In the Literature
Vasilatis DM, Walker NJ, Borjesson DL. Amikacin disaggregates platelet clumps in EDTA blood samples from cats and dogs when added postcollection. Vet Clin Pathol. 2023;52(2):228-235. doi:10.1111/vcp.13203
The Research …
Pseudothrombocytopenia from aggregates (ie, clumps) of platelets in EDTA-anticoagulated blood samples analyzed using automated hematology instruments is common in dogs and especially common in cats. Mean platelet volume (MPV) is also inaccurate when platelet aggregates are present because an aggregate may be counted as a single large platelet; high numbers of aggregates can erroneously increase MPV.
Feline platelets cannot be counted accurately with impedance-type hematology analyzers (even without platelet aggregates) because platelets are separated from erythrocytes based on size alone, and the size distribution of feline platelets, which are larger than canine platelets, overlaps with the size distribution of feline erythrocytes, which are smaller than canine erythrocytes. Feline platelets may be accurately counted by flow cytometers that use internal characteristics of platelets in addition to platelet size.
The most common cause of platelet clumps in EDTA-anticoagulated blood samples is aggregation induced by platelet activation during sample collection. Platelet clumping is more often a problem in feline blood samples compared with canine samples, possibly due to greater tissue trauma, time required to collect blood samples, and/or platelet reactivity.
This study evaluated the addition of amikacin for disaggregating platelet clumps in EDTA-containing blood samples collected from 28 cats and 17 dogs (all but one cat had clinical illness). Pseudothrombocytopenia was recognized as platelet clumping on stained blood films prepared prior to the addition of amikacin. Mean platelet counts after amikacin addition increased 134% (from 98.64 × 103/µL to 231.2 × 103/µL) in feline samples and 32% (from 87.53 × 103/µL to 115.6 × 103/µL) in canine samples. Examination of stained blood films after amikacin addition revealed reduced aggregation of platelets, although not complete disaggregation. MPV in feline blood samples was reduced by 14% after amikacin addition but inexplicably increased by 9% in canine samples.
The mechanism by which amikacin disaggregates platelets is unknown, although this study revealed statistically insignificant decreased binding of fibrinogen to platelets; fibrinogen is the principal protein responsible for binding activated platelets together.
Although amikacin had minimal effects (eg, slightly increased mean cell volume) on other CBC and blood film findings, the authors recommend adding amikacin to blood samples only after platelet aggregates are recognized in stained blood films on initial CBC. Potential morphologic effects of amikacin on abnormal blood components, including blood-borne pathogens (eg, hemotropic mycoplasmas), are unknown.
… The Takeaways
Key pearls to put into practice:
Low platelet counts from automated hematology analyzers are common and should be confirmed via examination of stained blood films. Pseudothrombocytopenia can lead to increased expense from potentially unnecessary additional tests and treatments.
Although amikacin addition may not completely eliminate platelet aggregates, the resultant platelet count should be a more accurate reflection of the true platelet count and help with differentiating true thrombocytopenia from pseudothrombocytopenia, especially in cats.
When few or no platelet aggregates are seen on a stained blood film, low platelet count reflects true thrombocytopenia, and a second CBC following amikacin addition is unnecessary.
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