Concordance between creatinine- and cystatin C-based eGFR in clinical practice

Difference Between Estimated GFR Based on Cystatin C Versus Creatinine and Incident Atrial Fibrillation: A Cohort Study of the UK Biobank

RATIONALE & OBJECTIVE

The difference between cystatin C-based and creatinine-based estimated glomerular filtration rate (eGFRdiff) has been suggested to reflect factors distinct from kidney function that are associated with cardiovascular risk. However, the association between eGFRdiff and atrial fibrillation (AF) risk has not been extensively evaluated.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

Using data from the UK Biobank, this study included 363,494 participants with measured serum creatinine and cystatin C levels and without a prior diagnosis of AF or a history of related procedures.

EXPOSURE

Estimated GFRdiff, calculated as cystatin C-based eGFR minus creatinine-based eGFR. Estimated GFRdiff was also categorized as negative (<-15mL/min/1.73m2), midrange (-15 to 15mL/min/1.73m2), or positive (≥15mL/min/1.73m2).

OUTCOME

Incident AF.

ANALYTICAL APPROACH

Subdistribution hazard models were fit, treating death that occurred before development of AF as a competing event.

RESULTS

During the median follow-up period of 11.7 years, incident AF occurred in 18,994 (5.2%) participants. In the multivariable-adjusted model, participants with a negative eGFRdiff had a higher risk of incident AF (subdistribution HR [SHR], 1.25 [95% CI, 1.20-1.30]), whereas participants with a positive eGFRdiff had a lower risk of AF (SHR, 0.81 [95% CI, 0.77-0.87]) compared with those with a midrange eGFRdiff. When eGFRdiff was treated as a continuous variable in the adjusted model, every 10mL/min/1.73m2 higher eGFRdiff was associated with a 0.90-fold decrease in the risk of incident AF.

LIMITATIONS

A single measurement of baseline serum creatinine and cystatin C levels.

CONCLUSIONS

The difference between cystatin C- and creatinine-based eGFRs was associated with the risk of AF development. A higher eGFRdiff was associated with a lower risk of AF. These findings may have implications for the management of patients at risk of incident AF.

PLAIN-LANGUAGE SUMMARY

The difference between cystatin C-based estimated glomerular filtration rate (eGFR) and creatinine-based eGFR has recently gained attention as a potential indicator of cardiovascular outcomes influenced by factors other than kidney function. This study investigated the association between the differences in 2 eGFRs (cystatin C-based eGFR minus creatinine-based eGFR) and incident atrial fibrillation (AF) among>340,000 participants from the UK Biobank Study. Compared with those with a near zero eGFR difference, participants with a negative eGFR difference had a higher risk of AF, while those with a positive eGFR difference had a lower risk. These findings suggest that measuring eGFR differences may help identify individuals at a higher risk of developing AF.

Correlations between serum kidney injury molecule-1, cystatin C and immunosuppressants: A cross-sectional study of renal transplant patients in Bahrain

Renal transplant patients receive several immunosuppressive drug regimens that are potentially nephrotoxic for treatment. Serum creatinine is the standard for monitoring kidney function; however, cystatin C (Cys C) and kidney injury molecule-1 (KIM-1) have been found to indicate kidney injury earlier than serum creatinine and provide a better reflection of kidney function. Here, we assessed Cys C and KIM-1 serum levels in renal transplant patients receiving mycophenolate mofetil, tacrolimus, sirolimus, everolimus, or cyclosporine to evaluate kidney function. We used both the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2021 equation, which is based on creatinine and combined creatinine with Cys C, and the CKD-EPI 2012 equation, which is based on Cys C alone, to estimate glomerular filtration rate (GFR). Then, we assessed the association between serum KIM-1 and GFR < 90 mL per minute per 1.73 m 2. We observed significantly higher serum Cys C levels in patients with the elevated serum creatinine, compared with those with normal serum creatinine. The estimated GFRs based on creatinine were significantly higher than those based on the other equations, while a significant positive correlation was observed among all equations. Serum KIM-1 levels were negatively correlated with the estimated GFRs by the CKD-EPI Cys C and the combined creatinine with Cys C equations. A serum KIM-1 level above 0.71 ng/mL is likely to indicate GFR < 90 mL per minute per 1.73 m 2. We observed a significant correlation between serum creatinine and Cys C in our renal transplant patients. Therefore, serum KIM-1 may be used to monitor renal function when using potentially nephrotoxic drugs in renal transplants.

