Consequences of iron deficiency may include stroke and myocardial ischemia,S3.16-4 S3.16-6 although published findings are inconsistent. Iron deficiency requires assess- ment of serum iron, ferritin, and transferrin levels, be- cause mean corpuscular volume is not a reliable screen- Limited data suggest that treatment of transferrin saturation <20% with iron supplementation until iron stores are replete can be done safely.S3.16-8 Although there is an exponential relationship be- tween viscosity and hematocrit, available data do not justify a cut point for a safe hematocrit.S3.16-3 There is no clear correlation between viscosity, iron deficiency, and a patient s symptoms or clinical condition.S3.16-3 The nature and cause of hyperviscosity symptoms are not well understood. The severity and frequency of symp- toms of hyperviscosity do not correlate with measured hematocrit. Phlebotomy is, therefore, rarely necessary in patients with secondary erythrocytosis, and routine phlebotomy is not supported by data. Patients with suspected hyperviscosity need to be rehydrated either CLINICAL STATEMENTS AND GUIDELINES with oral fluids or intravenous normal saline solution as a first-line therapy, evaluated for iron deficiency, and treated if appropriate. Phlebotomy (with equal volume fluid replacement) is sometimes performed in special cases wherein, after adequate hydration, hematocrit remains higher than the patient s baseline and symp- toms persist, or there is evidence of end-organ damage attributable to hyperviscosity (eg, myocardial ischemia, transient ischemic attack/stroke).S3.16-9,S3.16-10 Observational studies in cyanotic individuals have shown evidence of altered synthesis and function of clotting factors that may contribute to both hypo- and and thrombosis and bleeding (particularly epistaxis or hemoptysis) have been described in patients with Eisenmenger syndrome, which may be life-threatening.S3.16-13 S3.16-15 These dispa- rate trends preclude developing universally applicable recommendations, including use of antiplatelet or an- ticoagulant therapy in these patients.S3.16-16 Similarly, there is not a clear role for preoperative phlebotomy to improve coagulation properties. 