Urine Studies

Urinalysis

Urinalysis is the first test used in the diagnosis of nephrotic syndrome. Nephrotic range proteinuria will be apparent by 3+ or 4+ readings on the dipstick, or by semiquantitative testing by sulfosalicylic acid. A 3+ reading represents 300 mg/dL of urinary protein or more, which is 3 g/L or more and thus in the nephrotic range. The chemistry of the dipsticks is such that albumin is the major protein that is tested.Glucosuria points to diabetes.

Urine sediment examination

The urine sediment exam may show cells and/or casts.Waxy casts mark proteinuric renal disease. By use of a polarizing microscope, one can see oval fat bodies and also fatty casts. These point to the nephrotic syndrome. They occur because of glomerular filtration of lipoproteins, the uptake of these by the tubular cells that then fall off into the urine. Viewed by polarizer, the oval fat bodies and fatty casts cause a "Maltese cross" appearance.The presence of more than 2 red blood cells (RBCs) per high power field is indicative of microhematuria. Microhematuria may occur in membranous nephropathy but not in minimal-change nephropathy.Glomerular disease may allow RBCs to traverse the damaged glomerular basement membrane, and the RBCs in the sediment may then be deformed, or dysmorphic. This points to glomerular disease with inflammation and destruction of the normal structures (ie, a nephritis, and thus a nephritic picture, with hematuria, oliguria, azotemia, and hypertension). This could occur in, for example, nephrotic syndromes associated with IgA nephropathy or proliferative glomerulonephritis.More than 2 granular casts in the entire sediment is a biomarker for renal parenchymal disease. Variable-caliber granular casts point to reduced renal function.

Urinary protein measurement

Urinary protein is measured by a timed collection or a single spot collection.A timed collection is typically done over a 24-hour period, starting at 7 am and finishing the next day at the same time. In healthy individuals, there are no more than 150 mg of total protein in a 24-hour urine collection.

A single spot urine collection is much easier to obtain. When the ratio of urine protein to urine creatinine is greater than 2 g/g, this corresponds to 3 g of urine protein per day or more.The exact type of urine protein is of potential interest. This can be tested by urine protein electrophoresis.

Proteinuria that does not include albumin may point to overflow proteinuria that occurs in paraproteinemias, such as multiple myeloma.There has been intermittent interest in establishing whether proteinuria is "selective" for albumin (ie, > 85% albumin), as opposed to nonselective. In the case of selective proteinuria, there could be a charge-selective leak of albumin across the glomerular barrier, perhaps due to reduced negative charges on that barrier, whereas nonselective proteinurias would point to more substantial glomerular injury and perhaps also to lesser response to prednisone treatment.Serum tests for kidney function are essential.

Serum creatinine will be in the normal range in uncomplicated nephrotic syndrome, such as that occurring in minimal-change nephropathy. In children, the serum creatinine level will be lower than it is in adults. The normal adult serum creatinine level is approximately 1 mg/dL, whereas that of a child aged 5 years will be about 0.5 mg/dL. Values higher than this indicate reduced kidney function.