RNA content. Even if platelets life span is not affected, the high fluorescent platelets fraction in NT was higher, not only compared to healthy dogs, but also to dogs with decreased platelet production or increased platelet destruction.