It is not possible to generalize whether low complement C1q is serious. Low complement C1q is commonly found in systemic lupus erythematosus, lupus nephritis, mixed connective tissue disease, infectious diseases, tumors and so on. Whether low complement C1q is serious or not needs to be judged according to a combination of factors. Complement C1q is an important component that makes up complement C1 and initiates the classical activation pathway of complement. Complement C1q can be decreased in systemic lupus erythematosus, lupus nephritis, and mixed connective tissue disease; sometimes infectious diseases and tumors can also cause decreased complement C1q. A low complement C1q level does not directly determine the severity of the disease. The assessment of the severity of the disease is not determined by simply considering one indicator of the laboratory examination, but by a comprehensive judgment based on a number of factors. If you have a low complement C1q, you need to consult a hospital in time to determine the cause of the low level and assess the severity of the disease based on the cause of the disease, the condition of the patient, and the relevant indicators of the examination, and comply with the doctor’s instructions for treatment.