Beyond creatinine: New methods to measure renal function?

Accurate assessment of kidney function is essential for diagnosing and managing chronic kidney disease (CKD) and acute kidney injury (AKI), adjusting drug dosages, and predicting clinical outcomes. Despite its ubiquitous use, serum creatinine has significant limitations, necessitating the exploration of alternative and complementary biomarkers and technologies. This review revisits the benefits and limitations of serum creatinine, explores other kidney function biomarkers such as Cystatin C and ProEnkephalin, and examines traditional gold-standard techniques, including creatinine clearance, radioisotopes, and inulin clearance. Furthermore, it highlights innovations in real-time glomerular filtration rate (GFR) measurement, such as transdermal monitoring using MB-102 and dual fluorescent tracers. We conclude with a discussion on the development, validation, and clinical integration of these advancements, which may redefine renal function assessment in the years to come.

Urinary dickkopf-3 as a predictor for postoperative acute kidney injury in the intensive care unit

BACKGROUND

As a life-threatening complication in patients undergoing surgery, acute kidney injury (AKI) is strongly associated with a worse prognosis. Urinary dickkopf-related protein 3 (DKK3) has been identified as a biomarker for predicting postoperative AKI in patients undergoing cardiac surgery.

OBJECTIVE

To investigate the predictive value of urinary DKK3 on postoperative AKI and develop a clinical model based on the predictor for predicting the development of AKI within seven days for patients undergoing noncardiac surgery.

METHODS

All patients who were admitted to the Intensive Care Unit (ICU) after noncardiac surgery from March 2023 to June 2023 were included in this study. The patients' baseline data on demographic characteristics, lifestyle risk factors, medical history, clinical features, and laboratory tests before surgery were collected at the time of admission. Besides, the blood samples for cystatin C and routine laboratory tests and the urine samples for DKK3 tests were simultaneously collected at the time of admission to the ICU. In addition, the independent predictors of postoperative AKI were identified by univariate, multivariate, and LASSO analyses. Moreover, a nomogram for predicting postoperative AKI was developed based on these independent predictors. Finally, the nomogram was evaluated through calibration and decision curve analyses.

RESULTS

A total of 166 patients with a median age of 67 years old were included in this study, including 94 (56.63 %) males. Among these patients, 47 patients (28.3 %) developed postoperative AKI. Additionally, 7 independent risk factors, including preoperative serum creatinine, preoperative eGFR, preoperative serum albumin, preoperative serum potassium ion, cystatin C, uDKK3/uCr, and SOFA score, were selected by univariate and multivariate regression analyses. Eventually, 4 independent risk factors (including preoperative eGFR, cystatin C, uDKK3/uCr, and SOFA score) identified in this study by LASSO analyses were used to establish the nomogram. The area under the receiver operating characteristic (ROC) curve (AUC) for the prediction model was 0.868. The calibration curve and decision curve analysis results demonstrated that the nomogram had good prediction performance.

CONCLUSIONS

Urinary DKK3/creatinine was independently associated with postoperative AKI for patients in the ICU after noncardiac surgery. The nomogram constructed based on uDKK3/uCr, preoperative eGFR, cystatin C, and SOFA score showed a higher accuracy in predicting postoperative AKI.

Increased Serum Cystatin C Levels Were Associated with Depressive Symptoms in Patients with Type 2 Diabetes

BACKGROUND

Existing studies have reported that patients with diabetes mellitus (DM) have an increased risk of depressive symptoms. We aimed to evaluate the association between serum cystatin C levels and depressive symptoms in DM patients.

METHODS

Serum levels of cystatin C were measured in 254 patients with DM at baseline. Cox proportional hazard analysis was used to evaluate the value of serum cystatin C in predicting depressive symptoms in patients with DM.

RESULTS

Multivariate linear regression analysis showed that serum cystatin C levels were independently associated with Centre for Epidemiological Studies Depression (CES-D) scores after adjusting for age, sex, body mass index (BMI), current smoking status, current drinking, admission systolic and diastolic blood pressure (BP), cardiovascular disease (CVD) history and laboratory measurements in patients with DM at baseline (Sβ= -0.127; 95% CI, - 0.185- - 0.083; P=0.002). The multivariate Cox proportional hazard analysis revealed that serum cystatin C (HR=2.360, 95% CI 1.500-3.891, P-trend <0.001) was an independent prognostic factor for cognitive decline in these patients with DM during the follow-up period.

CONCLUSION

Our results showed that increased serum cystatin C levels were significantly and independently associated with depressive symptoms and had independent predictive value for depressive symptoms in patients with DM. Serum cystatin C might enable early recognition of depressive symptoms among DM patients.

