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To the Editor:—
I would like to call attention to an erroneous statement found in "Estimation of Total Circulating Sodium," by C. M. Leevy and F. J. Donovan (J. A. M. A.159:771 [Oct. 22] 1955). The authors state: "The total circulating sodium is usually low in uncomplicated salt depletion in contrast to a normal level in sodium redistribution." In conditions such as hypopotassemia, where a shift of sodium into the cells may occur, serum sodium level multiplied by plasma volume will obviously give a low, rather than a normal, value. This, of course, is not total circulating sodium but total circulating extracellular sodium. The intracellular compartment may contain as high as 37 mEq. per liter of sodium. Estimates of total sodium utilizing radiosodium, while more accurate than the method described by the authors, may be inaccurate in pathological states due to the long time required for the tracer
Clarkin JR. CIRCULATING SODIUM ESTIMATION. JAMA. 1956;161(3):270. doi:10.1001/jama.1956.02970030088025