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Kidney Week

Abstract: PO1906

Will the Real Creatinine Please Stand Up? Elevated Creatinine in a Patient with Smoldering Myeloma

Session Information

Category: Onco-Nephrology

  • 1500 Onco-Nephrology

Author

  • Zeitler, Evan, UNC Kidney Center, Chapel Hill, North Carolina, United States
Introduction

Monoclonal gammopathies cause altered kidney function by a variety of mechanisms. The assessment of patients with monoclonal proteins is further complicated by non-physiologic alterations in laboratory assays, including the assessment of serum creatinine, as reported in this case of a patient with smoldering myeloma.

Case Description

A 47 yo woman with a history of mixed connective tissue disease, hypertension, and IgG lambda light chain smoldering myeloma was referred for evaluation of creatinine of 1.6 mg/dL. Her medications were acebutolol, furosemide, hydrochlorothiazide and aspirin. Examination revealed BP 129/86, HR 60 without notable physical findings. Her laboratory evaluation was significant for a creatinine of 0.88 mg/dL, BUN of 10 mg/dL, albumin of 4.6 g/dL and total protein of 9.0 g/dL, with an M-spike of 1 g/dL. Her urine protein-creatinine ratio was 0.47 g/g creatinine.

Over the next year, creatinine at her primary oncologist ranged from 1.2-1.3 mg/dL (except for a single episode of acute kidney injury), while in the nephrology clinic the creatinine was 0.8-0.9 mg/dL. Further investigation determined that the external lab used a picric acid-based creatinine assay, while creatinine from the nephrology clinic was measured using an enzymatic method.

Discussion

Monoclonal proteins have previously been reported to interfere with creatinine assays, primarily in patients with Waldenstrom's macroglobulinemia. We report here a patient with a monoclonal IgG lambda paraprotein interfering with a Jaffe-based creatinine assay leading to pseudohypercreatininemia. Both nephrologists and oncologists should be aware of this phenomenon in the care of patients with all types of paraproteinemias, so that alternative means of kidney function assessment (such as measurement of cystatin c) can be employed when creatinine assays are unreliable.

Serum creatinine and kappa/lambda free light chain ratios