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 the kidneys aren’t performing the job of 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 and maintaining 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.
Usually there are no obvious symptoms for the condition. If the protein loss is heavy, the urine has a frothy appearance, and would most likely have other symptoms, such as oedema, where there is an excess of water in the body tissues.
- Diseases of the glomeruli (the kidney’s filtering units), for example, glomerulonephritis or diabetes
- Urine infection can cause proteinuria, but usually there are other signs of this – see cystitis/urinary tract infections.
- Proteinuria can also be a symptom of some other conditions and diseases; for example: congestive heart failure or a first warning of eclampsia in pregnancy.
- Sometimes a positive dipstick for protein isn’t abnormal; for example, concentrated samples first thing in the morning or if you have become dehydrated. Lab tests can provide information on this (protein/creatinine ratio or albumin/creatinine ratio).
- Temporary proteinuria may occur after vigorous exercise or if you have a high fever.
- Sometimes, almost always in children, proteinuria can be detected later in the day, but not during the day. This is known as orthostatic proteinuria and is usually harmless.
- Because 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 the 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’re also very effective in reducing proteinuria, regardless of whether the patient has hypertension or not.