(1349) A Real-World Description of Medication Dose Adjustment Using Cystatin C in Critically Ill Adults

Introduction: In critically ill adults, renal function is typically assessed using serum creatinine. Assessment of estimated glomerular filtration rate (eGFR) using serum cystatin C values is an alternative option that may be superior to creatinine-based assessment in certain patient populations. This study describes the ability to use cystatin C to help optimize medication dosing in critically ill adults.

Methods: Adult patients admitted to an intensive care unit (ICU) at an academic medical center from January 2022 through May 2023 with a serum cystatin C level were included. Patients were assessed for medication renal dose adjustment within 48 hours of obtaining the first cystatin C level. There was no institutional protocol or guideline in place for cystatin C monitoring or medication dosing during this time. Institutional standards for medication dosing at the time recommended assessment of serum creatinine and the Cockcroft-Gault equation. The 2021 Chronic Kidney Disease Epidemiology (CKD-EPI) equation was used to calculate eGFR with cystatin C (eGFR-cysC).

Results: Serum cystatin C was collected in 138 patients. Cystatin C was most frequently obtained in the medical ICU (59.4%), although at least one Cystatin C was obtained in each ICU at the institution. Cystatin C was requested in a nephrology consult service note in 15.9% (22/138) of patients. A medication dose was adjusted in agreement with eGFR-cysC in 20.2% (28/138) of patients . Additionally, there were 18 (13%) patients in which there were opportunities for dose adjustment based on cystatin C eGFR but medication doses were not changed. Compared to patients with a BMI in ranging from 20-29.9, medication dose adjustments were more common in patients with a BMI less than 20 (9.6% vs. 23.3%, p=0.06) and BMI greater than 30 (9.6% vs. 38.2%, p< 0.01). All medications that were adjusted were antibiotics or antivirals.

Conclusions: Assessment of eGFR using cystatin C instead of serum creatinine alone in critically ill adults may identify opportunities for medication dose adjustment. Patients at the extremes of weight appear to be more likely to have discrepancies in eGFR when cystatin C is compared to serum creatinine. Further research is needed to understand optimal dosing regimens when discrepancies are known or suspected.