Reduced hematocrit level upon splenectomy. Hematocrit measurements were performed in wt mice, untreated tg mice, and splenectomized tg animals that were 114 ± 8 days old, 119 ± 8 days old, and 121 ± 10 days old, respectively, when the hematocrit level was determined. Splenectomy was performed 6 to 7 weeks earlier. The hematocrit level was increased 2-fold in tg mice (0.86 ± 0.06) compared with wt mice (0.42 ± 0.04; P < .01). Six to 7 weeks after splenectomy, the hematocrit level in tg mice was 0.62, which is 31% lower (P < .01) but still significantly 50% higher than that in wt mice (P < .01).