Common conditions such as fever, congestive heart failure, seizure activity, pancreatitis, and exercise are frequently associated with transient proteinuria. Stimulation of the renin-angiotensin system has been suggested as a putative cause. The proteinuria resolves with treatment of the underlying illness. Orthostatic proteinuria occurs in up to five percent of adolescents but is uncommon in older age groups. Typically, such patients demonstrate proteinuria while in the upright position.
Orthostatic proteinuria resolves when the recumbent position is assumed.
Persistent proteinuria, in contrast, generally connotes significant renal pathophysiology and can be categorized as overflow, glomerular, or tubulointerstitial in nature. The smaller and more positively charged a protein, such as globulin, the greater its filtration into the urinary space. Conversely, the larger and more negatively charged a protein, such as albumin, the less filtration it undergoes. Over 90 percent of this filtered load is reabsorbed by the tubule, so that 150 mg of protein is maximally excreted each day. In overflow proteinuria, normally filtered proteins are overproduced and overwhelm the reabsorptive capacity of the tubule.