Case Report: Complement and infection susceptibility

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Diagnosis of common variable immunodeficiency (CVID)

Lennart Truedsson MD/PhD, Section of Microbiology, Immunology and Glycobiology, Dept of Laboratory Medicine, Lund University, Lund, Sweden

Case Presentation

A female 25-year-old student is suffering from recurrent upper respiratory tract infections. She has had pneumonia 3 times during the last 5 years. Six months ago she was diagnosed with autoimmune thyroiditis. Her mother has selective IgA deficiency and two cousins have celiac disease. Now she has problems to keep up with her studies due to frequent infections and she is also chronically fatigued.

Evaluation and Diagnosis

The thyroid substitution therapy was checked and found to be adequate. Further analysis of the immune system included complement and immunoglobulins. Analysis of complement function with the Complement system screen Wieslab® showed normal activity for all the three activation pathways (classical, alternative and lectin). Measurement of immunoglobulin revealed low levels of two IgG subclasses, IgG1 and IgG2. Also IgA level was very low, below the level for IgA deficiency (0.07 g/L) but IgM was present in normal concentration. The final diagnose became common variable immunodeficiency (CVID).

Discussion and Conclusion

The symptoms of increased susceptibility for infections may have many different causes and among these are complement deficiencies. To analyze complement function is an elegant way to check for this possibility. When all pathways show normal activity as in this case, the suspicion of complement deficiency can be ruled out and the diagnostic could focus on other explanations.


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