Tail bleeding time. Sequential tail bleeding times (BT1 followed by BT2) are shown for 262 Gp6^−/− mice and 28 Gp6^+/+ littermates. In the case of Gp6^−/− mice, 4 categories (A through D) were defined based on the reproducibility of the BT, depicted on the ordinate (in seconds). (A) In 120 mice, both bleeding times reached the maximal limit of 600 seconds and were deliberately stopped by physical pressure to the cut tail area. In 2 mice, the second bleeding time was decreased by no more than 10% relative to the initial bleeding time. These 122 mice were designated Gp6^−/− LONG. (B) In 24 mice, the initial bleeding time of 600 seconds was not confirmed because of a significantly shortened second bleeding time. (C) In 50 mice, the second bleeding time was 600 seconds and significantly higher than the first bleeding time. The mice in categories B and C were excluded from subsequent genetic linkage analyses. (D) In 66 mice, there was excellent reproducibility between the 2 bleeding times, and each mouse had an average time within the range of values obtained for Gp6^+/+ mice. These mice were designated Gp6^−/− SHORT. (E) Consecutive bleeding times for 28 wild-type (Gp6^+/+) littermates (mean ± SD = 114 ± 27 seconds; range = 47-198 seconds).