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Nephrotic-range proteinuria is a condition in which a patient is abnormally excreting excessive amounts of protein in the urine. It can either be associated with nephrotic syndrome, or can be an isolated finding noted on routine analysis of the urine. Symptoms of the condition can include frothy urine, generalized swelling, and blood clots. Diagnosing this condition requires studying the urine to determine exactly how much protein is being lost over time. A number of disorders, including diabetes mellitus and systemic lupus erythematosus, can cause nephrotic-range proteinuria.
Proteinuria is a medical term used to describe protein being excreted in the urine. High levels of protein in the urine are found with nephrotic syndrome, which is a condition caused by kidney dysfunction that is also associated with high blood pressure, high blood cholesterol, low blood protein levels, and decreased renal function. When patients are found to have an amount of protein in the urine that would meet the criteria for nephrotic syndrome, they are said to have nephrotic-range proteinuria. Finding out whether they actually suffer from nephrotic syndrome would require further workup.
Symptoms of nephrotic-range proteinuria vary, but can encompass a number of different aspects of the body’s function. Many patients who have a high concentration of protein in their urine note that the urine appears frothy. The loss of protein in the urine can also cause a number of symptoms. Loss of albumin, a protein that is important in maintaining the right amount of fluid in the blood, can cause swelling of the legs, face, and arms. In addition, sometimes proteins important in preventing the blood from clotting are abnormally excreted in the urine, putting patients at risk for blood clots.
Diagnosis of nephrotic-range proteinuria relies on doing a number of laboratory studies on the urine. Often the first test done is a urinalysis, which can indicate whether or not protein is present in the urine. It does not quantify exactly how much protein is being lost over time, however. In order to determine the amount of protein lost in the urine, all of the urine produced over a 24 hour period can be collected, and the amount of protein in this fluid can be measured. Alternatively, calculating the ratio of protein to creatinine, a specific type of protein, can approximate the degree of protein being lost in the urine.
A variety of different medical conditions can cause nephrotic-range proteinuria. Some of these, such as minimal change disease, focal segmental glomerulosclerosis, and membranous glomerulonephritis are primarily diseases of the kidneys. In other cases systemic diseases can be associated with protein in the urine. Examples include systemic lupus erythematosus, amyloidosis, diabetes mellitus, and multiple myeloma.