Creatinine clearance measures the rate at which the kidneys filter creatinine, a waste product of muscle metabolism, from the blood.  It is an important indicator of kidney function and helps in the diagnosis and management of kidney disease. Creatinine clearance is used to estimate the Glomerular Filtration Rate (GFR), which is a key measure of how well the kidneys are filtering blood. 

Decreased creatinine clearance is a hallmark of Chronic Kidney Disease (CKD) and helps in staging the disease. In cases of acute kidney injury, creatinine clearance can help assess the extent of renal impairment. Many medications, such as antibiotics and chemotherapeutic agents, are cleared through the kidneys. Adjusting drug dosages based on creatinine clearance is critical in preventing toxicity in patients with impaired renal function.