The serine protease complement factor D is fundamental in the activation of the complement system. In addition, it was the first adipokine described (named Adipsin) and shown to improve beta cell function in diabetes. As part of an amplification loop of complement activation, factor D is a rate-limiting enzyme, and its accessibility contributes to the potency of complement activation. The dogma has been that conversion of the zymogen form, profactor D, to mature factor D occurred during secretion by adipocytes by uncharacterized proteases. However, recent findings demonstrated that the serine protease MASP-3 of the lectin pathway of the complement system mediated this conversion, suggesting that pattern recognition of pathogen/danger-associated molecular patterns could be a prior requirement for all complement activation. To facilitate studies addressing this hypothesis, we have developed monoclonal antibodies specific for human profactor D without binding to mature factor D. We demonstrate their applications in accessing the conversion of profactor D into mature factor D and in measuring levels of profactor D.