How do you approach evaluation of hypocomplementemia in a patient with arthralgias and a history of Hodgkin's lymphoma treated in the past?

There are both acquired disorders - more common - of the complement system and inherited disorders - less common - of the complement system. Although rheumatologists commonly deal with autoimmune/acquired disorders of the immune system, they should be aware that certain inherited deficiencies of the complement system, often early components of the classical pathway including C1q, C1r, C1s, C4, and C2, can lead to autoimmunity, particularly systemic lupus erythematosus (SLE). SLE is the prototypical disease we commonly think of when hypocomplementemia is detected and with an increased risk of both Hodgkins and non-Hodgkins lymphoma in SLE, certainly this would need to be considered and a careful history with appropriate serologic testing sho...