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The automated platelet evaluation is a fundamental component of
the CBC and is used to diagnose and monitor platelet disorders,
including thrombocytopenia and abnormalities and variability in the
size of platelets. It is essential to obtain accurate platelet counts for
diagnostic and therapeutic purposes, but the accuracy of automated
platelet counts can be affected by platelet clumping,
which will decrease reported counts since clumps of platelets will not
be counted with any automated (in-house or reference
laboratory) hematology analyzers. Unrecognized falsely decreased platelet counts
(pseudothrombocytopenia) can have devastating consequences for
patient care, including costly ancillary diagnostics, as well as potentially
unnecessary medications and treatments.
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It is for this reason that every low platelet count detected by any
hematology analyzer must be verified by a blood film microscopic
examination. It should take less than 30 seconds total time to determine
if the low platelet count is a true thrombocytopenia or an artifact due to
analyzer and/or sample collection issues.
 
One can quickly and easily detect platelet clumps by examining the
feathered edge of the blood film. In most situations, the clumps of
platelets will collect along with any other large components of the
blood. In addition, in the monolayer of the blood film, you should see
a minimum of 8 to 10 platelets per 100x oil objective field of view when
thrombocytopenia is not present. A crude estimate of platelet numbers
can be determined when there is no clumping by multiplying the
average number of platelets observed in a 100x oil objective field of
view by 20,000. Although not as precise as an automated count, this
method gives an approximate guide to the platelet count and should
roughly correlate with the analyzer count. While impossible to accurately
determine the platelet count when platelet clumping is noted on a blood
film, it is usually assumed that the platelet count is likely to be adequate
if platelet clumping is present. For a more precise determination, an
additional blood sample may be necessary.
References:
Reagan W, Sanders T, DeNicola D. Veterinary Hematology Atlas of Common Domestic Species.
Ames, Ia: Blackwell Publishing; 1998.
Thrall MA, et al. Veterinary Hematology and Clinical Chemistry. Philadelphia, Pa: Lippincott,
Williams & Wilkins; 2004.
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