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Comparison of Spot Urine Protein Creatinine Ratio with 24-Hour Urine Protein for Estimation of Proteinuria
Patil P, Shah V, Shah B | Journal of the Association of Physicians of India | May 2014, Vol. 62
Department of Pathology, TN Medical College & BYL Nair Hospital, Mumbai
Slide 1 — Background & Rationale
- Urinary protein measurement is a key marker of renal impairment
- Early detection allows treatment before irreversible damage occurs
- Repeated proteinuria monitoring is needed in glomerulopathies, diabetes, hypertension, and nephrotic syndrome
The Problem with 24-Hour Urine Collection (Gold Standard):
- Cumbersome and error-prone (incomplete collection, bacterial growth, incorrect timing)
- Requires hospital admission
- Inconvenient for repeated follow-up
The Solution — Spot UP/C Ratio:
- Creatinine excretion is relatively fixed, so dividing urine protein by creatinine nullifies hydration variability
- Can be collected at any time; simple, outpatient-friendly
- Endorsed by the National Kidney Foundation (NKF K/DOQI guidelines)
Slide 2 — Study Design & Methods
| Parameter | Detail |
|---|---|
| Study type | Prospective |
| Setting | Tertiary care hospital, Mumbai |
| Period | November 2008 – May 2010 |
| Participants | 241 total (208 cases + 33 healthy controls) |
| Age range | 18–65 years |
Disease subgroups among cases:
- Hypertension (HT): 83
- Diabetes Mellitus (DM): 72
- DM + HT: 17
- Nephrotic Syndrome (NS): 18
- Pregnancy-Induced Hypertension (PIH): 16
Exclusions: Incomplete 24-hr collections (21), haematuria (11), pyuria (8), contaminated samples (15)
Laboratory Methods:
- 24-hr urine protein: Sulphosalicylic acid method
- Creatinine: Modified Jaffe's method (colorimetry)
- UP/C ratio = Urine protein (g/L) ÷ Urine creatinine (g/L)
- Statistics: Pearson's correlation, ROC analysis (MedCalc), regression analysis
Slide 3 — Key Results
Correlation between UP/C ratio and 24-hr urine protein:
- Overall r = 0.98, p < 0.05 — excellent correlation
- Significant across all disease subgroups (r = 0.96–0.99)
Mean values (Cases vs. Controls):
| Cases (n=208) | Controls (n=33) | p value | |
|---|---|---|---|
| 24-hr protein (g/24hr) | 0.821 ± 1.336 | 0.034 ± 0.036 | 0.001 |
| UP/C ratio | 0.716 ± 1.155 | 0.027 ± 0.027 | 0.001 |
Repeatability: No significant difference between first and repeat UP/C samples (p = 0.191) — confirms reproducibility
Regression formula:
24-hr protein (g/24hr) = [1.005 × UP/C ratio] + 0.078 (R² = 0.895)
Slide 4 — ROC Analysis: Cutoff Values
Detecting Macro-proteinuria (>150 mg/24hr)
| UP/C Cutoff | Sensitivity | Specificity | +LR | −LR |
|---|---|---|---|---|
| >0.1171 | 100% | 98.1% | 53.5 | 0 |
| >0.1481 | 96% | 99.1% | 102.8 | 0.04 |
| >0.1604 | 95% | 100% | >101.7 | 0.05 |
Detecting Nephrotic Range Proteinuria (>3.5 g/24hr)
| UP/C Cutoff | Sensitivity | Specificity | +LR | −LR |
|---|---|---|---|---|
| >2.5624 | 100% | 96.4% | 27.6 | 0 |
| >2.867 | 93.3% | 98.4% | 60.0 | 0.07 |
| >3.2318 | 80% | 100% | >154.4 | 0.2 |
Area under ROC curve = 0.9 for both thresholds (p < 0.05) — indicates a highly accurate test
Slide 5 — Clinical Interpretation of Cutoffs
For screening (rule out disease):
- Use UP/C >0.1171 → 100% sensitivity, misses no true positives
When clinical suspicion is low (rule in disease):
- Use UP/C >0.1604 → 100% specificity, no false positives
For nephrotic range screening:
- Use UP/C >2.5624 → 100% sensitivity
For confirming nephrotic proteinuria (low suspicion):
- Use UP/C >3.2318 → 100% specificity
Slide 6 — Discussion Highlights
- Results are consistent with similar studies (Chitalia et al., Antunes et al., Ginsberg et al.)
- UP/C ratio is particularly valuable for:
- Children and pregnant women (24-hr collection difficult)
- Diabetic and hypertensive patients requiring frequent follow-up
- Low-resource settings where albumin-creatinine ratio is too costly
- UP/C ratio can substitute albumin-creatinine ratio when ACR > 0.5 (per NKF K/DOQI guideline 5)
- Caveat: Factors affecting creatinine excretion (age, sex, muscle mass) should be considered when interpreting results
Slide 7 — Conclusions
✅ Spot UP/C ratio shows excellent correlation with 24-hr urine protein (r = 0.98)
✅ Reliable for detecting macro-proteinuria >150 mg/24hr and nephrotic range proteinuria >3.5 g/24hr
✅ Simple, reproducible, and convenient — no hospital admission needed
✅ Overcomes pitfalls of 24-hr urine collection
✅ Recommended for routine clinical practice for monitoring proteinuria
Published in JAPI, May 2014 | Area under ROC = 0.9 | n = 241 participants
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