If one wanted an alternative to creatinine for evaluating GFR, which marker would be used?

Prepare for the Clinical Chemistry and Pathologic of Biochemistry Exam with comprehensive questions, detailed explanations, and effective study strategies. Ace your test with confidence!

Cystatin C is used as an alternative marker for estimating GFR because it is produced by all nucleated cells at a constant rate and is freely filtered by the glomerulus with minimal to no tubular secretion. Its serum level tracks changes in filtration rate more consistently than creatinine in some populations, since it is less dependent on muscle mass, age, or diet. This makes it particularly useful when creatinine-based estimates may be biased, such as in people with abnormal muscle mass or malnutrition. There are formulas that use cystatin C (and sometimes combine it with creatinine) to estimate GFR, which can improve accuracy in these cases. However, cystatin C can be influenced by factors like inflammation, obesity, thyroid function, and certain medications, so it isn’t perfect in all situations. The other substances listed—plasma urea (BUN), uric acid, and potassium—are affected by non-renal factors (protein intake and liver function for BUN; purine intake and excretion for uric acid; electrolyte balance and renal handling for potassium) and are not reliable standalone markers for estimating GFR.