Serum complement determinations in patients with quiescent systemic lupus erythematosus

To determine whether complement component analyses during a period of inactive disease can define clinically important subgroups and predict morbidity in patients with systemic lupus erythematosus (SLE).

We identified 277 patients with SLE whose disease became clinically inactive at some point after diagnosis. Serum samples were obtained at that time and tested for total complement activity (CH100) and antigenic levels of C1q, C1r, C1s, C3 and C4. Results of complement determinations were correlated with demographic characteristics and clinical findings in the followup period (mean observation period 4.25 years).

We identified 25 (9%) patients with multiple complement determinations below the normal range. 24 other patients (8.5%) had a very low level of a single complement component. The group with multiple complement determinations below the normal range was much more likely than the normocomplementemic SLE controls to progress to renal insufficiency. In other respects, complement component determinations were neither reflective nor predictive of clinical course.

In this group of patients with inactive SLE, complement component analyses did not generally correlate with longterm outcome; however, multiple low complement component determinations during disease quiescence was associated with increased risk of renal insufficiency.