Proteinuria may represent an early manifestation of a serious kidney disease in asymptomatic patients, but it may also be a temporary or nonprogressive kidney abnormality. For adults, proteinuria refers to the amount of protein in urine that exceeds 150 mg per day. For children, the amount of protein in urine is age and weight related. Generally, Proteinuria in infants (under one year of age) and children (over one year to ten years old) is defined as urine protein excretion greater than 110mg/m2 and 85mg/m2 per day, and newborns (up to 30 days) greater than 145 mg/ m2 is a proteinuria. Proteinuria occurs temporarily or continuously, with severe and persistent proteinuria reacting to the clinical risk of worsening renal function. Many of the mild proteinuria found in medical examinations do not cause deterioration of kidney function, which is called Benign Proteinuria. About 20% of the composition of normal urine protein is low-molecular weight protein, such as certain immunoglobulins, 40% albumin, and 40% uromodulin, also known as Tamm-Horsfall protein.

There are four main possible causes of excessive urine protein excretion:

Renal filament permeability changes normal plasma proteins to be filtered out (e.g. nephrotic syndrome).
The tubules cannot reabsorb a small amount of protein that is normally filtered out (e.g. Fanconi syndrome).
Renal filtration of a large amount of abnormal plasma proteins exceeds the limit of tubular back absorption (e.g. light chain of immunoglobulin secreted by multiple myeloma).
Increase the secretion of tissue proteins in the presence of inflammation or tumors (e.g., when pyelonephritis, Tamm-Horsfall mucin secretion).

Classification of Proteinuria

There are many ways to classify proteinuria. The simple and practical way to classify proteinuria is based on the amount of proteinuria, its persistence, and whether it is related to other diseases. In addition, some people are classified according to the source of urine protein.

Firstly, Proteinuria, which means proteinuria with no other kidney disease, systemic disease or urine sludge. This proteinuria can be distinguished from Benign Simple Proteinuria and Persistent Simple Proteinuria, which may be due to functionality such as fever, strenuous exercise, cold, emotional stress, and pregnancy. Others are posture related, where 80% of these patients present with transient proteinuria, while the rest 20% of persistent proteinuria may have a deterioration in renal function. However, there are many benign simplex proteinuria for unknown reasons. Patients with persistent simplex proteinuria may have different prognosis due to many possible reasons, and some patients may have a worsening of renal function.

Secondly, disease-related proteinuria, which can easily differentiate the origin of urine protein according to the amount of urine protein; those with less than 2 grams of urine protein per day are usually tubular and interstitial lesions, vascular kidney Lesions, partial filigonous lesions and some systemic diseases such as hypertension, while proteinuria with greater than 3.5 grams per day is mostly a kidney disease, which can be caused by systemic diseases or kidney disease itself.

Common causes of proteinuria

Emotional stress
Heat Stroke
Vigorous sports
Partial Acute Diseases
Postural proteinuria

Determination of proteinuria

Test paper analysis is the most common method used in outpatient settings to determine the amount of urine protein.
Yellow in the presence of anuria proteins signifies that the proteins in the urine interferes with the binding of the dye to the buffer, turning yellow to green. Pseudo-positive results may occur in some cases, such as urine is too alkaline (PH value greater than 7.5), long dipping of the test paper, very high urine concentration, large hematuria, certain drug effects (such as penicillin and sulfonamides), pyuria, and semen or vaginal secretions.

In contrast, pseudo-negative urine may occur when urine is diluted (specific gravity less than 1.015) and this urine protein is non-albumin or molecular weight is low. This method is more sensitive to albumin and less to globulin and light chain proteins.

The SSA (Salfosalicylic acid) turbidity test also provides a qualitative screening of urine proteins, which is sensitive to the test paper on light chain proteins, up to 4mg/dl, pseudo-positive from pseudo-benicillin or sulfonamide drugs taken within three days, as well as from injections of radioseners. Most of the reason for pseudo-negative is that the urine is too thin. Both methods are semi-quantitative or qualitative measurements. Most patients with persistent proteinuria should determine the loss of urine protein for 24 hours. The amount of creatinine should also be measured to determine urine. Whether it is collected completely, the average adult males discharge is about 16 to 26 mg per kilogram of creatinine per day and 12 to 24 mg for females. Daily creatinine discharge may be reduced in older and malnourished patients.

Definitions of normal values may vary depending on products and hospitals. Consult your doctor if you have any concerns.

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