Nephrotic Syndrome Workup
- Author: Eric P Cohen, MD; Chief Editor: Vecihi Batuman, MD, FACP, FASN more...
Approach Considerations
Diagnostic studies for nephrotic syndrome may include the following:
- Urinalysis
- Urine sediment examination
- Urinary protein measurement
- Serum albumin
- Serologic studies for infection and immune abnormalities
- Renal ultrasonography
- Renal biopsy
In infants with nephrotic syndrome, genetic testing for the NPHS1 and NPHS2 mutations may be useful. These are mutations of nephrin and podocin, respectively. In children with steroid-resistant nephrotic syndrome, testing for the NPHS2 mutation may be indicated.
Future studies for urinary biomarkers by which the cause and severity of nephrotic syndrome may be identified may become available.[29]
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.[30] 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.
Renal Biopsy
For childhood nephrotic syndrome, a renal biopsy is indicated for the following:
- Congenital nephrotic syndrome
- Children older than 8 years at onset
- Steroid resistance
- Frequent relapses or steroid dependency
- Significant nephritic manifestations
Adult nephrotic syndrome of unknown origin may require a renal biopsy for diagnosis. Adult nephrotic syndrome of unknown origin may require a renal biopsy for diagnosis. Reaching a pathological diagnosis is important because minimal-change disease, focal glomerulosclerosis, and membranous nephropathy have different treatment options and prognoses. It is important to differentiate minimal-change disease presenting in adults from focal glomerulosclerosis, as the former has an excellent response to steroids. Another entity called immunoglobulin M (IgM) nephropathy falls in between the 2 and has an intermediate response to steroids.
A renal biopsy is not indicated in adults with nephrotic syndrome from an obvious cause. For example, in a patient with longstanding diabetes and diabetic retinopathy, the nephrotic syndrome is likely to be secondary to diabetic nephropathy, so kidney biopsy may be unnecessary. However, it is important to not assume diabetic nephropathy as the causative factor for nephrotic syndrome in all diabetic persons. A duration of diabetes of less than 5 years and the absence of retinopathy could be clues to nondiabetic kidney disease.
Other Studies
Serum albumin
The serum albumin level is classically low in nephrotic syndrome, being below its normal range of 3.5-4.5 g/dL. In a single-center study of patients who underwent kidney biopsy for idiopathic proteinuria, Gupta et al found that the frequency of focal and segmental glomerulosclerosis increased with elevations in serum albumin, from 26% in patients with serum albumin < 30 g/L to 74% in patients with serum albumin of 35 g/L or higher.[31]
Serologic studies
In adults with nephrotic syndrome, tests for hepatitis B and C, HIV, and even syphilis may be useful. Tests for lupus, including antinuclear antibody (ANA), anti–double stranded DNA (anti-dsDNA) antibodies, and complement, may be useful. Testing for antineutrophil cytoplasmic antibodies (ANCA) is not indicated in typical nephrotic syndrome, because that test is associated with rapidly progressive glomerulonephritis, which presents with a nephritic picture rather than one that is typically nephrotic.
Tests for previous streptococcal infection, such as antistreptolysin O, are not usually indicated for nephrotic syndrome, since postinfectious glomerulonephritis usually causes a nephritic rather than a nephrotic syndrome.
Ultrasonography
Ultrasonographic scanning can be used to determine whether a patient possesses 2 kidneys and to demonstrate their echogenicity. Individuals with a single kidney may be prone to developing focal glomerulosclerosis. Having only 1 kidney is also a relative contraindication to kidney biopsy. Increased renal echogenicity by ultrasonography is consistent with intrarenal fibrosis, ie, chronic disease with reduced kidney function.
Histologic findings
Histologic findings in nephrotic syndrome are determined by the disease's cause. It is worth noting that in clinical experience, glomerular disease has been found to cause of nephrotic-range proteinuria, not tubular disease. This appears to contradict the proposal that tubular function determines proteinuria.[3]
There are histopathologic stages for membranous nephropathy but not for other causes of nephrotic syndrome.
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