Filter bleeding time: a new in vitro test of hemostasis. I. Evaluation in normal and thrombocytopenic subjects

Disadvantages of current bleeding time methods include poor reproducibility, limited repeatability, and at times scar formation. We report a new, in vitro technique which circumvents these problems. Venous blood is collected in sodium citrate, stored capped in a siliconized tube at 37 degrees C until use, and made to flow under constant pressure through a filter of Woven Dacron. Flow rate progressively falls as platelet aggregates occlude the filter, as verified by scanning electron microscopy and 111Indium-labeled platelet radioactivity of the filter. Filter bleeding time (FBT) was 4.33 +/- 1.79 (means x +/- SD) min in 23 healthy human volunteers and 3.08 +/- 1.08 min in 14 normal dogs. Bleeding volume (BV) (number of drops) was 29 +/- 12 in the humans and 16 +/- 6 in the dogs. Initial bleeding rate (IBR) (number of drops during first minute) was 14 +/- 3 in citrated blood and 25 +/- 5 drops/min in EDTA blood of the humans (P = 9 X 10(-10)), 8 +/- 2 in citrated blood and 14 +/- 6 drops/min in EDTA blood of the dogs (P = .0004). Percent platelet reduction during passage of blood through the filter (PCR) was 27.5 +/- 7.2 in citrated blood and 4.9 +/- 2.6 in EDTA blood of the humans (P = 2 X 10(-12)), while in dogs it was 25.7 +/- 8.3 in citrated blood and 5.3 +/- 4.2 in EDTA blood (P = 8 X 10(-7)). The results of these parameters using human platelet rich plasmas (PRPs) were similar to those with human whole blood, but significant decrease of drop rate was not observed in canine PRPs during passage of PRP through the filter. FBT, BV, and IBR were correlated (r = -0.91, -0.84 and -0.62 respectively) with platelet count in 12 specimens obtained from 4 dogs in which thrombocytopenia (107 to 4 X 10(3) platelets/microliter) was induced by estradiol. This new test is unaffected by specimen transport by pneumatic tube, is sensitive to platelets, and should be useful for analysis of both quantitative and qualitative platelet abnormalities in man.