The Diagnostic Value of Cystatin C and Mild Hypothermia Therapy Based on Immunoturbidimetry Enhanced by Nanospheres in Asphyxia Neonate

In order to evaluate the early diagnosis value of CysC and the influence of mild hypothermia on the renal damage of asphyxia neonates, the serum cystatin C (CysC) levels of asphyxia neonates and normal neonates were measured by the nanomicrosphere-enhanced immunoturbidimetric method. The treatment was carried out, and the influence of mild hypothermia treatment on the renal damage of asphyxia neonates was analyzed. The results showed that the indicators of the asphyxia group were significantly higher than those of the control group, and the severe asphyxia group was significantly higher than that of the mild asphyxia group, which was statistically significant $\left(p<0.05\right)$ ; the heart rate of patients in the mild hypothermia treatment group decreased gradually with the decrease in body temperature. And compared with the control group, there was a significant difference ( $p<0.05$ ); after symptomatic treatment, the two groups of ALT, AST, BUN, and SCR were improved to varying degrees, and the difference was statistically significant compared with before treatment ( $p<0.05$ ). Studies have shown that serum CysC level can be used as an indicator to detect glomerular filtration function and early asphyxia newborns, and it is sensitive and specific for early diagnosis of kidney damage. At the same time, it can be used to monitor clinical renal function and determine the status of asphyxia newborns.

Characterization of a Murine Model of Oxazolone-Induced Orbital Inflammation

Purpose

Acute orbital inflammation can lead to irreversible vision loss in serious cases. Treatment thus far has been limited to systemic steroids or surgical decompression of the orbit. An animal model that mimics the characteristic features of acute orbital inflammation as found in thyroid eye disease can be used to explore novel treatment modalities.

Methods

We developed a murine model of orbital inflammation by injecting oxazolone into the mouse orbit. The mice underwent magnetic resonance imaging (MRI) and were euthanized at various time points for histologic examination. Immunofluorescence studies of specific inflammatory cells and cytokine arrays were performed.

Results

We found clinical and radiographic congruity between the murine model and human disease. After 72 hours, sensitized mice exhibited periorbital dermatitis and inflammation in the eyelids of the injected side. By one week, increased proptosis in the injected eye with significant eyelid edema was appreciated. By four weeks, inflammation and proptosis were decreased. At all three time points, the mice demonstrated exophthalmos and periorbital edema. Histopathologically, populations of inflammatory cells including T cells, macrophages, and neutrophils shared similarities with patient samples in thyroid eye disease. Proteomic changes in the levels of inflammatory and angiogenic markers correlated to the expected angiogenic, inflammatory, and fibrotic responses observed in patients with thyroid eye disease.

Conclusions

A murine model of orbital inflammation created using oxazolone recapitulates some of the clinical features of thyroid eye disease and potentially other nonspecific orbital inflammation, typified by inflammatory cell infiltration, orbital tissue expansion and remodeling, and subsequent fibrosis.

Translational Relevance

This animal model could serve as a viable platform with which to understand the underlying mechanisms of acute orbital inflammation and to investigate potential new, targeted treatments.

Combining Serum Cystatin C and Urinary N-Acetyl-Beta-D-Glucosaminidase Improves the Precision for Acute Kidney Injury Diagnosis after Resection of Intracranial Space-Occupying Lesions

BACKGROUND

Postoperative acute kidney injury (AKI) is frequent and associated with adverse outcomes. Unfortunately, the early diagnosis of AKI remains a challenge. Combining functional and tubular damage biomarkers may provide better precision for AKI detection. However, the diagnostic accuracy of this combination for AKI after neurosurgery is unclear. Serum cystatin C (sCysC) and urinary albumin/creatinine ratio (uACR) are considered functional biomarkers, while urinary N-acetyl-β-D-glucosaminidase (uNAG) represents tubular damage. We aimed to assess the performances of these clinical available biomarkers and their combinations for AKI prediction after resection of intracranial space-occupying lesions.

METHODS

A prospective study was conducted, enrolling adults undergoing resection of intracranial space-occupying lesions and admitted to the neurosurgical intensive care unit. The discriminative abilities of postoperative sCysC, uNAG, uACR, and their combinations in predicting AKI were compared using the area under the receiver operating characteristic curve (AUC-ROC), continuous net reclassification index (cNRI), and incremental discrimination improvement (IDI).

RESULTS

Of 605 enrolled patients, AKI occurred in 67 patients. The cutoff values of sCysC, uNAG, and uACR to predict postoperative AKI were 0.72 mg/L, 19.98 U/g creatinine, and 44.21 mg/g creatinine, respectively. For predicting AKI, the composite of sCysC and uNAG (AUC-ROC = 0.785) outperformed either individual biomarkers or the other two panels (uNAG plus uACR or sCysC plus uACR). Adding this panel to the predictive model improved the AUC-ROC to 0.808. Moreover, this combination significantly improved risk reclassification over the clinical model alone, with cNRI (0.633) and IDI (0.076). Superior performance of this panel was further confirmed with bootstrap internal validation.

