Clinician perspectives on inpatient cystatin C utilization: A qualitative case study at Mayo Clinic

Establishing discordance rate of estimated glomerular filtration rate between serum creatinine-based calculations and cystatin-C-based calculations in critically ill patients

INTRODUCTION

The use of serum creatinine (SCr) for drug dosing has significant limitations and is influenced by many non-kidney factors. Cystatin C (cysC) is an alternative or additional marker of kidney function that is less affected by non-kidney factors. Although cysC may be useful in hospitalized patients, the use of cysC to calculate drug dosing in critically ill patients has been incompletely investigated.

OBJECTIVE

The objective of this study was to determine the rate of discordance in estimated glomerular filtration rate (eGFR) between SCr-based calculations and SCr/cysC-based calculations that affect drug dosing in critically ill patients.

METHODS

This was a single-center, retrospective, observational cohort study at an academic medical center including critically ill adult patients admitted in 2023 with SCr and cysC ordered. Data were collected via chart review. Demographic data were analyzed via descriptive statistics. Discordance, defined as the percentage of times at which there is at least one discrepancy in kidney dosing for a medication using Cockcroft-Gault (CG) creatinine clearance versus Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) eGFR creatinine-cystatin C (eGFRcr-cys) equations, was analyzed via Wilcoxon matched pair signed ranked sum. eGFR calculations were normalized for patients' body surface area for comparison.

RESULTS

The study population included 232 patients (53.02% female; mean age 58.7 +/- 14.9 years; with 62.5% in medical, 23.28% in surgical, and 8.62% in neurological intensive care) with a median SCr of 0.94 mg/dL IQR [0.57-1.58] and median cysC of 1.92 mg/L IQR [1.27-2.77]. The median clearance rates were 68.5 mL/min (45.3-111.5) for CG and 53.9 mL/min (30.9-80.7) for CKD-EPI eGFRcr-cys; p < 0.001. The discordance rate across all study drugs was 32.3% (75/232). The four most common study drugs demonstrating discordance were cefepime 40.6% (52/128), vancomycin 38.3% (46/120), levetiracetam 35.1% (13/37), and piperacillin/tazobactam 11.6% (5/43).

CONCLUSION

Clinically significant discordance exists between SCr and SCr/cysC-based estimates of kidney function. This study established a discordance rate, as defined by drug dosing, of 32.3% in adult patients admitted to the ICU.

Challenges and Perspectives on the Adoption of Cystatin C testing in China: A laboratory technician's perspective

Cystatin C (CysC) belongs to the cysteine protease inhibitor superfamily and is produced by all nucleated cells in the body in very stable amounts independent of age, sex, diet, and muscle mass. CysC is considered an ideal biomarker for assessing glomerular filtration rate (GFR) compared to traditional biomarkers for assessing GFR, such as creatinine. However, CysC is not sufficiently utilized for GFR assessment by clinicians, probably for various reasons such as insufficient understanding among clinicians or a lack of standardized quantitative methods. This review discusses and analyzes the aforementioned issues from the perspective of laboratory technicians.

Challenges in renally eliminated medication use: Evaluating cystatin C and serum creatinine eGFR discordance

BACKGROUND

Accurately estimating glomerular filtration rate (GFR) is crucial for dosing medications in hospitalized patients. Due to limitations of serum creatinine for GFR estimation, serum cystatin C (CysC) has been explored as an alternative functional kidney biomarker. This study assessed discordance between eGFRCr and eGFRCysC in a large sample of hospitalized patients and examined the frequency of renally eliminated medications affected by eGFR discordance.

METHODS

This multisite historical study included adults hospitalized between 2011 and 2023 with CysC and serum creatinine reported within 24 h of each other. The first concurrent biomarker pair for each patient was analyzed. eGFR discordance and use of renally eliminated medications were described.

RESULTS

17,718 hospitalized patients with concurrent creatinine and CysC assessments were included. The median eGFRCr was 65 mL/min, and the eGFRCysC was 46 mL/min. The median absolute difference of eGFRCr-eGFRCysC was 15 mL/min, and 7972 patients (45%) had a > 30% absolute difference. There was a significantly greater percentage of patients with an eGFR <30 mL/min based on eGFRCysC (26%) compared to eGFRCr (15%) (p < 0.001). Patients were prescribed an average of 20 medications in the 24 h surrounding the concurrent biomarker assessment. Renally eliminated medications accounted for 39% ± 13% of medication orders, and 80% of patients with eGFR discordance were prescribed five or more renally eliminated medications.