Discordances Between Creatinine- and Cystatin C-Based Estimated GFR and Adverse Clinical Outcomes in Routine Clinical Practice

RATIONALE & OBJECTIVE

Cystatin C is recommended for measuring estimated glomerular filtration rate (eGFR) when estimates based on creatinine (eGFRcr) are not thought to be accurate enough for clinical decision making. While global adoption is slow, routine cystatin C testing in Sweden has been available for over a decade, providing real-world evidence about the magnitude of differences between eGFRcys and eGFRcr and their association with clinical outcomes.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

158,601 adults (48% women; mean age 62 years, eGFRcr 80, and eGFRcys 73mL/min/1.73/m2) undergoing testing for creatinine and cystatin C on the same day in connection with a health care encounter during 2010-2018 in Stockholm, Sweden.

EXPOSURE

Percentage difference of eGFRcys minus eGFRcr (eGFRdiff).

OUTCOME

Kidney failure with replacement therapy (KFRT), acute kidney injury (AKI), atherosclerotic cardiovascular disease (ASCVD), heart failure, and death.

ANALYTICAL APPROACH

Multivariable Cox proportional hazards regression.

RESULTS

Discordances between eGFRcr and eGFRcys were common, with eGFRcys being lower than eGFRcr (negative eGFRdiff) in most cases (65%). Patients with larger negative eGFRdiff were older, more often female, with higher eGFRcr and albuminuria, and more comorbid conditions. Compared with patients with similar eGFRcys and eGFRcr, the lowest quartile (eGFRcys > 27% lower than eGFRcr) had the higher HR of all study outcomes: AKI, 2.6 (95% CI, 2.4-2.9); KFRT, 1.4 (95% CI, 1.2-1.6); ASCVD, 1.4 (95% CI, 1.3-1.5); heart failure, 2.0 (95% CI, 1.9-2.2); and all-cause death, 2.6 (95% CI, 2.5-2.7). Conversely, patients in the highest quartile (positive eGFRdiff) were at lower risk.

LIMITATIONS

Observational study, lack of information on indications for cystatin C testing.

CONCLUSIONS

Cystatin C testing in routine care shows that many patients have a lower eGFRcys than eGFRcr, and these patients have a higher risk of multiple adverse outcomes.

PLAIN-LANGUAGE SUMMARY

Clinicians require guidance when there are discrepancies between the estimated glomerular filtration rate based on creatinine (eGFRcr) and based on cystatin C (eGFRcys) in the same individual. Routine cystatin C testing in Sweden for over a decade permits exploration of how common and large these discrepancies are, and their associations with adverse clinical outcomes. In this observational study, we found that discordances between eGFRcys and eGFRcr are common, and 1 in 4 patients tested had an eGFRcys > 28% lower than their eGFRcr. We also show that an eGFRcys that is lower than the eGFRcr consistently identifies patients at higher risk of adverse outcomes, including cardiovascular events, kidney replacement therapy, acute kidney injury, and death.

Discordance Between Creatinine-Based and Cystatin C-Based Estimated GFR: Interpretation According to Performance Compared to Measured GFR

Rationale & Objective

Use of cystatin C in addition to creatinine to estimate glomerular filtration rate (estimated glomerular filtration rate based on cystatin C [eGFRcys] and estimated glomerular filtration rate based on creatinine [eGFRcr], respectively) is increasing. When eGFRcr and eGFRcys are discordant, it is not known which is more accurate, leading to uncertainty in clinical decision making.

Study Design

Cross-sectional analysis.

Setting & Participants

Four thousand fifty participants with measured glomerular filtration rate (mGFR) from 12 studies in North America and Europe.

Exposures

Serum creatinine and serum cystatin C.

Outcomes

Performance of creatinine-based and cystatin C-based glomerular filtration rate estimating equations compared to mGFR.

Analytical Approach

We evaluated the accuracy of eGFRcr, eGFRcys, and the combination (eGFRcr-cys) compared to mGFR according to the magnitude of the difference between eGFRcr and eGFRcys (eGFRdiff). We used CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations to estimate glomerular filtration rate. eGFRdiff was defined as eGFRcys minus eGFRcr and categorized as less than -15, -15 to <15, and ≥15 mL/min/1.73 m2 (negative, concordant, and positive groups, respectively). We compared bias (median of mGFR minus eGFR) and the percentage of eGFR within 30% of mGFR.

Results

Thirty percent of participants had discordant eGFRdiff (21.0% and 9.6% negative and positive eGFRdiffs, respectively). In the concordant eGFRdiff group, all equations displayed similar accuracy. In the negative eGFRdiff groups, eGFRcr had a large overestimation of mGFR (-13.4 [-14.5 to -12.2] mL/min/1.73 m2) and eGFRcys had a large underestimation (9.9 [9.1-11.2] mL/min/1.73m2), with opposite results in the positive eGFRdiff group. In both negative and positive eGFRdiff groups, eGFRcr-cys was more accurate than either eGFRcr or eGFRcys. These results were largely consistent across age, sex, race, and body mass index.

