Unexpected discovery of CRP analytical interference: A case report

Area of Science:

• Clinical Chemistry
• Immunology
• Laboratory Medicine

Background:

• Immunoturbidimetric assays are widely used in clinical diagnostics.
• These assays can be susceptible to analytical interferences, including matrix effects and high immunoglobulin concentrations.
• Such interferences can significantly impact the accuracy of measured analytes, such as C-reactive protein (CRP).

Observation:

• A 75-year-old patient with multiple chronic diseases presented with an unexpectedly high CRP plasma value (>700 mg/L).
• Despite the elevated CRP, the patient showed no clinical signs of infection, raising suspicion of assay interference.
• Initial investigation ruled out anti-mouse autoantibody interference, but further analysis revealed abnormal monoclonal immunoglobulins.

Findings:

• The high CRP levels were attributed to analytical interference caused by monoclonal immunoglobulins, not an actual infection or inflammatory response.
• Liquid immunoprecipitation assays for CRP were particularly affected, while solid phase immunochemistry assays showed no interference.
• Protein electrophoresis and immunofixation confirmed a lymphoma relapse and the presence of interfering monoclonal immunoglobulins.

Implications:

• Accurate interpretation of clinical biochemistry parameters like CRP requires awareness of potential analytical interferences.
• High immunoglobulin levels, particularly monoclonal immunoglobulins, can lead to falsely elevated CRP results.
• Close collaboration between laboratory professionals and clinicians, alongside comprehensive review of patient data, is crucial for correct diagnosis and management.