CONCLUSION

Substantial eGFR discordance between eGFRCysC and eGFRCr was observed in hospitalized patients, which directly affects the dosing of renally eliminated medications. Further research is needed to optimize the pharmacotherapy of renally eliminated medications with discordant GFR assessments to improve medication safety and effectiveness.

Cystatin C as a Marker of Kidney Function in Children

This review examines the reliability of cystatin C as a biomarker for kidney function in paediatric populations. Chronic kidney disease (CKD) affects a significant number of children globally, leading to severe health complications such as anaemia, hypertension, and growth disorders. Traditionally, kidney function has been assessed using the estimated glomerular filtration rate derived from serum creatinine, though this method is flawed due to variability in muscle mass, age, gender, and diet. Cystatin C offers an alternative as it is less influenced by these factors. Evidence from various studies indicates that cystatin C provides a more accurate assessment of kidney function, especially in neonates and children with urinary tract malformations. Additionally, it is more reliable in early detection of acute kidney injury in paediatric intensive care units. Despite its potential, cystatin C is not yet widely adopted in clinical guidelines, primarily due to a lack of large-scale paediatric studies. Nonetheless, existing research supports its utility in providing a consistent and precise measure of kidney function across different paediatric age groups, suggesting that it could enhance early diagnosis and management of CKD in children if more extensive validation studies are conducted.

Drug stewardship in chronic kidney disease to achieve effective and safe medication use

People living with chronic kidney disease (CKD) often experience multimorbidity and require polypharmacy. Kidney dysfunction can also alter the pharmacokinetics and pharmacodynamics of medications, which can modify their risks and benefits; the extent of these changes is not well understood for all situations or medications. The principle of drug stewardship is aimed at maximizing medication safety and effectiveness in a population of patients through a variety of processes including medication reconciliation, medication selection, dose adjustment, monitoring for effectiveness and safety, and discontinuation (deprescribing) when no longer necessary. This Review is aimed at serving as a resource for achieving optimal drug stewardship for patients with CKD. We describe special considerations for medication use during pregnancy and lactation, during acute illness and in patients with cancer, as well as guidance for the responsible use of over-the-counter drugs, herbal remedies, supplements and sick-day rules. We also highlight inequities in medication access worldwide and suggest policies to improve access to quality and essential medications for all persons with CKD. Further strategies to promote drug stewardship include patient education and engagement, the use of digital health tools, shared decision-making and collaboration within interdisciplinary teams. Throughout, we position the person with CKD at the centre of all drug stewardship efforts.

An LC-MS/MS method for serum cystatin C quantification and its comparison with two commercial immunoassays

OBJECTIVES

The standardization of cystatin C (CysC) measurement has received increasing attention in recent years due to its importance in estimating glomerular filtration rate (GFR). Mass spectrometry-based assays have the potential to provide an accuracy base for CysC measurement. However, a precise, accurate and sustainable LC-MS/MS method for CysC is still lacking.

METHODS

The developed LC-MS/MS method quantified CysC by detecting signature peptide (T3) obtained from tryptic digestion. Stable isotope labeled T3 peptide (SIL-T3) was spiked to control matrix effects and errors caused by liquid handling. The protein denaturation, reduction and alkylation procedures were combined into a single step with incubation time of 1 h, and the digestion lasted for 3.5 h. In the method validation, digestion time-course, imprecision, accuracy, matrix effect, interference, limit of quantification (LOQ), carryover, linearity, and the comparability to two routine immunoassays were evaluated.

RESULTS

No significant matrix effect or interference was observed with the CysC measurement. The LOQ was 0.21 mg/L; the within-run and total imprecision were 1.33-2.05 % and 2.18-3.90 % for three serum pools (1.18-5.34 mg/L). The LC-MS/MS method was calibrated by ERM-DA471/IFCC and showed good correlation with two immunoassays traceable to ERM-DA471/IFCC. However, significant bias was observed for immunoassays against the LC-MS/MS method.

CONCLUSIONS

The developed LC-MS/MS method is robust and simpler and holds the promise to provide an accuracy base for routine immunoassays, which will promote the standardization of CysC measurement.

Comparison of Cystatin C and Creatinine in the Assessment of Measured Kidney Function during Critical Illness

BACKGROUND

Incomplete recovery of kidney function is an important adverse outcome in survivors of critical illness. However, unlike eGFR creatinine, eGFR cystatin C is not confounded by muscle loss and may improve identification of persistent kidney dysfunction.

