The analytic basis for the use of platelet estimates from peripheral blood smears. Laboratory and clinical applications.

Estimation of the platelet count from examination of peripheral blood smears is a widely practiced procedure, but statistical validity to judge the accuracy of the technic has been lacking. More than 400 patients' platelet estimates and counts were analyzed to develop a simple working formula to permit a reasonably accurate platelet estimate. Smear-to-smear and technician-to-technician variabilities were defined, and the influences of different microscopes on the platelet estimates were demonstrated. Platelet estimates can be used as a rapid, convenient measurement suitable for providing useful information for clinical judgement of a patient's platelet status providing that the method's limitations are recognized.