Which statement about complement C3 levels is typical during a systemic lupus erythematosus flare?

Which statement about complement C3 levels is typical during a systemic lupus erythematosus flare?

• A. C3 decreases during a flare
• B. C3 increases during a flare
• C. C3 remains unchanged during a flare
• D. C3 fluctuates unpredictably during a flare

Answer: (A)

During a systemic lupus erythematosus flare, immune complexes activate the classical complement pathway, which consumes C3. This leads to lower serum C3 levels, a pattern commonly seen with active disease and often accompanying lupus nephritis. As the flare abates and immune complex formation decreases, C3 can rise again. So, the typical finding is a decrease in C3 during a flare. The other possibilities don’t fit the mechanism: an increase would imply less consumption or more production, unchanged levels ignore ongoing activation, and unpredictable fluctuation isn’t characteristic of the disease’s inflammatory-driven consumption.

During a systemic lupus erythematosus flare, immune complexes activate the classical complement pathway, which consumes C3. This leads to lower serum C3 levels, a pattern commonly seen with active disease and often accompanying lupus nephritis. As the flare abates and immune complex formation decreases, C3 can rise again. So, the typical finding is a decrease in C3 during a flare. The other possibilities don’t fit the mechanism: an increase would imply less consumption or more production, unchanged levels ignore ongoing activation, and unpredictable fluctuation isn’t characteristic of the disease’s inflammatory-driven consumption.