How does protein get into urine?
What is proteinuria?
Proteinuria is increased levels of protein in the urine. This condition can be a sign of kidney damage.
Proteins – which help build muscle and bone, regulate the amount of fluid in blood, combat infection and repair tissue – should remain in the blood. If proteins enter the urine they ultimately leave the body, which isn’t healthy.
Protein gets into the urine if the kidneys aren’t working properly. Normally, glomeruli, which are tiny loops of capillaries (blood vessels) in the kidneys, filter waste products and excess water from the blood.
Glomeruli pass these substances, but not larger proteins and blood cells, into the urine. If smaller proteins sneak through the glomeruli, tubules (long, thin, hollow tubes in the kidneys) recapture those proteins and keep them in the body.
However, if the glomeruli or tubules are damaged, if there is a problem with the reabsorption process of the proteins, or if there is an excessive protein load, the proteins will flow into the urine.
Normal amount of protein in the urine are less than 150mg/day. High levels of protein in the urine are associated with rapid decline in kidney function. It affects about 6.7 percent of the United States population. It is seen more in elderly and people with other chronic illnesses.
Symptoms of Proteinuria:
Often, someone with proteinuria doesn’t experience symptoms, especially if kidneys are just beginning to have problems. However, if proteinuria is advanced, symptoms can include:
- More frequent urination
- Shortness of breath
- Nausea and vomiting
- Swelling in the face, belly, feet or ankles
- Lack of appetite
- Muscle cramping at night
- Puffiness around the eyes, especially in the morning
- Foamy or bubbly urine
Proteinuria is diagnosed through a urine test. The patient provides a urine sample, which is examined in a lab. Doctors use a “dipstick” – a thin plastic stick with chemicals on the tip – to test part of the sample right away. If too much of any substance is in the urine, the chemical tip changes color.
The remainder of the urine is then examined under a microscope. Doctors look for substances that don’t belong in urine. These substances include red and white blood cells, bacteria and crystals that can grow and develop into kidney stones.
Treatment depends on the underlying condition that caused proteinuria. Each condition requires different treatments.
If kidney disease is confirmed, a treatment plan might include medication, diet changes, weight loss and exercise. Diabetes and hypertension patients with proteinuria might need blood pressure medication, and those with diabetes will have to control their blood sugar. Diabetes patients should receive glomerular filtration rate (GFR) blood tests every year and may be referred to a nephrologist, a doctor who specializes in the kidneys.
Pregnant women with preeclampsia should be watched carefully. The condition, although serious during pregnancy, usually resolves itself once the baby is born. Proteinuria patients with low blood pressure should schedule annual urine tests and blood pressure checks.
If proteinuria isn’t accompanied by diabetes, high blood pressure or any other medical condition, blood pressure medication still might be prescribed to prevent kidney damage. Blood pressure and urine should be checked every six months to make sure kidney disease isn’t present. As for those with mild or temporary proteinuria, treatment may not be necessary.
Can proteinuria be prevented?
Proteinuria cannot be prevented, but it can be controlled. Many of the causes of proteinuria can be treated (diabetes, high blood pressure, preeclampsia and kidney disease), allowing your healthcare provider to improve the condition.
What happens when chronic kidney disease or another serious condition is diagnosed or suspected?
A doctor who suspects kidney disease would repeat the urine test three times over three months. If the samples test positive for proteins each time, the patient likely has kidney disease. The earlier the diagnosis, the more chance doctors have to slow the disease and stop it from progressing.
Additional tests might include:
- Blood test to measure the levels of creatinine (chemical waste products). Healthy kidneys move these substances from the blood to the urine. If the kidneys are not working properly, creatinine will remain in the blood.
- Blood test to estimate the glomerular filtration rate (GFR). The GFR compares a patient’s size, age, sex and race to levels of creatinine and albumin in the blood. The GFR tells a doctor how well the kidneys are working and how far the kidney disease has advanced. It also helps the doctor plan treatment.
- Blood test to measure all proteins in the serum. The serum is part of the blood filled with proteins.
- Imaging tests like CT scans and ultrasounds. These tests show images of the kidneys, helping doctors spot problems like kidney stones, tumors or obstruction of the urinary tract.
- Urine protein electrophoresis. Doctors search for specific types of proteins in a urine sample. For example, the presence of a protein called Bence-Jones might indicate multiple myeloma (cancer of plasma cells).
- Immunofixation blood test. This test finds proteins called immunoglobulins – which are antibodies that fight infection – in the blood. Too many of the same immunoglobulins can indicate blood cancer.
- A kidney biopsy. This is a procedure involving removal of a tiny piece of kidney. Doctors examine the sample under a microscope to determine what caused the kidney disease and the extent of damage.
Journal of Nephrology and Urology is an Open Access peer-reviewed publication that discusses current research and advancements in diagnosis and management of kidney disorders as well as related epidemiology, pathophysiology and molecular genetics.
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Journal of Nephrology and Urology