Evaluation of a Technic for Counting Dog and Human Platelets

1. The addition of Na₂EDTA (2.5 to 5 mg./2 ml. of whole blood) to dog or human blood samples has been shown to eliminate the problem of platelet clumping and to provide satisfactory samples for use in enumeration of blood platelets. The statistical errors of platelet counts in blood samples prepared with Na₂EDTA agree well with previously published results obtained with unmodified technic. In blood samples prepared without Na₂EDTA, where clumping is appreciable, the field error is inflated.

2. Variation in the time during which the platelets are permitted to settle in the chamber before counting, between limits of 30 and 90 minutes, has no effect on the count.

3. The period of standing of the diluted blood in 1 per cent ammonium oxalate, from 30 minutes to four hours, appears to have no effect on the out-come of the platelet counting results when the platelets are not clumped.