Protein in Urine

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Urine protein testing is used to detect protein in the urine, to help evaluate and monitor kidney function, and to help detect and diagnose early kidney damage and disorder. A semi-quanititative test such as a dipstick urine protein is used to screen the general population for the presence of protein in the urine as part of a routine urinalysis. If slight to moderate amounts of protein are detected, then a repeat urinalysis and dipstick protein may be performed at a later time to see if there is still protein in the urine or if it has dropped back to undetectable levels. If there is a large amount of protein in the first sample and/or the protein persists in the second sample, then a 24-hour urine protein may be used as a follow-up test. Since the dipstick primarily measures albumin, the 24-hour urine protein test also may be ordered if a doctor suspects that proteins other than albumin are being released.

The urine protein test tells the doctor that protein is present in the urine, but it does not indicate which types are present or the cause of the proteinuria. When a doctor is investigating the reason, he also may order a serum and urine protein electrophoresis test to determine which proteins are being excreted and in what quantities. This is especially true if he suspects abnormal protein production, such as with multiple myeloma. He may order a Comprehensive Metabolic Panel (CMP) to look at albumin and total protein levels in the blood and to help evaluate kidney and liver function. If kidney disorder or damage is suspected, he may also may imaging scans to evaluate the appearance of the organ.

Proteins may be measured with the Albustix Test. Since proteins are very large molecules (macromolecules), they are not normally present in measurable amounts in the glomerular filtrate or in the urine. The detection of proteins in your urine may indicate that the permeability[disambiguation needed] of the glomerulus is abnormally increased. This may be caused by renal infections or it may be caused by other disorders that have secondarily affected the kidneys such as diabetes mellitus, jaundice, or hyperthyroidism.

Dipstick screening for protein is done on whole urine, but semi-quantitative tests for urine protein should be performed on the supernatant of centrifuged urine since the cells suspended in normal urine can produce a falsely high estimation of protein. Normally, only small plasma proteins filtered at the glomerulus are reabsorbed by the renal tubule. However, a small amount of filtered plasma proteins and protein secreted by the nephron (Tamm-Horsfall protein) can be found in normal urine. Normal total protein excretion does not usually exceed 150 mg/24 hours or 10 mg/100 ml in any single specimen. More than 150 mg/day is defined as proteinuria. Proteinuria > 3.5 gm/24 hours is severe and known as nephrotic syndrome.

Dipsticks detect protein by production of color with an indicator dye, Bromphenol blue, which is most sensitive to albumin but detects globulins and Bence-Jones protein poorly. Precipitation by heat is a better semiquantitative method, but overall, it is not a highly sensitive test. The sulfosalicylic acid test is a more sensitive precipitation test. It can detect albumin, globulins, and Bence-Jones protein at low concentrations.

A dipstick urine protein is measured frequently as a screening test, whenever a urinalysis is performed. This may be done as part of a routine physical, a pregnancy workup, when a urinary tract infection is suspected, as part of a hospital admission, or whenever the doctor wants to evaluate kidney function. It may also be done when a previous dipstick has been positive for protein to see if the protein excretion persists.

A 24-hour urine protein may be ordered as a follow-up test when the dipstick test shows that there is a large quantity of protein present in the urine or when protein is shown to be persistently present. Since the dipstick primarily measures albumin, the doctor may order a 24-hour urine protein test even when there is little protein detected on the dipstick if he suspects that there may be proteins other than albumin being released.

When a doctor is diagnosing the cause of proteinuria, he also may order a urine protein electrophoresis test to determine exactly which proteins are being excreted and in what quantities. A serum protein electrophoresis may also be ordered to look at the proteins in the blood, especially when abnormal protein production is suspected. Other blood tests, such as a Blood Urea Nitrogen (BUN) and creatinine, may be ordered to evaluate kidney function and an albumin and/or total protein test may be performed to look at the proteins in the blood.

Test results
Protein in the urine is a warning sign. It may indicate kidney damage or disorder or it may be a transient elevation due to an infection, medication, vigorous exercise, or emotional or physical stress. In some people, it may be present during the day and absent at night when the patient is lying down (orthostatic proteinuria). In pregnant women, elevated urine protein levels can be associated with preeclampsia.
When kidney damage is present, the amount of protein present is generally associated with the severity of damage, and increasing amounts of protein over time indicate increasing damage and decreasing kidney function. Proteinuria is associated with many disorders and conditions, including:
·Amyloidosis  
·Bladder cancer  
·Congestive heart failure  
·Diabetes  
·Drug therapies that are potentially toxic to the kidneys  
·Glomerulonephritis  
·Goodpasture's syndrome  
·Heavy metal poisoning  
·Hypertension  
·Kidney infection  
·Multiple myeloma  
·Polycystic kidney disorder  
·Systemic lupus erythematosus  
·Urinary tract infection  

Also you should know
The different methods of detecting protein in the urine vary in performance. For example, a positive dipstick protein may be elevated due to other sources of protein, such as blood, semen, or vaginal secretions in the urine. Since it measures primarily albumin, the dipstick may occasionally be normal when significant quantities of other proteins are present in the urine. A 24-hour urine sample gives the protein excretion rate over 24 hours. It will be accurate only if all of the urine is collected. The protein to creatinine ratio is more of a snapshot of how much protein is in the urine at the time the sample is collected. If it is elevated, then protein is present; if it is negative, it is possible that the patient was just not excreting measurable amounts of protein at that time.

Kidney damage does not go away. The goal is to detect kidney disorder and damage early to minimize the damage and prolong kidney function. If the proteinuria detected is due to a kidney infection or urinary tract infection, the kidneys frequently will return to normal function as the infection resolves. If it is due to a medication, then in most cases the kidneys are likely to return to normal or near normal function when the medication is stopped.



 
 
 
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All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.