Platelet activity ratio. A new approach for quantitation of platelet factor 3.

The ratio of kaolin recalcification time in platelet-poor plasma to kaolin recalcification time in platelet-rich plasma appears to provide a more accurate estimate of platelet factor 3 activity than measurement of kaolin recalcification time in platelet-rich plasma alone. This ratio is termed the "platelet activity ratio." Over a fairly wide range the platelet activity ratio appears to follow a linear log-log relationship to platelet count (platelet counts of 12,500 to 200,000). The use of diluted platelet substitute as artificial standard greatly simplifies preparation of (1) standard curves and (2) quality control plasmas. If platelet activity ratio is expressed as a percentage of normal platelet factor 3 activity, the normal range for "total" platelet factor 3 (PF3t) is 60 to 175% and normal range for "available" platelet factor 3 (PF3a) is 14 to 47%.