RESUMO
Complement proteins are important in humoral immunity. In the hospital setting, complement component 3 [C3] and 4 [C4] are requested to determine the etiology of certain illnesses in addition to monitoring disease activity, particularly systemic lupus erythematosus [SLE]. The aim of this study was to evaluate the correlation between C3 and C4, and to evaluate the significance of ordering both tests in patients with SLE during follow up. Retrospective review King Abdul-Aziz University Hospital, Jeddah, Saudi Arabia Complement levels were evaluated over a six month period [January 1, 2009 - June 30, 2009]. Patient's sera were classified into three groups: Group I with SLE, Group II with rheumatoid arthritis [RA] and Group III with other rheumatological and non-rheumatological disorders. Intervention: Serum level test Main Outcome Measure: The correlation between C3 and C4 One hundred and one [101] blood requests for C3 and C4 were evaluated. C4 hypocomplementemia was detected in 47/60 patients [78.3%], 9/16 patients [56.3%] and 1/25 patient [4.4%] in Groups I, II and III respectively. This was in contrast to C3 hypocomplementemia which was detected in 21/60 patients [35%], 3/16 patients [18.8%] and 1/25 patient [4%] in Groups I, II and III respectively. There was a simple linear regression between C3 and C4 level [p < 0.001]. C4 hypocomplementemia is more frequently found than C3 hypocomplementemia in SLE patients. A correlation exists between the two tests, suggesting the adequacy of ordering a single test [C4] for the purpose of cost effectiveness