Reduced circulating complement concentration Decreased circulating C1q concentration 2023-03-12T18:06:12Z Concentration or activity of the C1q protein in the blood circulation below the lower limit of normal. C1q is the first component of the classical pathway and is composed of the C1qA chain, C1qB chain, and C1qC chain, which are encoded by C1qA, C1qB, and C1qC genes.