Acquired C1 Esterase Inhibitor Deficiency

TO THE EDITOR:

Markovic and colleagues have written an excellent review on angioedema due to acquired C1 esterase inhibitor deficiency (1). However, from a practical standpoint, their proposal for diagnostic work-up in patients with angioedema of unknown cause is of concern: It is time-consuming and expensive to test three complement proteins before determinations of C1 esterase inhibitor activity in patients with suspected angioedema. In addition, C3 and C4 levels may be within normal limits during symptom-free intervals. Therefore, if the algorithm provided is used, some patients may be misdiagnosed. It seems more feasible to first determine C1 esterase inhibitor activity, which may detect nearly all types of C1 esterase inhibitor deficiency, as stated by Markovic and colleagues. If activity is within normal limits, no further laboratory tests are necessary. If activity is low (<70%), quantitative determination of C1 esterase inhibitor protein and C1q will establish the correct diagnosis. This work-up is more convenient to both patient and physician, especially in the outpatient setting. Laboratory costs and time to diagnosis will be reduced by nearly 50% compared to the approach outlined by Markovic and colleagues. Medical practice should always be guided by pathophysiologic considerations but must also rely on quick and proper diagnostic work-up. Academic approaches should not delay diagnosis or therapy.