PATTERNS OF PROTEIN EXCRETION BY THE KIDNEYS

Abstract

The conditioned urine protein excretion test was used in over 4000 hospitalized patients with proteinuria of undetermined origin. This test has proved accurate in differentiating cases with fixed, continuous proteinuria from those with orthostatic (inconstant) and variable proteinuria. Protein excretion by the kidneys is shown to follow simple, regular patterns of distribution: negative, inconstant (orthostatic) and constant or continuous. Continuous excretion of protein indicates significant organic renal disease. The term "orthostatic proteinuria" represents a pathophysiologic disturbance which may be due to a variety of renal disorders, organic and functional. In 15,000 young individuals with proteinuria, 5% were of the continuous and 15% of the orthostatic variety. Most cases (80%) with orthostatic proteinuria persisted, and many were due to demonstrable organic renal disease. Since these renal diseases are progressive, the term "benign proteinuria" is inappropriate. However, in most cases with orthostatic proteinuria no renal lesions could be demonstrated. Considerable quantities of protein may be excreted in orthostatic proteinuria, in some instances as much as in chronic nephritis. Tiselius and paper electrophoresis revealed considerable urine globulin (A/G ratio of 3). Various degrees of severity of orthostatic proteinuria were observed with proteinuria absent in some, only at rest. Persistency of proteinuria and clinical observation suggests that orthostatic proteinuria may be progressive. In this connection, attention is called to frequent instances of obscure continuous proteinuria with normal sediment, usually considered nephritis. The opinion is ventured that some may represent later stages of conditions initially manifested by orthostatic proteinuria.