Proteinuria

By Silvia German, RN, CNN, Education Manager with the DaVita® National Clinical Education Team

What is proteinuria?

When healthy kidneys filter fluid, minerals and wastes from the blood, they usually do not allow large amounts of serum protein to escape into the urine. But when kidneys aren’t filtering properly, proteinuria can occur, meaning that an abnormal amount of protein is present in the urine.

The two major groups of serum proteins in the blood are albumin and globulins. Albumin is abundant in the blood, accounting for more than 50 percent of all serum proteins. Its important functions include pulling water into capillaries andmaintaining the right amount of water in the circulatory system, as well as binding and carrying substances that are poorly soluble in water. Three examples of these substances are fat soluble vitamins, calcium and some medications.

Globulins are divided into alpha, beta and gamma globulins. Alpha and beta globulins also transport substances, while gamma globulins are known as immunoglobulins or antibodies. Testing for protein in the urine can include all the different proteins or albumin only.

Types of proteinuria

Transient proteinuria is the temporary excretion of protein and can be caused by strenuous exercise, a high fever, exposure to cold, stress and other conditions. Pregnant women may also excrete more protein in their urine. Transient proteinuria does not involve underlying kidney disease and requires no treatment.

Orthostatic proteinuria means an increased amount of protein is excreted when a person is in the upright position. It is most often found in tall, thin adolescents and young adults less than 30 years of age. The kidneys are usually healthy.

Proteinuria can be caused by diseases not involving the kidneys, such as multiple myeloma, a cancer of the plasma cells in the bone marrow. In this case, the blood is flooded with too many proteins that are then filtered into the urine. The condition is known as overflow proteinuria.

The other type of proteinuria is due to kidney disease, such as glomerulonephritis, primary focal segmental glomerulosclerosis (FSGS) or kidney damage due to a systemic disease. Microalbuminuria means low levels of albumin are detected in the urine. Microalbuminuria can indicate that people with diabetes or high blood pressure (hypertension) are developing early stages of kidney disease.

Symptoms of proteinuria

In most cases, proteinuria has no symptoms and is detected during a routine screening in people with high blood pressure or diabetes. If protein loss is severe, nephrotic syndrome may develop. In that case, because of low serum albumin levels, fluid leaks from the circulatory system and collects elsewhere in the body, causing swelling or edema. Edema can be present in the:

  • Face and around the eyes
  • Arms, hands, legs, ankles and feet
  • Abdomen

Other symptoms can include:

  • Foamy urine
  • Weight gain caused by fluid retention
  • Diminished appetite
  • Hypertension

How is proteinuria diagnosed?

Urinalysis covers a number of tests performed on urine, both with special dipsticks and under a microscope. Abnormal presence of cells and urinary casts, tiny tube-shaped particles, may reveal underlying kidney disease.

The Urine Albumin to Creatinine Ratio (UACR) is a test that estimates how much albumin is excreted in a 24-hour period without requiring patients to collect urine for a whole day.

Common proteinuria blood tests check serum creatinine, albumin, cholesterol and blood glucose levels to help determine whether the condition is caused by kidney damage.

If kidney disease is suspected, any of three tests may be conducted:

  • Glomerular filtration rate (GFR): Estimates how much blood passes through these tiny filters. Normal results range from 90 – 120 mL/min,whilelevels below 60 mL/min for three or more months are a sign of chronic kidney disease (CKD).
  • Renal ultrasound scan: Produces an image of the kidneys. It can show obstructions, stones and tumors or cysts.
  • Kidney biopsy: Involves removal of a tiny piece of kidney tissue for examination under a microscope.

How is proteinuria treated?

Since proteinuria is a symptom and not a disease itself, medical care focuses on treating the underlying condition, such as normalizing blood pressure in people with hypertension or controlling blood sugar levels in those with diabetes.

People with nephrotic syndrome and fluid overload should restrict salt in their diet. The nephrologist may also recommend a mild restriction in protein intake.

ACE inhibitors are medications used primarily for the treatment of hypertension, but they are also very effective in reducing proteinuria regardless of whether the patient has hypertension or not.

Summary

Because proteinuria may or may not be related to a serious underlying disease, it is important to determine its cause and provide appropriate treatments as necessary to preserve kidney health and overall well-being.

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