METHODS

To assess kidney function during prolonged critical illness, we enrolled 38 mechanically ventilated patients with an expected length of stay of >72 hours near admission to intensive care unit (ICU) in a single academic medical center. We assessed sequential kidney function using creatinine, cystatin C, and iohexol clearance measurements. The primary outcome was difference between eGFR creatinine and eGFR cystatin C at ICU discharge using Bayesian regression modeling. We simultaneously measured muscle mass by ultrasound of the rectus femoris to assess the confounding effect on serum creatinine generation.

RESULTS

Longer length of ICU stay was associated with greater difference between eGFR creatinine and eGFR cystatin C at a predicted rate of 2 ml/min per 1.73 m 2 per day (95% confidence interval [CI], 1 to 2). By ICU discharge, the posterior mean difference between creatinine and cystatin C eGFR was 33 ml/min per 1.73 m 2 (95% credible interval [CrI], 24 to 42). In 27 patients with iohexol clearance measured close to ICU discharge, eGFR creatinine was on average two-fold greater than the iohexol gold standard, and posterior mean difference was 59 ml/min per 1.73 m 2 (95% CrI, 49 to 69). The posterior mean for eGFR cystatin C suggested a 22 ml/min per 1.73 m 2 (95% CrI, 13 to 31) overestimation of measured GFR. Each day in ICU resulted in a predicted 2% (95% CI, 1% to 3%) decrease in muscle area. Change in creatinine-to-cystatin C ratio showed good longitudinal, repeated measures correlation with muscle loss, R =0.61 (95% CI, 0.50 to 0.72).

CONCLUSIONS

eGFR creatinine systematically overestimated kidney function after prolonged critical illness. Cystatin C better estimated true kidney function because it seemed unaffected by the muscle loss from prolonged critical illness.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Skeletal Muscle Wasting and Renal Dysfunction After Critical Illness Trauma - Outcomes Study (KRATOS), NCT03736005 .

AACC/NKF Guidance Document on Improving Equity in Chronic Kidney Disease Care

BACKGROUND

Kidney disease (KD) is an important health equity issue with Black, Hispanic, and socioeconomically disadvantaged individuals experiencing a disproportionate disease burden. Prior to 2021, the commonly used estimated glomerular filtration rate (eGFR) equations incorporated coefficients for Black race that conferred higher GFR estimates for Black individuals compared to non-Black individuals of the same sex, age, and blood creatinine concentration. With a recognition that race does not delineate distinct biological categories, a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended the adoption of the CKD-EPI 2021 race-agnostic equations.

CONTENT

This document provides guidance on implementation of the CKD-EPI 2021 equations. It describes recommendations for KD biomarker testing, and opportunities for collaboration between clinical laboratories and providers to improve KD detection in high-risk populations. Further, the document provides guidance on the use of cystatin C, and eGFR reporting and interpretation in gender-diverse populations.

SUMMARY

Implementation of the CKD-EPI 2021 eGFR equations represents progress toward health equity in the management of KD. Ongoing efforts by multidisciplinary teams, including clinical laboratorians, should focus on improved disease detection in clinically and socially high-risk populations. Routine use of cystatin C is recommended to improve the accuracy of eGFR, particularly in patients whose blood creatinine concentrations are confounded by processes other than glomerular filtration. When managing gender-diverse individuals, eGFR should be calculated and reported with both male and female coefficients. Gender-diverse individuals can benefit from a more holistic management approach, particularly at important clinical decision points.

Advantages, Limitations, and Clinical Considerations in Using Cystatin C to Estimate GFR

Cystatin C has been shown to be a reliable and accurate marker of kidney function across diverse populations. The 2012 Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommended using cystatin C to confirm the diagnosis of chronic kidney disease (CKD) determined by creatinine-based estimated glomerular filtration rate (eGFR) and to estimate kidney function when accurate eGFR estimates are needed for clinical decision-making. In the efforts to remove race from eGFR calculations in the United States, the National Kidney Foundation (NKF) and American Society of Nephrology (ASN) Joint Task Force recommended increasing availability and clinical adoption of cystatin C to assess kidney function. This review summarizes the key advantages and limitations of cystatin C use in clinical practice. Our goals were to review and discuss the literature on cystatin C; understand the evidence behind the recommendations for its use as a marker of kidney function to diagnose CKD and risk stratify patients for adverse outcomes; discuss the challenges of its use in clinical practice; and guide clinicians on its interpretation.