What is the best laboratory indicator of an acute exacerbation of Systemic Lupus Erythematosus (SLE)?

The best laboratory indicator of an acute exacerbation of Systemic Lupus Erythematosus (SLE) is a decrease in serum complement levels. In SLE, complement system proteins, particularly C3 and C4, are often consumed during active disease due to immune complex formation and inflammation. This consumption leads to decreased serum complement levels, reflecting ongoing disease activity and severity during exacerbations.

The decrease in complement levels correlates with disease flare-ups and is utilized in monitoring SLE, as it is associated with the development of specific manifestations such as lupus nephritis and other organ involvement. This makes it a reliable marker for assessing flare-ups in SLE patients.

In contrast, while increased serum creatinine may indicate renal involvement or damage, it is not specific for SLE exacerbations and can be influenced by other renal pathologies. An elevated white blood cell count can occur due to many conditions and is not exclusively indicative of SLE exacerbation. Increased platelets may be observed in various conditions but do not specifically reflect disease activity in SLE. Thus, the decrease in serum complement is the most specific and relevant indicator of an acute exacerbation in patients with SLE.