[Reference intervals of urinary biochemical analysis in Japanese men]

Area of Science:

• Nephrology
• Clinical Chemistry
• Biomarker Discovery

Background:

• Establishing accurate reference intervals for urinary biomarkers is crucial for diagnosing kidney disease.
• Age-related changes in renal function can impact urinary protein excretion.
• Previous studies have not comprehensively defined age-specific reference ranges for multiple urinary proteins in healthy men.

Purpose of the Study:

• To determine age-specific reference intervals for urinary albumin, immunoglobulin G (IgG), transferrin, alpha 1 microglobulin, and N-acetyl-beta-D-glucosaminidase (NAG) in healthy adult men.
• To investigate the influence of age on these urinary biomarkers, adjusting for urinary creatinine levels.

Main Methods:

• Urine samples were collected from 421 healthy men aged 30-59 years with normal blood pressure and glycemic control.
• Urinary concentrations of albumin, IgG, transferrin, alpha 1 microglobulin, NAG, and creatinine were measured.
• Reference intervals were calculated using the iterative truncation method after logarithmic transformation, stratified by age group (30s, 40s, 50s).

Main Results:

• Urinary creatinine levels significantly decreased with increasing age.
• Concentrations of albumin, IgG, transferrin, alpha 1 microglobulin, and NAG did not change significantly with age when expressed in absolute terms.
• However, when normalized to creatinine excretion (e.g., g/creatinine), the levels of these urinary components increased with age.

Conclusions:

• Age-adjusted reference intervals are necessary for accurate interpretation of urinary biomarker levels in men.
• The observed increase in urinary protein excretion per gram of creatinine with age suggests potential subtle age-related changes in kidney filtration or reabsorption.
• These findings provide valuable data for establishing normative values and improving the early detection of renal abnormalities.