Abstract: SA-PO0927
Limitations of Spot Albuminuria and Total Proteinuria Measures for Indirect Nonalbumin Proteinuria Quantitation
Session Information
- Pathology: Updates and Insights
November 08, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Pathology and Lab Medicine
- 1800 Pathology and Lab Medicine
Author
- Robey, Robert Brooks, Southeast Louisiana Veterans Health Care System, New Orleans, Louisiana, United States
Introduction
Spot urinary albumin and total protein measures normalized for urinary creatinine excretion are routinely used to quantitate albuminuria and total proteinuria, respectively. It is also common practice to use the quantitative difference between these measures to estimate the amount of non-albumin protein (NAP) in urine, particularly in renal tubular dysfunction.
Case Description
New onset 1+ proteinuria was noted on routine urinalysis in a patient with nonoliguric acute kidney injury. Contemporaneous spot urinary albumin:creatinine (UACR) and total protein:creatinine (UPCR) ratios revealed stage A2 range albuminuria (79 mg/g) and non-nephrotic range proteinuria (1200 mg/g). Direct quantitative comparison of these measures also suggested >93% urinary NAP content (1200 mg/g – 79 mg/g = 1121 mg/g). Protein electrophoresis of both serum (SPEP) and urine (UPEP) was also performed in parallel to directly assess protein composition and address the presence of both hypoalbuminemia (2.5 g/dL) and an apparent increase in the associated total serum globulin fraction (total protein 7.0 g/dL – 2.5 g/dL = 4.5 g/dL). Notably, albumin was found to comprise 97% of the total urinary protein on UPEP (see Table), suggesting that the true NAP content was quantitatively trivial.
Discussion
The spot UACR is widely employed to quantitate albuminuria and is a standard metric for chronic kidney disease risk stratification and management. While the clinical utility of the UPCR is also well established, direct quantitative comparisons are confounded by a variety of factors that include protein heterogeneity, lack of standardization, a nonlinear relationship with the UACR, and differential interference by associated clinical covariates. The marked discrepancy between electrophoretic and spot urine NAP estimates in this case (<3% vs >93%) illustrate the potential limitations of inferring urinary NAP content from spot UACR and UPCR measures and suggest a need for independent laboratory validation.
Protein Electrophoresis Results
| SPEP | UPEP | |||
| [Serum Protein] (g/dL) | % Total | [Urine Protein] (mg/dL) | % Total | |
| Total Protein | 6.2 | 100 | 47.9 | 100 |
| Albumin | 2.1 | 34 | 46.3 | 97 |
| α1-Globulin | 0.3 | 5 | 0.0 | 0 |
| α2-Globulin | 0.7 | 12 | 0.0 | 0 |
| β-Globulin | 1.0 | 17 | 0.0 | 0 |
| γ-Globulin | 2.0* | 33 | 0.0* | 0 |
*No M spike