Page 26 - Clinical Hematology Atlas

10 SECTION ONE INTRODUCTION

the estimate is consistent with a normal platelet count, decreased if below the lower limit
of normal for that laboratory, and increased if above the upper limit of normal. A general
3
9
reference range is 150,000 to 450,000/mm (150–450 3 10 /L). When a patient is ex-
tremely anemic or has erythrocytosis, a more involved formula for platelet estimates may
be used:
B
Average number of platelets/field 3 Total RBC count
200 RBCs/field
The estimate can be compared with an automated platelet count as an additional quality-
control measure. If the estimate and the instrument platelet count do not agree, discrepancies
must be resolved. Some causes for discrepancy include the presence of giant platelets, many
schistocytes, and platelet satellitism. Notably, high-quality 403 or 503 oil immersion objec-
tives can be used by the experienced technologist to perform the differential analysis of the
blood smear. However, all abnormal findings must be verified under the 1003 objective.

SUMMARY
A considerable amount of valuable information can be obtained from properly prepared,
stained, and evaluated peripheral blood smears. Many laboratories use smears made by the
wedge technique from EDTA anticoagulated blood and stained with Wright or Wright-
Giemsa stain. The smears should be evaluated in a systematic manner using first the 103, then
403 high dry or 503 oil, and finally the 1003 oil immersion objectives on the microscope.
WBC differential and morphology and the RBC morphology and platelet estimate are
included in the smear evaluation.