Protein in urine (proteinuria): causes, tests and what happens next

Protein is present in the blood and is an important building block for the body. Kidney Research UK explains that healthy kidneys should only filter tiny amounts into the urine, because most protein molecules are too large to pass through the filters. Several proteins can be found in urine, but the most relevant to kidney disease is albumin. When albumin is the main protein lost, Patient.info says the term albuminuria is used.

A small amount of protein in urine is normal, as Patient.info points out, but larger amounts can be a sign of kidney problems or other illnesses. Even small degrees of albuminuria or proteinuria are associated with an increased risk of heart and blood vessel disease, according to Patient.info, which is why it is taken seriously when persistent.

The causes range from the harmless and temporary to serious kidney disease. Kidney Research UK lists diseases of the glomeruli, the kidney's filtering units, such as glomerulonephritis or diabetes, and says urine infection can cause proteinuria but usually with other signs of infection. It also lists heart failure and a first warning of eclampsia in pregnancy as conditions in which it may occur.

• Kidney damage from diabetes or high blood pressure, which Patient.info lists first among causes of kidney damage.

• Medicines harmful to the kidney, such as non-steroidal anti-inflammatory drugs, according to Patient.info.

• Systemic lupus erythematosus and other inflammatory conditions, and glomerulonephritis.

• Excess protein in the blood from conditions such as multiple myeloma, where free light chains spill into the urine.

• Urinary tract infection, in which proteinuria should disappear once the infection is treated.

• Standing for long periods, called orthostatic proteinuria, which Patient.info says is harmless and does not indicate kidney problems.

• Intense exercise, fever and dehydration, which can cause temporary proteinuria.

Patient.info says that proteinuria, like many other signs of kidney problems, often has no or few symptoms, particularly in the early stages, and that laboratory testing is the only reliable way to detect it. Foamy urine can be a symptom, but occasionally foamy urine is very common and can happen with cleaning chemicals in the toilet bowl or when a full bladder makes urine come out quickly. If urine is often foamy or becoming more so over time, speak to a doctor.

When very large amounts of protein are lost, as in nephrotic syndrome, fluid can leak out of the blood and cause swelling in the hands, feet, abdomen or face, according to Patient.info. Swelling, a marked reduction in urine, blood in the urine, severe back pain or feeling very unwell with proteinuria should be assessed promptly, so contact your GP or NHS 111.

Patient.info describes two main ways to test for proteinuria: a urine dipstick, which gives a result within minutes, and sending a sample to a laboratory for an accurate measurement. Dipsticks are less sensitive for proteinuria and will usually miss small amounts of protein in the urine, whereas laboratory analysis is more sensitive and measures the amount accurately. Ideally samples should be taken first thing in the morning, because orthostatic proteinuria is then excluded.

Kidney Research UK describes the urine albumin creatinine ratio (UACR) test as a test for looking into kidney health that measures the amount of protein in the urine, an early sign of kidney damage. It says the test is vital for those at risk of heart disease, diabetes, raised blood pressure and those with a family history of kidney disease. If a first test is abnormal, a GP will usually repeat it, and may check kidney function with a blood test and your blood pressure.

Kidney Research UK lists some warning signals that make it more likely to be an important kidney problem: large amounts of protein in the urine, positive tests for blood in the urine, abnormal kidney blood tests (creatinine or eGFR), high blood pressure and being young. If none of these are present, it says it is often best to keep an eye on the kidney tests, urine tests and blood pressure occasionally to make sure nothing develops, which can usually be done at the GP surgery.

Patient.info says that in the UK the National Institute for Health and Care Excellence (NICE) recommends a urine test for proteinuria in people with reduced kidney function on a blood test, diabetes, high blood pressure, a history of kidney disease such as glomerulonephritis, conditions that could damage the kidneys by blocking urine outflow such as an enlarged prostate or recurrent kidney stones, cardiovascular disease, complex diseases that may involve the kidneys such as lupus or myeloma, a family history of kidney failure or inherited kidney disease, and blood in the urine.

People at increased risk should have this test at least annually or as part of routine check-ups, with the exact frequency depending on the level of risk, and Patient.info says people with chronic kidney disease and diabetes should have a test at least once a year as part of regular reviews.

Patient.info says treatment of proteinuria depends on the cause, that doctors should determine the cause, and that if it is not clear or there is a lot of proteinuria they may refer to a kidney specialist (nephrologist). Treatment might include ACE inhibitors or angiotensin receptor blockers, which it describes as very good at treating kidney problems from diabetes, lifestyle changes such as losing excess weight, exercising and stopping smoking, and sometimes dietary changes. Keeping diabetes and high blood pressure under good control is important because both can harm the kidneys if not controlled.

Whether it can be cured depends entirely on the cause. Patient.info says proteinuria due to a urinary tract infection should go away completely once the infection has cleared, as should proteinuria due to a fever or exercise, while proteinuria due to kidney problems may be difficult to cure and treatment is usually aimed at slowing or stopping further kidney damage. Proteinuria, particularly in diabetes, can be a very early sign of kidney problems, so doctors check for it because early treatment to protect the kidneys is more likely to be successful.

If a test shows protein, do not assume the worst, but do not ignore it either. Make sure the test is repeated if advised, ask what your kidney function and blood pressure are, and ask when you should be re-checked. Kidney Research UK says not to hesitate to speak to your GP if you have any concerns about proteinuria. If you take anti-inflammatory painkillers regularly, ask a pharmacist or GP whether they are suitable for you, because Patient.info lists them among medicines harmful to the kidney.

On the NHS the first tests are done at the GP surgery, and a UACR is part of routine checks for people with diabetes or kidney disease. If the cause is unclear or there is a lot of protein, referral to a nephrologist follows. Private health checks and home tests are available, but a positive result still needs interpreting in context, with a repeat test and blood pressure and kidney function, so it is sensible to share any result with your GP.