Quantitative red cell traits. (A) Distributions of quantitative red cell traits in HHT and control populations: total red blood cell count (left), hematocrit (center), and hemoglobin (right) plotted for the HHT patients (1 measurement per patient, proband, and affected family members from cohorts 1 and 2) above the respective INTERVAL population distribution from 50 000 blood donors (1 result per donor).⁶⁷  Upper panel, males; lower panel, females. Although the median values are similar, it should be noted that HHT cases had a higher proportion of extreme red cell values (both high and low) relative to healthy controls; for red cell count, hematocrit, and hemoglobin, respectively, the proportion of HHT patients within the fifth to 95th sex-stratified percentiles of the INTERVAL ranges were only 66%, 61%, and 50% for males and 64%, 55%, and 48% for females, respectively (all P values <.0001). (B) Relationships with bleeding and hypoxemia in HHT cohort. Patients with more severe blood losses (bleeders) were defined by a bleeding score ≥4 and subcategorized by the presence (purple symbols) or absence (blue symbols) of pulmonary AVMs (PAVMs), which impair gas exchange, resulting in lower arterial partial pressure of oxygen and hence lower SaO₂. Patients with lower bleeding scores were also categorized by the presence (green) and absence (red) of PAVMs. The graphs (upper panel, males; lower panel, females) plot total red blood cell count (left), hematocrit (center), and hemoglobin (right) against same-day SaO₂ measured by finger oximetry for 10 minutes standing using 1 measurement per patient (proband and affected family members). Note that in all 6 analyses, the patients with greater bleeding (red and purple) tended to have lower red blood cell indices (P < .0001 in all cases), and there was a superimposed anticorrelation between the red cell indices and SaO₂ (P < .0001 in all cases). (C) SaO₂ in HHT patients. Histograms of SaO₂ in ACVRL1 and ENG cases. (D) Bleeding score in HHT patients. Histograms of bleeding scores in ACVRL1 and ENG cases.