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Falsely Elevated Plasma Creatinine Due to an Immunoglobulin M Paraprotein
Mitchell R McGill1, Anitha Vijayan2, Elbert P Trulock3
1Division of Laboratory and Genomic Medicine, Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO.
Summary
Enzymatic creatinine tests can yield falsely high results due to monoclonal immunoglobulin M (IgM) paraproteins. This interference, identified in a lung transplant patient, impacts accurate kidney function assessment.
Area of Science:
- Clinical Chemistry
- Immunology
- Nephrology
Background:
- Plasma creatinine measurement is crucial for assessing kidney function.
- Traditional picric acid methods are common, but enzymatic assays offer improved specificity.
- Accurate creatinine levels are vital for patient management, especially in transplantation evaluations.
Observation:
- A patient undergoing lung transplant evaluation exhibited falsely elevated plasma creatinine levels (1.54-1.71 mg/dL) using the Roche Creatinine plus enzymatic assay.
- Picric acid-based and other enzymatic methods yielded significantly lower, accurate creatinine values (0.7-0.8 mg/dL).
- Serum protein electrophoresis identified an IgM kappa light chain paraprotein as the interfering substance.
Findings:
- The elevated creatinine levels were directly attributed to the presence of a monoclonal immunoglobulin M (IgM) paraprotein.
- Ultrafiltration removing proteins >30kDa normalized the creatinine levels in the Roche assay.
- Adding the patient's immunoglobulin fraction to normal plasma mimicked the interference, confirming the role of IgM paraprotein.
Implications:
- This case highlights potential interference in enzymatic creatinine assays by specific paraproteins, particularly IgM.
- Clinical laboratories should be aware of this interference to avoid misdiagnosis and inappropriate patient management.
- Further investigation into assay interferences by monoclonal proteins is warranted for improved diagnostic accuracy.
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