The importance of recognizing postural pseudoanemia

The determination of the packed red cell volume and the hemoglobin level has been paramount for monitoring anemia and blood loss for patients in the hospital setting. Recently, these variables have been studied during various control conditions including changes in posture. It has been found that the hematocrit changes markedly with alteration of body posture, in such a way that shifts of estimated blood volume of 1 pint can commonly be elicited by a simple change of posture from supine to upright or vice versa. Therefore, it is important to recognize that in addition to the numerous pathological conditions that may affect the value of the packed cell volume, certain physiological maneuvers may have an equal impact and may confound the accurate assessment of true pathological changes in these variables. Thus, changes in posture can lead to substantial changes in hematocrit, which may be attributed mistakenly to blood loss or acute anemia and may 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. This stydy was supported in part by grants from the National Institutes of Health (RR00095, 2PO1 HL55693). The Daxor Corporation provided the Volumex iodine 131-labeled human serum albumin used for plasma volume determination at no cost to the authors. Dr. Jacob was a Merck International Fellow. Dr. Raj is supported by a K23 award from the National Institutes of Health (K23 RR020783-01A1). This work has been previously reported in ref. 1.