RESUMO
OBJECTIVE: To develop a method for determining the concentration of the third component of complement (C3) in canine serum, to establish a reference range for C3 in healthy dogs, and to evaluate dogs with protein-losing nephropathy (PLN) to determine whether PLN is associated with decreased serum C3 concentrations. ANIMALS: 30 healthy dogs and 49 dogs with PLN. PROCEDURES: Serum samples were obtained from healthy dogs at the time of examination, whereas serum samples were obtained from dogs with PLN at the time of diagnosis. All samples were frozen at -70 degrees C until analyzed. Serum C3 concentrations were determined by use of a sandwich ELISA. Concentrations were expressed as the number of dilutions in which C3 could be detected. RESULTS: C3 was detectable in healthy control dogs (range, 1,920,000 to 15,400,000 dilutions; median, 9,600,000 dilutions). This represented a range of four 2-fold serum dilutions. In addition, C3 was detectable in dogs with PLN (range, 1,460,000 to 30,070,000 dilutions; median, 7,680,000 dilutions), which represented a range of six 2-fold serum dilutions. There was no significant difference in C3 concentrations between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE: C3 is a critical part of the immune defense system that has not been extensively examined in veterinary medicine. An ELISA was developed for measuring C3 concentrations, and a reference range for healthy dogs was established. Significant decreases in C3 concentrations were not detected in any dog with PLN. Additional studies will be required to definitively determine the importance of serum C3 concentrations in PLN.