We have set reference ranges for future applications, and our first proof-of-concept study showed that levels of both markers are increased in COVID-19, suggesting that C1-INH complex measurements might have added value for investigating and unravelling early CP and LP activation in other human diseases where complement is involved, such as SLE, HAE, Sepsis as well as other viral, bacterial and fungal infections. This evidence concerns the gene SERPING1 and systemic lupus erythematosus.