What is it?
Proteinuria is a condition characterised by the presence of greater than normal amounts of protein in the urine. It is associated with a variety of different diseases and is sometimes seen in those who are apparently healthy. Mild or transient proteinuria may become more severe over time.
Plasma, the liquid portion of blood, contains many different proteins. One of the many functions of the kidneys is to conserve plasma protein so that it is not excreted along with waste products when urine is produced. There are two mechanisms that normally prevent protein from passing into urine: (1) the glomeruli provide a barrier that keeps most larger plasma proteins inside the blood vessels and (2) the small proteins that do get through are almost entirely reabsorbed by the tubules. For additional details on kidneys and how they function, see the page on How Kidneys Work on the DaVita website.
Proteinuria most often occurs when either the glomeruli or tubules in the kidney are damaged. Inflammation and/or scarring of the glomeruli can allow increasing amounts of protein and sometimes red blood cells (RBCs) to leak into the urine. Damage to the tubules can prevent protein from being reabsorbed. Proteinuria may also develop when too much of a small protein is present in the blood and the tubules cannot reabsorb all of it.
A variety of diseases and conditions are associated with proteinuria. Two of the most common causes are:
Others causes include:
- immune disorders (e.g., systemic lupus erythematosus (SLE), IgA nephropathy, Goodpasture’s syndrome)
- exposure to toxins
- kidney cancer
- multiple myeloma
Pregnant women are frequently screened for proteinuria because its development is associated with preeclampsia (also know as toxaemia), a hypertensive disorder that can cause oedema, nausea and headaches during pregnancy. Preeclampsia can be dangerous for both the mother and her baby.
Proteinuria due to the presence of excess small proteins in blood may be seen in multiple myeloma (free immunoglobulin light chains) and in conditions that cause the breakage of red blood cells (release of haemoglobin).
Healthy people can have transient or persistent proteinuria. It is associated with stress, exercise, fever, aspirin therapy, and exposure to cold. Some people excrete more protein into the urine when they are standing up than when they are lying down (orthostatic proteinuria).
Signs and symptoms
There are frequently no symptoms associated with proteinuria, especially in mild cases. Large amounts of protein may cause the urine to appear foamy. Significant loss of protein from the blood can affect the body’s ability to regulate fluids, which can lead to swelling in the hands, feet, abdomen and face. When symptoms are present, they are usually associated with the condition or disease causing proteinuria.