Urine Levels Of Proteins
Proteinuria
Proteinuria means the presence of an excess of serum proteins in the urine. The excess protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine (bilirubinuria), or drugs such as pyridium. Up to 150 mg a day of protein may be excreted by a normal person. Proteinuria can also be caused by certain biological agents, such as Avastin used in cancer treatment, or by excessive fluid intake (drinking in excess
of 4 litres of water per day).
Causes
There are three main mechanisms to cause proteinuria:
1. Due to disease in glomerulus
2. Because of increased quantity of proteins in serum (overflow proteinuria)
3. Due to low reabsorption at proximal tubule (Fanconi syndrome)
Measurement
Conventionally, proteinuria is diagnosed by a simple dipstick test, although it is possible for the test to give a false negative reading, if the protein in the urine is composed mainly of globulins or Bence-Jones proteins. Alternatively the concentration of protein in the urine may be compared to the creatinine level in a spot urine sample. This is termed the protein/creatinine ratio (PCR). Proteinuria is defined as a protein/creatinine ratio greater than 45 mg/mmol (which is equivalent to albumin/creatinine ratio of greater than 30 mg/mmol or approximately 300 mg/g) with very high levels of proteinuria being for a PCR greater than
100 mg/mmol.
