Morphology and Enumeration of Human Blood Platelets

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Abstract
Changes in platelet morphology were studied with the aid of the phase microscope. Rapid changes in platelet morphology were observed with all the anticoagulant solns. in common use, as well as with suspension of platelets in normal saline. It was concluded that changes reported in the past as characteristic of platelet behavior during the clotting process must be interpreted with caution because the technics of examination in themselves influence platelet morphology. The observed changes in platelet morphology do not necessarily interfere with the ready identification of platelets as separate blood elements and a satisfactory technique for the counting of platelets was developed. The technic consists in rapid dilution of a sample of venous blood with 1% ammonium oxalate in a red cell pipette, and counting of the diluted sample in a conventional hemocytometer with optically flat bottom, and a No. 1 coverslip, using a 43x phase objective and a long working distance phase condenser. With this technic the platelet count was subject only to those errors inherent in any blood cell count, namely the pipette, chamber and field errors of the count, and platelet counts could be performed routinely with an accuracy comparable to that of the WBC and RBC counts. The 95% range of single counts in 50 healthy males was 140,000 to 440,000 for fresh venous blood, with a mean of 257,000. In oxalated blood the mean was 232,000. The difference was statistically significant. In a series of multiple counts on 10 individuals on 5 successive days, platelet counts varied markedly between individuals, but stayed within narrow limits for any given individual for the period of observation.