Normal Urine Protein-to-Creatinine Ratio in Adults
A normal urine protein-to-creatinine ratio (PCR) in adults is less than 200 mg/g (or <0.2 mg/mg), with values ≥200 mg/g indicating abnormal proteinuria that warrants further evaluation. 1
Standard Reference Ranges
The KDIGO guidelines categorize PCR measurements into three clinically relevant ranges 1, 2:
- Normal to mildly increased (A1): PCR <150 mg/g (<15 mg/mmol)
- Moderately increased (A2): PCR 150-500 mg/g (15-50 mg/mmol)
- Severely increased (A3): PCR >500 mg/g (>50 mg/mmol)
However, the National Kidney Foundation establishes the practical clinical threshold at <200 mg/g as the normal range for total protein-to-creatinine ratio in the general adult population. 1, 3
Albumin vs. Total Protein Measurements
For albumin-specific measurements, different thresholds apply 1:
- Normal: ≤30 mg albumin/g creatinine
- Microalbuminuria: 31-300 mg albumin/g creatinine
- Macroalbuminuria: >300 mg albumin/g creatinine
The American Diabetes Association recommends albumin-to-creatinine ratio (ACR) for screening patients with diabetes or at high risk for chronic kidney disease, as it is more sensitive for detecting early kidney damage. 1
Clinical Context and Interpretation
At very high levels of proteinuria (PCR 500-1,000 mg/g or higher), measurement of total protein rather than albumin is acceptable and more practical. 1 This is because albumin assays may become less reliable at nephrotic-range proteinuria.
Research studies consistently support these thresholds. A landmark study found that healthy subjects never exceeded 100 mg/g, while nephrotic syndrome patients always exceeded 2,000 mg/g (equivalent to 3.5 g/day protein excretion). 4 Another study established that a ratio <0.2 mg/mg (equivalent to 200 mg/g) represents normal limits. 5
Important Collection Considerations
To ensure accurate results, patients should 1:
- Avoid vigorous exercise for 24 hours before specimen collection, as physical activity causes transient proteinuria elevation
- Provide first-morning void samples when possible (especially for children and adolescents to avoid orthostatic proteinuria)
- Avoid collection during menstruation or active urinary tract infection
Confirmation Requirements
A single elevated PCR should not be considered diagnostic. The National Kidney Foundation recommends confirming abnormal values with repeat testing, particularly in patients with diabetes mellitus where 2 of 3 positive samples over time are needed to establish persistent proteinuria. 1
Sex-Specific Considerations
Some evidence suggests sex-specific cutoffs may be more accurate (>17 mg/g for men and >25 mg/g for women), though the standard 30 mg/g cutoff for albumin remains more widely recommended in clinical practice. 1, 6
When 24-Hour Collection May Be Needed
While spot PCR has largely replaced 24-hour collections, timed collections remain useful in specific circumstances 1, 3:
- Extremes of body habitus (cachexia, muscle atrophy, extreme obesity) where creatinine excretion is abnormal
- Confirmation of nephrotic syndrome (>3,500 mg/day) for thromboprophylaxis decisions
- Patients with glomerular disease requiring immunosuppression initiation or intensification
The correlation between spot PCR and 24-hour protein excretion is excellent (r=0.97) across a wide range of proteinuria levels, validating the use of spot samples for routine clinical assessment. 4