Final answer:
A creatinine clearance test measures kidney function by calculating the rate at which blood is cleared of creatinine. It helps ascertain the GFR, corrected for body surface area. Creatinine is a breakdown product of creatine phosphate, a quick energy source in muscles.
Step-by-step explanation:
A creatinine clearance test is a clinical procedure used to measure the glomerular filtration rate (GFR), which indicates how well the kidneys are filtering blood. The test involves calculating the volume of blood cleared of creatinine per minute based on concentrations of creatinine in the urine and blood, and the urine flow rate. The formula is Ccr = (Ux V) / B, where Ccr is the creatinine clearance rate, U is the urine creatinine concentration, V is the urine flow rate, and B is the blood creatinine concentration. To account for differences in body sizes, the values are often corrected for body surface area (BSA) and expressed as ml/min/1.73 m².
Creatinine is a waste product formed from the breakdown of creatine phosphate in muscle tissue. Creatine phosphate serves as a short-term energy source in muscle contractions, providing about 15 seconds worth of energy before another energy source is needed. This biochemical process is facilitated by the enzyme creatine kinase. For a 24-hour urine collection, normal ranges for creatinine clearance are 90-139 ml/min for adult males under 40 and 80-125 ml/min for adult females under 40. As a person ages, the GFR typically decreases.