THE RELATIONSHIPS BETWEEN PLASMA SPECIFIC GRAVITY, PLASMA PROTEIN CONTENT AND EDEMA IN NEPHRITIS

Abstract

Conclusions are drawn from 118 observations on 75 nephritic and 9 normal persons. There is a linear relationship between plasma specific gravity and total protein content which holds for blood from both normal and nephritic subjects. Normal plasma with 7 gm. protein per 100 cc. has a specific gravity of approximately 1.027, the gravity of water at the same temperature being taken as 1. With each increase or decrease of 1 gm. protein the sp. gr. rises or falls 0.0029. The relationship between gravity and protein content in nephritic plasma is much closer than that between refractive index and protein content. The presence of non-cardiac edema in most cases of nephritis is closely related to the decrease in total protein content and sp. gr. of the plasma. In the 75 patients examined, who included hemorrhagic, degenerative, and arteriosclerotic types of renal disease, it was found that when the total protein content fell below the lower limit of the range 5.5[plus or minus]0.3%, or the albumin below 2.5 [plus or minus]0.2%, or the specific gravity below 1.0230[plus or minus]0.0003, edema was usually present. When the protein content and sp. gr. were above the upper limits of these ranges edema was usually absent. Exceptions to the usual relationship between plasma protein deficit and edema have been met as follows: (1) During the first weeks of acute hemorrhagic nephritis, and during exacerbations of hemorrhagic nephritis caused by injury or infection, a transient edema may occur when plasma proteins, both total and albumin are above the critical levels previously mentioned. (2) When the plasma globulin content is affected, so that the total protein changes do not parallel albumin changes, total protein content and specific gravity also lose their relationship to edema, the tendency to which appears dependent on albumin rather than on globulin deficit. 3. Salt restriction may cause edema to disappear when total plasma protein and albumin are below the critical levels. Usually, however, when the proteins are below the critical level salt restriction causes only partial disappearance of edema.