Which lab value is a key indicator of renal function in a client with SLE?

Serum creatinine is a key indicator of renal function because it is a waste product produced from muscle metabolism, and its levels in the blood reflect how well the kidneys are filtering out wastes from the bloodstream. In the context of systemic lupus erythematosus (SLE), which can lead to renal involvement (lupus nephritis), monitoring serum creatinine levels is crucial as they can rise when kidney function declines. An increased serum creatinine level typically indicates an impairment in the kidneys' ability to clear creatinine, signaling potential kidney damage or decreased glomerular filtration rate (GFR).

While blood urea nitrogen (BUN) can also indicate renal function, it is less specific than serum creatinine because BUN levels can be influenced by hydration status, protein intake, and liver function, among other factors. Serum sodium levels are not directly indicative of renal function, as sodium can be affected by various factors including hydration status and hormonal regulation. Urine-specific gravity provides information about kidney's ability to concentrate urine but does not serve as a definitive measure of overall renal function. Therefore, serum creatinine is the most reliable and direct indicator of renal function in patients with SLE.