Proteinuria is the presence of excess in the urine. In healthy persons, urine contains very little protein, less than 150 mg/day; an excess is suggestive of illness. Excess protein in the urine often causes the urine to become foamy (although this symptom may also be caused by other conditions). Severe proteinuria can cause nephrotic syndrome in which there is worsening swelling of the body.
Signs and symptoms
Proteinuria often causes no symptoms and it may only be discovered incidentally.
Foamy urine is considered a cardinal sign of proteinuria, but only a third of people with foamy urine have proteinuria as the underlying cause.[ Retrieved 20 January 2007] or drugs such as pyridium.
Causes
There are three main mechanisms to cause proteinuria:
Proteinuria can also be caused by certain biological agents, such as bevacizumab (Avastin) used in cancer treatment. Excessive fluid intake (drinking in excess of 4 litres of water per day) is another cause.
Conditions with proteinuria
Proteinuria may be a feature of the following conditions:
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Nephrotic syndromes (i.e. intrinsic kidney failure)
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Pre-eclampsia
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Eclampsia
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Toxic lesions of
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Amyloidosis
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Collagen vascular diseases (e.g. systemic lupus erythematosus)
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Dehydration
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Glomerular diseases, such as membranous glomerulonephritis, focal segmental glomerulonephritis, minimal change disease (lipoid nephrosis)
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Strenuous exercise
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Stress
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Benign orthostatic (postural) proteinuria
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Focal segmental glomerulosclerosis (FSGS)
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IgA nephropathy (i.e. Berger's disease)
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IgM nephropathy
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Membranoproliferative glomerulonephritis
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Membranous nephropathy
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Minimal change disease
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Sarcoidosis
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Alport syndrome
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Diabetes mellitus (diabetic nephropathy)
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Drugs (e.g. NSAIDs, nicotine, penicillamine, lithium carbonate, gold and other heavy metals, ACE inhibitors, antibiotics, or opiates (especially heroin)
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Fabry disease
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Infections (e.g. HIV, syphilis, hepatitis, poststreptococcal infection, urinary schistosomiasis)
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Aminoaciduria
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Fanconi syndrome in association with Wilson disease
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Hypertensive nephrosclerosis
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Interstitial nephritis
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Sickle cell disease
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Hemoglobinuria
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Multiple myeloma
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Myoglobinuria
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Organ rejection:
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Ebola virus disease
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Nail–patella syndrome
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Familial Mediterranean fever
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HELLP syndrome
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Systemic lupus erythematosus
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Granulomatosis with polyangiitis
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Rheumatoid arthritis
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Glycogen storage disease type 1
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Goodpasture syndrome
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Henoch–Schönlein purpura
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A urinary tract infection which has spread to the kidney(s)
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Sjögren syndrome
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Post-infectious glomerulonephritis
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Living kidney donor
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Polycystic kidney disease
Bence–Jones proteinuria
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Amyloidosis
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Pre-malignant plasma cell dyscrasias:
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Monoclonal gammopathy of undetermined significance
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Smoldering multiple myeloma
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Malignant plasma cell dyscrasias
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Other malignancies
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Chronic lymphocytic leukemia
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Rare cases of other Lymphoid leukemias
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Rare cases of
Pathophysiology
Protein is the building block of all living organisms.
When kidneys are functioning properly by filtering the blood, they distinguish the proteins from the wastes which were previously present together in the blood.
Thereafter, kidneys retain or reabsorb the filtered proteins and return them to the circulating blood while removing wastes by excreting them in the urine.
Whenever the kidney is compromised, their ability to filter the blood by differentiating protein from the waste, or retaining the filtered protein then returning which back to the body, is damaged.
As a result, there is a significant amount of protein to be discharged along with waste in the urine that makes the concentration of proteins in urine high enough to be detected by medical machine.
Medical testing equipment has improved over time, and as a result tests are better able to detect smaller quantities of protein.
Albumin and immunoglobins
Albumin is a protein produced by the liver which makes up roughly 50%-60% of the total proteins in the blood while the other 40%-50% are proteins other than albumin, such as immunoglobins.
This is why
albuminuria is one of the single sensitive indicators of kidney disease, particularly for those with diabetes or hypertension, compared to routine proteinuria examination.
As the loss of proteins from the body progresses, the suffering will gradually become symptomatic.
The exception applies to the scenario when there's an overproduction of proteins in the body, in which the kidney is not to blame.
Diagnosis
|
|
Daily |
| |
| Less than 0.5 g/day |
| 0.5–1 g/day |
| 1–2 g/day |
| More than 2 g/day |
Conventionally, proteinuria is diagnosed by a simple dipstick test, although it is possible for the test to give a false negative reading,
even with nephrotic range proteinuria if the urine is dilute.
False negatives may also occur if the protein in the urine is composed mainly of
or Bence Jones proteins because the reagent on the test strips,
bromophenol blue, is highly specific for albumin.
[ Retrieved 20 January 2007] Traditionally, dipstick protein tests would be quantified by measuring the total quantity of protein in a 24-hour urine collection test, and abnormal globulins by specific requests for protein electrophoresis.
[ Retrieved 20 January 2007]
More recently developed technology detects human serum albumin (HSA) through the use of (LCs). The presence of HSA molecules disrupts the LCs supported on the AHSA-decorated slides thereby producing bright optical signals which are easily distinguishable. Using this assay, concentrations of HSA as low as 15 μg/mL can be detected.
Alternatively, the concentration of protein in the urine may be compared to the creatinine level in a spot urine sample. This is termed the protein/creatinine ratio. The 2005 UK Chronic Kidney Disease guidelines state that protein/creatinine ratio is a better test than 24-hour urinary protein measurement. Proteinuria is defined as a protein/creatinine ratio greater than 45 mg/mmol (which is equivalent to Microalbuminuria of greater than 30 mg/mmol or approximately 300 mg/g) with very high levels of proteinuria having a ratio greater than 100 mg/mmol.[ – see Guideline 4 Confirmation of proteinuria, on page 9]
Protein dipstick measurements should not be confused with the amount of protein detected on a test for microalbuminuria which denotes values for protein for urine in mg/day versus urine protein dipstick values which denote values for protein in mg/dL. That is, there is a basal level of proteinuria that can occur below 30 mg/day which is considered non-pathology. Values between 30 and 300 mg/day are termed microalbuminuria which is considered pathologic.
Analysis
It is possible to analyze urine samples in determining
albumin,
hemoglobin and
myoglobin with an optimized MEKC method.
Treatment
The most common cause is diabetic nephropathy; in this case, proper glycemic control may slow the progression. Medical management consists of angiotensin converting enzyme (ACE) inhibitors, which are typically first-line therapy for proteinuria. In patients whose proteinuria is not controlled with ACE inhibitors, the addition of an aldosterone antagonist (i.e.,
spironolactone)
or angiotensin receptor blocker (ARB)
may further reduce protein loss.
Atrasentan (Vanrafia) was approved for medical use in the United States in April 2025.
See also
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List of terms associated with diabetes
External links
