Can a recent COVID-19 infection and treatment with Paxlovid (nirmatrelvir/ritonavir) explain an elevated kappa light chain level?

COVID-19 Infection and Elevated Kappa Light Chain Levels

Yes, your recent COVID-19 infection can explain the elevated kappa light chain level of 28.8 mg/L (upper limit 19 mg/L) and slightly elevated kappa/lambda ratio of 1.83.

Relationship Between COVID-19 and Inflammatory Markers

COVID-19 infection is known to cause a hyperinflammatory state that affects multiple biomarkers in the body. The SARS-CoV-2 virus triggers a significant inflammatory response that can result in:

• Hyperinflammatory status or cytokine storm induced by SARS-CoV-2 infection 1
• Elevated inflammatory markers including various proteins and immunoglobulins
• Activation of the NF-κB pathway, which is involved with inflammation and is shown to be elevated in response to coronaviruses 2

Interpretation of Your Laboratory Findings

Your laboratory findings show:

• Elevated kappa light chain level (28.8 mg/L, upper limit 19 mg/L)
• Slightly elevated kappa/lambda ratio (1.83)
• No M-spike
• Normal SPEP (Serum Protein Electrophoresis)
• Normal CBC, sed rate and CRP

This pattern is consistent with a polyclonal immune response rather than a monoclonal gammopathy. The absence of an M-spike and normal SPEP are particularly reassuring, as these would typically be abnormal in monoclonal gammopathies like multiple myeloma.

COVID-19 and Immune System Response

During COVID-19 infection, the immune system produces various proteins, including:

1. Inflammatory cytokines
2. Acute phase reactants
3. Immunoglobulins (antibodies) with both heavy and light chains

The production of these antibodies can lead to a temporary elevation in free light chains, particularly during the recovery phase when your body is actively producing antibodies against the virus.

Timeline Considerations

The fact that you had COVID-19 in mid-June and completed Paxlovid treatment is significant. Studies show that:

• Nirmatrelvir-ritonavir (Paxlovid) affects viral clearance and can influence the immune response 3
• The immune response to COVID-19 can persist for weeks after the acute infection
• At age 70, immune responses may take longer to normalize after infection

Monitoring Recommendations

Given your clinical scenario, I recommend:

1. Repeat testing in 3-6 months to see if the kappa light chain level normalizes
2. No immediate additional workup is needed given the normal SPEP, absence of M-spike, and normal CBC
3. Monitor for any new symptoms such as bone pain, fatigue, recurrent infections, or anemia

When to Be Concerned

You should seek further evaluation if:

• Kappa light chain levels continue to rise on repeat testing
• An M-spike develops on future SPEP testing
• You develop symptoms concerning for a plasma cell disorder
• Other abnormalities develop in your CBC or kidney function

Conclusion

The pattern of isolated elevated kappa light chains without other concerning findings, in the setting of recent COVID-19 infection, is most consistent with a reactive process due to your recent viral infection rather than a concerning hematologic disorder. The use of Paxlovid may have influenced your immune response as well, as it affects viral clearance and potentially the subsequent immune response 3.