Accurate assessment of kidney function is essential in hospitalized patients. However, serum creatinine does not always reflect true kidney function because it can be influenced by factors such as muscle mass, diet, and medications. When creatinine-based estimates are unreliable, cystatin C may serve as a useful complementary marker for internists. Compared with creatinine, cystatin C is less affected by these factors and may respond more rapidly to changes in glomerular filtration, which can improve recognition of kidney dysfunction and help refine chronic kidney disease (CKD) staging in hospitalized patients.
