Postural pseudoanemia: posture-dependent change in hematocrit.
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).
Jacob
Giris
G
Jacob Recanati Autonomic Dysfunction Center, Internal Medicine C, Rambam Medical Center, Haifa, Israel.
Raj
Satish R
SR
Ketch
Terry
T
Pavlin
Boris
B
Biaggioni
Italo
I
Ertl
Andrew C
AC
Robertson
David
D
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
D004396:Coloring Agents; D019275:Radiopharmaceuticals; D012711:Serum Albumin, Radio-Iodinated; D005070:Evans Blue