Limitations

Few participants with major comorbid conditions.

Conclusions

Discordant eGFRcr and eGFRcys are common. eGFR using the combination of creatinine and cystatin C provides the most accurate estimates among persons with discordant eGFRcr or eGFRcys.

Endogenous markers of kidney function and renal drug clearance processes of filtration, secretion, and reabsorption

The kidneys are responsible for maintaining physiologic homeostasis. The kidneys clear a variety of drugs and other substances through passive (filtration) and active processes that utilize transport proteins. Renal clearance is comprised of the processes of glomerular filtration, tubular secretion, and tubular reabsorption. Endogenous biomarkers, such as creatinine and cystatin C, are routinely used to estimate renal clearance. Understanding the contributing components of renal function and clearance, through the use of biomarkers, is necessary in elucidating the renal pharmacology of drugs and other substances. While exogenous markers of kidney function have been known for decades, several complexities have limited their usage. Several endogenous markers are being evaluated and hold promise to elucidate the individual components of kidney function that represent filtration, secretion, and reabsorption.

The role of urinary N-acetyl-β-D-glucosaminidase in early detection of acute kidney injury among pediatric patients with neoplastic disorders in a retrospective study

Background

The 1-year cumulative incidence of AKI reportedly is high (52%) in pediatric neoplastic disorders. About half of these events occur within 2 weeks. However, subclinical AKI episodes may remain unrecognized by the conventional creatinine-based approaches. We investigated the diagnostic value of urinary N-acetyl-β-D-glucosaminidase (uNAG) as an early marker of acute kidney injury (AKI).

Methods

In our retrospective study, 33 children with neoplastic disorders were inculded who had serial uNAG tests (at least 5 samples/patient) with a total of 367 uNAG measurements. Renal function was determined by cystatin-C and creatinine based GFR, and relative increase of uNAG index (uNAG_RI). We focused on detecting both clinical and subclinical AKI episodes (according to Biomarker-Guided Risk Assessment using pRIFLE criteria and /or elevated uNAG levels) and the incidence of chronic kidney damage.

Results

Sixty episodes in 26 patients, with positivity at least in one parameter of kidney panel, were identified during the observation period. We detected 18/60 clinical and 12/60 subclinical renal episodes. In 27/60 episodes only uNAG values was elevated with no therapeutic consequence at presentation. Two patients were detected with decreased initial creatinine levels with 3 „silent” AKI.

In 13 patients, modest elevation of uNAG persisted suggesting mild, reversible tubular damage, while chronic tubuloglomerular injury occurred in 5 patients.

Based on ROC analysis for the occurence of AKI, uNAGRI significantly indicated the presence of AKI, the sensitivity and specificity are higher than the changes of GFR_Creat. Serial uNAG measurements are recommended for  the reduction of the great amount of false positive uNAG results, often due to overhydratation.

Conclusion

Use of Biomarker-guided Risk Assessment for AKI identified 1.5 × more clinical and subclinical AKI episodes than with creatinine alone in our pediatric cancer patients. Based on the ROC curve for the occurence of AKI, uNAG_RI has relatively high sensitivity and specificity comparable to changes of GFR_CysC. The advantage of serial uNAG measurements is to decrease the number of false positive results.

Trial registration

The consent to participate is not applicable because it was not reqired for ethical approval and it is a retrospectiv study.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03416-w.

Comparison of Creatinine and Cystatin C to Estimate Renal Function in Geriatric and Frail Patients

The aim of this study was to compare estimated glomerular filtration rate (eGFR) with creatinine (eGFRcrea) and cystatin C (eGFRcys) in geriatric and frail patients. A retrospective, cross-sectional study was performed at a geriatric clinic in Stockholm (n = 95). The revised Lund−Malmö equation was used to calculate eGFRcrea and the Caucasian-Asian-Pediatric-Adult (CAPA) equation was used for eGFRcys. The absolute mean percentage difference between eGFRcrea and eGFRcys was used as a surrogate measure for accuracy in eGFR. Other outcome measures were consistency expressed in Lin’s concordance correlation coefficient and the proportion of consistent staging of renal failure. Subgroup analyses were performed with regard to frailty (according to Clinical Frailty Scale) and age. eGFRcys estimated lower GFR than eGFRcrea across the entire study population as well as in all subgroups (p < 0.05). Difference between the estimates increased with increasing frailty (r2 = 0.15, p < 0.01), but was not significantly affected by age (r2 = 0.004, p = 0.55). In conclusion, eGFRcys was significantly lower compared to eGFRcrea in geriatric and frail patients. Moreover, frailty had greater impact than age on the accuracy of eGFR. However, this study cannot determine if any of the estimates are preferable over the other in this patient group.