Which two endogenous markers are used to estimate glomerular filtration rate?

• A. Cystatin C and Beta-trace protein
• B. Creatinine and Urea
• C. Cystatin C and Creatinine
• D. Beta-trace protein and Urea

Answer: (A)

Estimating GFR relies on substances produced inside the body and cleared by the kidneys, with the best accuracy come from using two endogenous markers that reflect filtration while having different nonrenal influences. The two most widely used are creatinine and cystatin C. Creatinine comes from muscle metabolism and, when filtered by the glomerulus, its blood level rises as GFR falls. However, its value is affected by muscle mass, age, sex, and diet, which can blur the GFR picture. Cystatin C is produced at a fairly constant rate by all nucleated cells and is freely filtered; it is less dependent on muscle mass and diet, though it can be influenced by inflammation and other conditions. When these two markers are used together in equations, they offset each other’s limitations and yield a more precise GFR estimate than either marker alone.

Urea can increase with reduced GFR but is also strongly influenced by protein intake, hydration, and liver function, making it a less reliable standalone estimator of GFR. Beta-trace protein has been explored as an additional marker, but it is not as universally adopted as creatinine and cystatin C for standard GFR estimation. That’s why creatinine and cystatin C are the two endogenous markers most commonly used to estimate GFR.