What is proteinuria?
Proteinuria is the medical term for the presence of higher than normal levels of protein in the urine. There are different types of protein that may be present in the urine. This can be divided into albumin and non-albumin proteins. Albumin, a blood protein, is among the more abundant of the serum proteins and is important in determining if the presence of urinary protein is a problem or not. This should not be confused with hematuria which is the presence of whole red blood cells, fragments or casts in the urine, although hematuria and proteinuria may occur simultaneously.
How does proteinuria occur?
Most proteins in the blood are too large to be filtered out into the urine under normal circumstances. Small amounts of protein may enter the urine and are quickly reabsorbed. Some of these proteins remain in the urine and are passed out. In proteinuria, large amounts of protein are lost in the urine. This may occur if the kidneys are unable to reabsorb the proteins, the level of proteins in the blood is too great for maximum reabsorption functions to be effective or if there is damage to the glomerular apparatus and proteins leak into the urine.
In the course of a day, protein is excreted in the urine and this is a normal occurrence. It is usually less than 150mg per 24 hour period and albumin secretion may be less than 5mg per liter. However, levels of albumin in the urine that is between 30 and 300mg/day (microalbuminemia) may not be detected upon a urine dipstick test and will require radioimmunoassay techniques to be confirmed.
Symptoms of Proteinuria
Proteinuria is usually asymptomatic, meaning that a person will not notice any signs or symptoms due to the presence of high levels of protein in the urine. In severe proteinuria, frothy or foamy urine may be evident. Proteinuria is a sign of some underlying kidney or systemic disease – urinary symptoms are often related to these diseases and not due to the proteinuria itself. However, late symptoms of severe or prolonged proteinuria may be seen as swelling of the legs, hands, face and/or abdomen.
Proteinuria may occur in a healthy person with no kidney disease or systemic disorders. This is not a normal occurrence and is a sign that the body may be under strain. However it does not indicate any serious disease and often resolves on its own. Transient proteinuria may be detected after strenuous physical activity, during periods of stress, fever, using aspirin or cold conditions.
There are also some causes of persistent proteinuria that may not be related to kidney disease. In orthostatic proteinuria, a healthy person may pass out more urine when standing up than when lying down. This is usually less than 1 g/L and is not present in the morning urine (after awaking from sleep) although it will be detected throughout the day.
Types of Proteinuria
Proteinuria can be broadly divided into the following categories :
In most cases, transient proteinuria will resolve on its own and is not indicative of serious disorders. However, certain conditions like congestive heart failure may result in transient proteinuria, especially in the early stages.
Orthostatic proteinuria is a benign condition seen in a healthy young person. Changes in position may result in proteinuria.
Persistent proteinuria is a cause for concern as it is indicative of kidney disease or other systemic disorders that are impacting upon renal function.
Causes of High Protein in Urine
With the prevalence of diabetes and hypertension, these conditions have to be excluded if proteinuria is detected upon routine investigation. In most cases, proteinuria is asymptomatic. Foamy urine may be the only sign of proteinuria initially but in severe cases, there may be swelling of the face, limbs and abdomen.
- Chronic kidney disease
- Diabetes mellitus
- Heart failure
- Infection (localized – kidney, heart; systemic – malaria)
- Poisoning – heavy metals, arsenic, copper (Wilson’s disease)
- Renal artery stenosis
- Rheumatoid arthritis
- Systemic lupus erythematosus (SLE)
- Cold exposure
- Vigorous exercise
- Orthostatic (postural) proteinuria
- Abdominal surgery
- Congestive heart failure