Generality
The presence of protein in the urine, also known as proteinuria, is a medical condition that occurs when there is an increased renal protein excretion.
In other circumstances, high proteinuria requires further investigation to determine whether, at the basis of this finding, there is a more severe health problem, such as kidney damage.
Increased protein in urine may also depend on various other conditions, such as: anemia, heavy metal poisoning, cystitis, diabetes, gout and pregnancy.
What's this
The significant presence of proteins in the urine, which doctors usually refer to as technical proteinuria, may be due to kidney damage or other rather serious conditions. Fortunately, urinary protein concentrations higher than normal can also be part of the physiological, as happens in particular situations, such as intense physical activity, fever and severe emotional stress.
A lot of proteins circulate in the blood of each individual, which are essential to the body to say the least; in fact, they perform transport functions (nutrients, gases, hormones, etc.), immune functions (defense against viruses, bacteria, etc.) and regulators (metabolism, coagulation, pH and blood volume, etc.).
At the kidney level, blood is purified from waste products and excess substances, undergoing a sort of sieving; the meshes of this very fine sieve are crossed by numerous substances, which end up in the filtrate to then be reabsorbed or expelled through the urine, according to biological needs. Among all these substances proteins are not included, which except for those of smaller dimensions, are almost absent in the filtrate and urine.
In the course of life it can happen that - due to pathologies or other problems (hypertension, diabetes, kidney infections, congenital malformations, etc.) - the meshes of the renal sieve become loose, allowing more protein to pass. Consequently, the protein concentrations of urine - assessed by a common test on a urinary sample - increase significantly.
Based on the recorded value, by analyzing the urine collected over a 24-hour period, the doctors talk about:
- Microalbuminuria (30-150 mg) *
- Mild proteinuria (150-500 mg) *
- Moderate proteinuria (500-1000 mg)
- Severe proteinuria (1000-3000 mg)
- Proteinuria in the range of nephrotic syndrome (> 3500 mg)
* Proteinuria is defined as urinary protein excretion greater than 150 mg per day; other sources raise this threshold to 300 mg, such that under 300 mg / day we speak of microalbuminuria and above 300 mg / day we speak of proteinuria .
Why do you measure
Proteinuria may indicate the presence of damage to the kidneys: in general, these organs do not allow the body to pass molecules, such as proteins, into the urine. However, in the presence of certain diseases or particular conditions, these substances escape renal filtering and are excreted.
For this reason, it is appropriate to investigate the causes of the presence of too high proteinuria, especially if this is continuous.
To remember
The proteinuria manifests itself before the function of purification of the blood from the kidneys is compromised; as a result, the presence of protein in the urine is an early sign of kidney disease.
For this reason, the detection of proteinuria should never be neglected, on pain of ignoring a potentially progressive nephropathy towards renal failure.
When prescribed
Proteinuria is a parameter that is evaluated with the urine test . This is prescribed as part of routine analyzes or as a follow-up to a previous positive urinary protein test.
This feedback is useful to the doctor for:
- Reveal an excessive elimination of proteins in the urine;
- Support in assessing and monitoring renal function;
- Understanding whether kidney damage is present.
In individuals in whom nephropathy is already known (eg primary glomerulonephritis or diabetic nephropathy), the presence of proteinuria is a predictor of the risk of evolution towards more advanced degrees of renal failure.
Urine test and urinary dipstick
A semi-quantitative test called a urinary dipstick (from the English dip-and-read test strip, therefore based on the use of reactive strips) is used as a screening test for the general population; if the result is positive, the test can be repeated a few days later to exclude occasional increases associated with non pathological conditions. When the diagnosis is confirmed, or severe urinary tract is appreciated, urine is collected within 24 hours; it is also possible to evaluate the proportions and concentrations of the various plasma proteins by urinary electrophoresis (particularly important when it is suspected that proteinuria is linked to an increased synthesis of plasma proteins, as occurs in multiple myeloma).
Reading the stick gives essentially qualitative information, which can be divided as follows:
- "negative";
- "traces" (corresponding approximately to 10-20 mg / dL);
- "protein 1+" (about 30 mg / dL);
- "protein 2+" (about 100 mg / dL);
- "3+ proteins" (about 300 mg / dL);
- "4+ proteins" (about 1000 mg / dL).
Instead of the dipstick or the traditional urine test within 24 hours, doctors are increasingly using a new technique based on the ratio between the urinary concentrations of albumin (the most abundant plasma protein) and creatinine (a waste product). resulting from normal muscle metabolism). This test - also known as ACR, from the English albumin-to-creatinine ratio - considers any situation where there is more than 30 mg of albumin per gram of creatinine (30 mg / g or 30 mcg / mg) worthy of diagnostic investigations . Also in this case, in the face of positive values, the examination is repeated after one or two weeks and - if the subject is positive again - is followed by other in-depth examinations to assess renal function.
