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Abstract: SA-PO137

The Urine Protein-Albumin Gap as a Predictor of Multiple Myeloma

Session Information

Category: Onconephrology

  • 1600 Onconephrology

Authors

  • Hundemer, Gregory L., Ottawa Hospital, Ottawa, Ontario, Canada
  • Imsirovic, Haris, Institute for Clinical Evaluative Sciences, Ottawa, Ontario, Canada
  • Akbari, Ayub, Ottawa Hospital, Ottawa, Ontario, Canada
  • Sood, Manish M., Ottawa Hospital, Ottawa, Ontario, Canada
Background

Multiple myeloma (MM) frequently presents as an unexplained decline in kidney function. Nephrologists often assess for discordance between the urine protein-creatinine ratio (UPCR) and urine albumin-creatinine ratio (UACR) as a proxy for free light chains in the urine consistent with cast nephropathy. However, thresholds for the urine protein-albumin gap (UPCR-UACR) and its association with MM are not well established.

Methods

We conducted a population-level, retrospective cohort study of adults in Ontario, Canada with same day measurements of UPCR/UACR and without a history of MM between 2009-2021 (N=28,231) using provincial health data. Individuals were categorized by quartile of urine protein-albumin gap and stratified by UPCR (≤ or >50 mg/mmol). Multivariable Cox regression models estimated the association between the urine protein-albumin gap and MM.

Results

116 individuals were diagnosed with MM (0.4%) at a median time of 31 days. In the overall cohort, MM diagnoses increased with each successive quartile of urine protein-albumin gap (Fig. A). However, compared to Quartile 1 (≤9.3 mg/mmol), only Quartile 4 (>43.4 mg/mmol) was associated with a significantly higher risk for MM (HR 4.49 [95%CI 2.47-8.15]). Among individuals with a UPCR≤50 mg/mmol, no association was observed (Fig. B). In contrast, among individuals with a UPCR>50 mg/mmol, a higher urine protein-albumin gap was associated with a higher risk of MM (Q1 ≤34.2 mg/mmol: ref, Q2 34.3-57.5 mg/mmol: HR 1.98 [95%CI 0.59-6.62], Q3 57.6-111.8 mg/mmol: HR 3.94 [95%CI 1.29-11.97], and Q4 >111.8 mg/mmol: HR 10.97 [95%CI 3.85-31.25]; Fig. C).

Conclusion

The urine protein-albumin gap is associated with MM, predominantly when the UPCR is >50 mg/mmol and the urine protein-albumin gap exceeds ~50 mg/mmol. These results establish clinically meaningful thresholds for clinicians to utilize when interpreting discordance between UPCR and UACR values as a predictor of MM in cases of unexplained kidney dysfunction.