Analysis of proteinuria: reference limits for urine excretion of albumin, protein HC, immunoglobulin G, k- and Δ-immunoreactivity, orosomucoid and α₁-antitrypsin

Abstract

Efficient use of assessment of urine protein excretion in nephrological practice requires adequate reference intervals. To determine the upper reference limits of urine albumin, protein HC (α₁-microglobulin), immunoglobulin G (IgG), orosomucoid (α₁-acid glycoprotein), α₁-antitrypsin, and k- and Δ-chain immunoreactivities, the concentrations of these proteins were measured in urine samples from 95 healthy, adult individuals, using rapid, generally available methods and with conditions for urine collection which secured stable protein levels. The obtained values were expressed inmgl⁻¹, as the urine protein-creatinine index and as fractional protein-creatinine clearance.

No differences were found between the upper reference limits in the first voided morning urine samples and the randomly collected urine samples, nor between the upper reference limits in urine samples collected from males and females. The urinary excretion of the tested proteins did not correlate to age, positive dipsticks for haematuria nor to granular casts in urine sediment. Thus, the same upper reference limits can be used for both sexes and regardless of the type of urine collection.

The upper reference limits of urine protein-creatinine index found in this study were: for albumin, 3.8 mg mmol⁻¹; for protein HC, 0.7 mg mmol; for IgG, 0.8mg mmol⁻¹; for orosomucoid, 0.7 mgmmol⁻¹; for α₁-antitrypsin, 0.2 mg mmol⁻¹, and for k-immunoreactivity 0.7 mg mmol⁻¹. The upper reference limit for Δ-immunoreactivity was below the detection limit.

Key Words:

• fractional protein creatinine clearance
• protein selectivity index
• proteinuria
• reference limits