genitourinary disorders
Proteinuria
Pathophysiology of Proteinuria
Although the glomerular basement membrane is a very effective barrier against larger molecules (eg, most plasma proteins, primarilyalbumin), a small amount of protein passes through the capillary basement membranes into the glomerular filtrate. Some of this filtered protein is degraded and reabsorbed by the proximal tubules, but some is excreted in the urine. The upper limit of normal urinary protein excretion is considered to be 150 mg/day, which can be measured in a 24-hour urine collection or estimated by random urine protein/creatinine ratio (values>0.3 are abnormal); foralbuminit is about 30 mg/day.Albuminexcretion between 30 and 300 mg/day (20 to 200 mcg/min) is considered moderately increased albuminuria (microalbuminuria), and higher levels are considered severely increased albuminuria per new terminology. Mechanisms of proteinuria may be categorized as Glomerular Tubular Overflow Functional Glomerular proteinuriaresults from glomerular disorders, which typically involve increased glomerular permeability; this permeability allows increased amounts of plasma proteins (sometimes very large amounts) to pass into the filtrate. results from renal Overview of Tubulointerstitial Diseases that impair reabsorption of protein by the proximal tubule, causing proteinuria (mostly from smaller proteins such as immunoglobulin light chains rather than Overflow proteinuriaoccurs when excessive amounts of small plasma proteins (eg, immunoglobulin light chains produced in multiple myeloma) exceed the reabsorptive capacity of the proximal tubules. Functional proteinuriaoccurs when increased renal blood flow (eg, due to exercise, fever, high-output heart failure) delivers increased amounts of protein to the nephron, resulting in increased protein in the urine (usually<1 g/day). Functional proteinuria reverses when renal blood flow returns to normal. Orthostatic proteinuriais a benign condition (most common among children and adolescents) in which proteinuria occurs mainly when the patient is upright. Thus, urine typically contains more protein during waking hours (when people are more often upright) than during sleep. It has a very good prognosis and requires no special intervention. Proteinuria caused by renal disorders usually is persistent (ie, present on serial testing) and, when in the nephrotic range, can cause significant protein wasting. Presence of protein in the urine is toxic to the kidneys and causes renal damage. 