Proteinuri

Normal protein secretion in the urine is less than 100 mg/day. In a healthy patient, most of the secreted protein originate from tubular mechanisms of secretion (Tamm-Horsfalls protein). Albumin is the dominating protein that filters in glomeruli and is therefore the best marker for pathological protein secretion due to either increased filtration in glomerular diseases or reduced tubular reabsorption in tubulointerstitial diseases. Therefore, we use albuminuria measured as albumin to creatinine ratio (ACR) as a measurement of the degree of proteinuria. When proteinuria is elevated, the tubular mechanisms of secretion contribute little to the proteinuria, and the protein to creatinine ratio (PCR) can be used as a measure of proteinuria.

 

Definition

 

ACR

Albumin per day

PCR

Proteinuria per day

Normal

0-3

0-30 mg/day

 

<200 mg/day

Microalbuminuria

3-30

30-300 mg/day

 

 

Proteinuria

30-300

300-3000 mg/day

50-300

500 mg-3 g/day

Nephrotic proteinuria

>300

>3 g/day

>300

>3 g/day

All kidney diseases present with degrees of proteinuria. If the proteinuria is in the nephrotic area (3 g/day) one can with certainty say the filtration barrier is damaged and there is a glomerular disease. If the nephrotic proteinuria occurs together with low S-albumin (30 g/L) and edema, the condition is named nephrotic syndrome and is a clear indication for kidney biopsy. If the patient present with a kidney disease where the proteinuria dominates the clinical picture, the kidney disease is said to present as nephrotic even though the the patient does not meet the other criteria for a nephrotic syndrome. the different glomerulonephritises have a tendency to present clinically with either a nephrotic or nephritic picture, which contributes to supporting a diagnosis before the results of the biopsy. Proteinuria is an important diagnostic tool to identify patients with kidney disease. In addition, the degree of proteinuria is an important marker for the prognosis of the kidney disease. Regular monitoring of proteinuria is therefore essential in kidney disease cases.