title: Postural pseudoanemia: posture-dependent change in hematocrit.
abstract: OBJECTIVE
  To determine the magnitude of posture-related changes in blood components.
  
  
  METHODS
  Twenty-eight healthy subjects were studied between 1995 and 2004 at the Vanderbilt Autonomic Dysfunction Center, Nashville, Tenn. Lying and standing plasma volume (PV) and hematocrit (Hct) values were determined for each subject.
  
  
  RESULTS
  Individual PV decreases on standing ranged from 6% to 25%. The absolute mean +/- SD PV shift was 417+/-137 mL (range, 149-717 mL). The mean +/- SD change in Hct was from 37.7%+/-2.8% while supine to 41.8%+/-3.2% within 30 minutes of standing. This absolute increase in Hct of 4.1%+/-1.3% represents a relative increase of 11.0%+/-3.6% from lying to standing.
  
  
  CONCLUSIONS
  Changes in posture can lead to substantial changes in Hct, which may be attributed mistakenly to blood loss or acute anemia and result in a cascade of unnecessary diagnostic costs. In reality, these changes represent postural pseudoanemia, a normal physiological response to a change in position from standing to lying (and vice versa).
authors.affiliation: Jacob Recanati Autonomic Dysfunction Center, Internal Medicine C, Rambam Medical Center, Haifa, Israel.
authors.forename: Giris
authors.initials: G
authors.lastname: Jacob
authors.forename: Satish R
authors.initials: SR
authors.lastname: Raj
authors.forename: Terry
authors.initials: T
authors.lastname: Ketch
authors.forename: Boris
authors.initials: B
authors.lastname: Pavlin
authors.forename: Italo
authors.initials: I
authors.lastname: Biaggioni
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Ertl
authors.forename: David
authors.initials: D
authors.lastname: Robertson
mesh_terms: D000328:Adult; D000740:Anemia / Q000097:blood / Q000503:physiopathology*; D004396:Coloring Agents / Q000008:administration & dosage; D005070:Evans Blue / Q000008:administration & dosage; D005260:Female; D005500:Follow-Up Studies; D006400:Hematocrit; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D010953:Plasma Volume / Q000502:physiology; D011187:Posture / Q000502:physiology*; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D012016:Reference Values; D012189:Retrospective Studies; D012711:Serum Albumin, Radio-Iodinated / Q000008:administration & dosage
chemical_list: D004396:Coloring Agents; D019275:Radiopharmaceuticals; D012711:Serum Albumin, Radio-Iodinated; D005070:Evans Blue