Proteinuria is leakage of protein from the blood into the urine. This page explains what protein is, how it gets into the urine and what doctors can do to deal with any problems caused by proteinuria.
Protein is one of the three main types of chemical that make up our body (the others are fats and sugars). Protein is an important part of diet, and is contained in most types of food. Proteins have many functions, for example antibodies which are formed to protect against infection are proteins as are factors which help to manage clotting in our blood stream. Therefore protein is an important part of the plasma (watery part) of the blood, and the body does not want to lose protein. With a healthy kidney, when the body eliminates waste, protein is kept in the blood stream.
This is because protein in the blood is too large to pass through the tiny holes in the kidney filters. However, the filter can be damaged in kidney disease, so that protein can pass into the urine. The filter in the kidney is called a glomerulus, and many of the kidney diseases that cause nephrotic syndrome are called glomerulonephritis.
Normally there are no symptoms, but protein is detected by a routine urine test. The simple test with a dipstick (small plastic strip with a indicator paper attached) can detect very small amounts of protein, so that a positive test may not mean there is a serious problem with the kidneys.
If the amount of protein in the urine is very high, a condition called nephrotic syndrome may develop. Nephrotic syndrome causes water to build up in the body. The extra water can cause ankle swelling, or swelling in the hand (rings go tight on fingers) or around the eyes. Severe swelling can develop all the way up the legs and around the back. There may be swelling of the tummy or breathlessness due to water around the lungs. Click here for more detail on nephrotic syndrome.
Protein in the urine can be a marker of almost any type of kidney disease, so tests are always needed if the cause of proteinuria is to be confirmed. These are the most common (click on a disease for more information):-
- High blood pressure
- Reflux nephropathy
- Minimal change nephritis
Further tests may be necessary after protein has been detected by a simple ‘dipstick’ test on a small urine sample. This dipstick test is very sensitive, but cannot measure exactly how much protein is in the urine. To get an exact measurement, some urine needs to go to the laboratory. This can be done with a single small urine specimen, in which the laboratory measures the levels of protein and creatinine (‘protein-creatinine ratio’ or PCR for short). It is becoming more usual to measure the amount of protein in the urine by testing for albumin, and the result is an albumin-creatinine ratio (ACR). Albumin is a large part of the protein in the body, and anyone with a raised PCR will have a raised ACR, though the level will be slightly lower.
An ACR of less than 3 mg/mmol does not require further action.
An ACR of 3-30 does not usually require action, though would be checked annually.
An ACR of greater than 30 suggests significant leakage of protein through the kidneys, and the higher the level the more concern, especially if it is over 100.
If the ACR is high. the doctor will also take a full history, and check there is no-one else in the family with kidney disease. Several blood tests will be done, and your blood pressure will be measured. The size and shape of the kidneys may be measured in the X-ray department with an ultrasound (sound wave) scan.
Sometimes, to make a firm diagnosis of the cause of proteinuria, it is necessary to perform a kidney biopsy. This is the removal of a small fragment of kidney using a needle, so that the kidney can be examined under a microscope. Click here for more information on kidney biopsy
Many people with proteinuria turn out to have minor kidney disease with no problems in the long term, but some kidney disease can progress to kidney failure. Complications depend on the exact cause of proteinuria in each case, so read the information on the condition you have.
There are some problems which are common in all types of kidney disease with protein in the urine:-
- High blood pressure - Kidney disease commonly causes high blood pressure. This increases the risk of further kidney disease, and also the risk of heart attack and stroke. Drugs may be needed to control the blood pressure
- High cholesterol - In nephrotic syndrome (very high protein levels in the urine, click here for more details), high levels of cholesterol (a type of fat) may be found in the blood. If the cholesterol level is high over a period of years there is an increased risk of a heart attack. If the nephrotic syndrome is cured quickly, the cholesterol level will go down on its own. However, in some cases where a rapid cure is not possible, drugs to reduce the cholesterol may be needed.
The underlying kidney disease may be treatable with drugs. The type of treatment depends on the cause. Information is contained in the sections on each individual disease (see above for the types of kidney diseases).
Water retention can be treated by reducing the amount of salt and water taken in your diet each day. Some cases also require drugs to make the kidneys produce more urine.
High blood pressure can be treated by reducing salt in your diet, and often with drugs to take each day. A high cholesterol level may be treated with dietary control (eating less fat) and, in some cases, with cholesterol lowering drugs.
The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.