Normal values
Within certain limits, a minimal presence of protein in the urine can be considered normal. In the same way, the high levels found in particular conditions, such as after an intense physical effort or after an illness, can be considered not worrying.
When we talk about protein in the urine the following values are normal:
- Occasional urine sample: between 0 and 20 mg / dl;
- 24-hour urine collection: less than 150-200 mg / dl.
High Urine Proteins - Causes
As anticipated, hypertension and diabetes are the two main risk factors for proteinuria, whose incidence increases significantly with increasing age and BMI.
The presence of proteins in the urine can also be associated with various other conditions and diseases, including:
- Acute glomerulonephritis;
- Focal glomerulonephritis;
- Amyloidosis;
- IgA nephropathies dependent;
- Heart diseases (pericarditis, heart failure);
- Multiple myeloma;
- Leukemia;
- Malaria;
- Sickle cell anemia;
- Rheumatoid arthritis;
- Sarcoidosis;
- Systemic lupus erythematosus;
- Heavy metal poisoning;
- Mesangial proliferation glomerulonephritis;
- Renal infection;
- Bladder cancer;
- Potentially kidney toxic drugs;
- Goodpasture syndrome;
- Polycystic kidney disease;
- Urinary tract infection.
In addition to these purely pathological circumstances, sensitive increases in urinary protein concentrations can also be associated with physiological conditions (in this case we speak of transient proteinuria ). Exposure to cold or intense heat, fever, severe emotional stress and strenuous exercise (both sports and work), can significantly increase the amount of protein found in the urinary sample. Pregnancy can also be associated with mild proteinuria, although significant protein concentrations should lead to suspicion of an ongoing urinary infection or the development of pre-eclampsia.
Orthostatic proteinuria is a relatively common pathology in children and young adults, which is associated with significant protein losses in the urine during the standing (orthostatic) position. Presumably, this condition is linked to the increase in pressure on the renal glomeruli, which also forces the passage of proteins between the meshes of these filters. In the lying (clinostatic) position, the pressure decreases and the loss of protein is reduced; doctors consider this disorder of benign origin, given that in the great majority of cases it spontaneously regresses with growth. Orthostatic proteinuria is diagnosed through a urine collection divided into 2 samples: one obtained in an upright position and one obtained at night, after the young patient has rested for a few hours and has emptied the bladder before going to bed.
Protein in urine: symptoms and treatment
Among the symptoms of proteinuria - generally absent in mild or moderate cases - include the presence of foam in the urine and edema, that is the abnormal accumulation of fluids in the interstitial spaces, due to a decrease in plasma oncotic pressure. Water retention, with the appearance of edema and swelling (especially in the hands, feet and ankles, and therefore in the face and abdomen in the most serious cases), is however a late sign, typical of the more severe stages of proteinuria.
The treatment of proteinuria is aimed at eliminating, or at least controlling. the causes that led to the increase in protein concentration in urine; hypertension, for example, can be controlled by ACE inhibitor drugs or angiotensin receptor antagonists (ARBs).
Low Urine Proteins - Causes
The complete absence or low values of proteins in the urine are not associated with any particular type of pathology. For this reason, low levels of this parameter should not cause any concern.
Some antihypertensive drugs - belonging to the class of ACE inhibitors (ramipril, lisinopril, enalapril etc.) and of angiotensin II receptor antagonists (eg losartan, valsartan, irbesartan) - can reduce proteinuria and slow the progression of the associated nephropathy towards more severe degrees of chronic renal failure.
How to measure it
The determination of proteinuria is carried out on a sample of urine in the morning or on urine collection within 24 hours.
Preparation
For the evaluation of proteins in urine, a sample must be collected in a special clean container.
Urine is not affected by food, so there are no contraindications to the fact that the sample is taken fasting or after eating.
Situations that can distort proteinuria
Some non-pathological situations can provide altered results of protein dosing in urine:
- Blood contamination (eg menstruation);
- Urinary tract infections;
- Intense physical exercise;
- Prolonged upright station (orthostatic proteinuria).
As a result, urine tests designed to control proteinuria should be performed without these conditions.
Interpretation of Results
The kidney has the task of keeping proteins in the body, so these should not be eliminated in the urine.
On the contrary, if the analyzes indicate their presence and if the fact is isolated, this could depend on urinary tract infections, drugs, intense exercise or stress, emotional or physical.
In some people, proteins are present in the urine during the day and absent at night, when the individual is lying down (orthostatic proteinuria).
If the presence of proteins in the urine is constant, however, it could be a renal disease such as, for example, acute and / or chronic glomerulonephritis. Protein in the urine is, in fact, an alarm bell and can indicate damage to the kidneys. When organ impairment is established, protein concentration is generally associated with the severity of the damage; the increase in proteinuria over time indicates a worsening of the condition and a decrease in renal function.
In pregnant women, high concentrations of protein in the urine may be associated with pre-eclampsia. For this reason, it is very important to periodically check this parameter during gestation.
