The complement system is an important part of the innate immune response and plays a key role in the defence against invading pathogens, including viruses, bacteria, fungi, and parasites. Recent studies have shown that complement overactivation plays a critical role in the pathogenesis of COVID-19 and other viral diseases, suggesting its huge potential as a biomarker for infectious diseases. Being able to accurately measure how, where, and why the complement system is activated is ess