How is plasma volume measured in the evaluation of secondary polycythemia?

Updated: Jul 20, 2020
  • Author: Srikanth Nagalla, MBBS, MS, FACP; Chief Editor: Sara J Grethlein, MD, FACP  more...
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Answer

To measure plasma volume, use radiolabeled albumin (iodine-131 [131 I]), similar to the process used with the red blood cell mass measurement. Plasma volume can also be calculated indirectly using total red blood cell mass and the hematocrit value.

Decreased plasma volume with a normal red blood cell mass indicates a relative polycythemia or erythrocytosis, similar to the increased hemoglobin and hematocrit levels associated with severe dehydration. Decreased plasma volume due to dehydration is the most common cause of elevated hemoglobin or hematocrit levels in the general population.


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