A 16 year old patient came to my office because of an apparently unprovoked episode of angioedema involving upper lip and right hand. He also reported slight abdominal pain. I see the patient approximately 1 hour after onset and he states that the edema is slowly subsiding. No urticaria present. Labs done at that moment were normal but did not include C3, C4 or C1 esterase/inhibitor levels. These were done a month later and were as follows:
C3 149 mg/dL (90-180)
C4 27 mg/dL (10-40)
C1q esterase inhibitor 134 mg/L (154-351)

Is this low C1 esterase inhibitor significant? I know that we must obtain levels during the attack but it was impossible in this case. What would be the next best strategy if the patient has not had any other episodes?


Thank you for your inquiry.

These values certainly do not exclude the diagnosis of C1 inhibitor deficiency syndrome. However, the normal level of C4 certainly mitigates against this diagnosis. However, as you mentioned, C4 can be normal between attacks. Thus because you have not excluded a diagnosis of C1 inhibitor deficiency entirely, I would suggest the following:

1. If the C1 inhibitor assay was not done using a chromogenic assay, I would remeasure the level using the chromogenic method. This can be obtained from the National Jewish Complement Laboratory. For your convenience, the contact information is copied below:

National Jewish Complement Laboratory
Director: Patricia C. Giclas, PhD
Assistant Director: Ashley Frazer-Abel, PhD
Laboratory: 303.398.1541

2. As you suggested, I would repeat assays of complement again during an episode.

Until at least the chromogenic assay is done, I do not think that we can feel secure as to the diagnosis (idiopathic angioedema versus C1 inhibitor deficiency syndrome). As you know, making a distinction between these two forms of angioedema is crucial because it would affect the therapy.

Thank you again for your inquiry and we hope this response is helpful to you. If you have further questions after these tests are performed, we would be happy to hear from you again.

Phil Lieberman, M.D.

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