In patients with systemic lupus erythematosus, which laboratory finding indicates nephritis flare?

Elevated anti-dsDNA antibodies are a significant indicator of disease activity in systemic lupus erythematosus, particularly concerning nephritis flares. When a patient's lupus is active, especially in the context of renal involvement, the titers of anti-dsDNA often rise. This is because the production of these antibodies correlates with the inflammatory processes taking place in the body, including those affecting the kidneys. Thus, an increase in anti-dsDNA serves as a useful laboratory marker to assess for an exacerbation of lupus nephritis.

In the context of other options, low creatinine would generally suggest preserved kidney function and is not indicative of a flare. High protein levels may suggest renal compromise, but they are not as specific to lupus nephritis flares compared to elevated anti-dsDNA. Low calcium levels can occur due to various reasons but do not specifically relate to lupus nephritis activity. Therefore, elevated anti-dsDNA antibodies provide the most specific insight into a potential nephritis flare in patients with systemic lupus erythematosus.