![]() Platelets should have normal granularity (note, equine platelets have less obvious granules than other species). The variability of platelet size in cats may be due to genetic variation in the structure of β1-tubulin ( Boudreaux et al 2010). Physiologic: All animals to some extent have large platelets, but this is particularly true of cats, who have a much higher upper reference limit (and broader reference interval) for MPV than other species.This is why blood smears should be examined for platelet clumping to verify any platelet count. Thus clumps will decrease the platelet count and increase the MPV. Platelet clumping: Smaller clumps that fall within the counting size threshold are “seen” as single large platelets by most automated analyzers.Thus platelet counts and the MPV are most valid in freshly collected and analyzed samples. Storage of blood: Platelets activate and swell with storage, particularly at 4☌ (the preferred temperature of storage of EDTA blood for a hemogram).This causes them to look pale and agranular in a blood smear and is helpful for distinguishing between artifactual and other causes of increased platelet volume Artifact: Platelets that are activated either degranulate or imbibe water.Also note, that low numbers of large platelets may not increase the MPV (which represents the mean) above reference intervals. Causes of an increased MPV are given below. An increased MPV, with the presence of large platelets in a blood smear and absence of platelet clumps, in a thrombocytopenic animal is suggestive of a bone marrow response to the thrombocytopenia (a regenerative thrombocytopenia) however the lack of large platelets does not exclude a bone marrow response and large platelets can be present due to abnormal bone marrow production of platelets. The MPV should not be interpreted alone but in conjunction with the platelet count. Method of measurementĪ low MPV is of no diagnostic relevance. Also, there is a substantial degree of variation in platelet size in healthy animals, particularly in some species, such as cats, so identification of large platelets in a thrombocytopenic animal depends on the species, number and appearance of the platelets. Large platelets are generally presumed to be young platelets, however, large size is not synonymous with immaturity. These larger platelets can be observed in blood smears and, if in sufficient number, will increase the MPV above reference intervals. During active thrombopoiesis, larger platelets than normal may be produced (similar to immature anucleate RBC, which are usually larger than mature RBC). The MPV can be useful for distinguishing between causes of thrombocytopenia (just like the MCV can provide guidance as to causes of anemia), but should never be used in isolation. Automated hematologic analyzers (electrical impedance- or laser-based) can measure platelet volume (MPV), just like they can measure red blood cell volume ( MCV). ![]()
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