In outpatient primary care settings, would you recommend routinely checking Cystatin-C as a marker of renal function in older adults?

I probably would not recommend routine Cystatin-C testing for all older adults, but would consider it in certain scenarios where eGFR may be inaccurate or misleading. In geriatrics, sarcopenia and low muscle mass often make serum creatinine a less reliable marker of true kidney function. Cystatin-C can be helpful when the eGFR will affect management (such as medication dosing), borderline eGFR values, or when creatinine-based estimates don’t fit the clinical context. For many patients, a combined creatinine + Cystatin-C eGFR provides the most accurate assessment. But a screening tool for all community-dwelling older adults would not be cost-effective and unlikely necessary unless it would change care.

When Cystatin-C may be useful:

• Frailty...

There isn't much literature guidance for this question. In general, I don't think we're at the point of using this as routine testing. Rather, I think it is useful in certain clinical situations, such as eGFR at the border of CKD staging or symptoms that seem out of proportion for eGFR, particularly if the patient has low muscle mass.

I have a Geriatric Nephrology clinic primarily populated by patients over 80 years old with CKD 3B-5. A few years ago, Cystatin C became readily available at my institution, and I have been checking it more frequently in this group of patients. I have yet to systematically review results, but it seems that there is more discordance at higher levels of eGFR and less discordance at lower levels of eGFR. There ha...

One more piece to the story - Estrella et al., PMID 41202182.