CONCLUSIONS

Combination of functional and tubular damage biomarkers improves the predictive accuracy for AKI after resection of intracranial space-occupying lesions.

Renal function and delirium in older fracture patients: different information from different formulas?

OBJECTIVES

the association between renal function and delirium has not been investigated in older fracture patients. Creatinine is frequently low in these subjects, which may influence the association between delirium and renal function as estimated with creatinine-based formulas. Cystatin C could be a more reliable filtration marker in these patients.

AIM

to confirm the association between renal function and delirium in older fracture patients comparing creatinine- and cystatin-based estimated glomerular filtration rate (eGFR) METHODS: patients aged 65+ requiring surgery for traumatic bone fractures were included. Six equations were used to calculate eGFR, based on serum creatinine and/or cystatin C obtained within 24 h of admission: Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology (CKD-EPIcr, CKD-EPIcys, CKD-EPIcr-cys) and Berlin Initiative Study equations (BIS-1, BIS-2). Delirium was identified with a chart-based method.

RESULTS

571 patients (mean age 83) were enrolled. Delirium occurred in the 34% and was associated with a lower eGFR regardless of the equation used. In a multivariable model, the association between moderate renal impairment (eGFR 30-60 ml/min/1.73 m2) and delirium remained significant in patients aged 75-84 and only when estimated with cystatin-based or BIS-1 equations. Only dementia was significantly associated with delirium in subjects 85+.

CONCLUSIONS

in older fracture patients, moderate renal impairment was independently associated with delirium only among subjects aged 75-84, when eGFR was estimated with cystatin-based or BIS 1 equations, and not with the most commonly used equations (MDRD, CKD-EPIcr).

The influence of glycemic status on the performance of cystatin C for acute kidney injury detection in the critically ill

OBJECTIVE

Serum cystatin C (sCysC) used clinically for detecting early acute kidney injury (AKI) was reported to be independently associated with hemoglobin (HbA1c) levels, diabetes, and prediabetes. We aimed to assess the influence of HbA1c levels, diabetes, or prediabetes on the performance of sCysC for AKI detection in critically ill adults.

METHODS

A prospective observational study was conducted in a mixed medical-surgical intensive care unit (ICU). Patients were divided into four quartiles based on levels of HbA1c or serum glucose at ICU admission, respectively. Additionally, patients were stratified into four subgroups according to HbA1c levels and history of diabetes, namely recognized diabetes (previous diagnosis of diabetes), unrecognized diabetes, prediabetes, and normal glycemic status. Comparisons were made using the area under the receiver operator characteristic curve (AUC) for AKI detection, and reassessed after patient stratification by above-mentioned glycemic status.

RESULTS

Multivariable linear regression revealed that HbA1c levels and history of diabetes were positively related with sCysC (all p < .05). Although stratification for above-mentioned glycemic status displayed no significant difference between AUC of sCysC (all p > .05), sCysC yielded the highest AUCs for detecting AKI in diabetic patients. Moreover, higher optimal cutoff values of sCysC to detect AKI were observed in patients with versus without diabetes.

CONCLUSION

Glycemic status has no significant impact on the accuracy of sCysC for AKI detection in critically ill adults and a higher optimal cutoff value of sCysC for AKI detection should be considered in diabetic patients.

Plasma cystatin C as a marker for estimated glomerular filtration rate assessment in HIV-1-infected patients treated with dolutegravir-based ART

Objectives

Inhibition of the organic cation transporter-2 renal tubule transporter by dolutegravir leads to serum creatinine increase. Serum cystatin C is a non-organic cation transporter-2-dependent marker, possibly enabling glomerular filtration rate (GFR) estimation under dolutegravir. Our goal was to evaluate the changes in creatinine- and cystatin C-based estimated GFR values before and after dolutegravir initiation.

Methods

Creatinine and cystatin measurements were carried out on frozen plasma samples from HIV-1-infected patients, before and after dolutegravir initiation, between October 2016 and March 2017 at Pitié-Salpêtrière Hospital. CKD-EPI equations were used to estimate mean GFR from creatinine and cystatin C values. Variations were analysed by paired t-test.

Results

Forty-four patients were included [median age = 48 years (IQR 36-58) and median CD4 count = 592 cells/mm3 (IQR 388-728)], including 6 ART-naive patients and 38 on switch strategies [72% with viral load <50 copies/mL and median ART duration = 13 years (IQR 5-20)]. Before dolutegravir initiation (median time = 41 days), 19 patients (43%) had creatinine-based estimated GFR <90 mL/min/1.73 m2 and 11 (25%) had cystatin C-based estimated GFR <90 mL/min/1.73 m2. After dolutegravir initiation, serum creatinine values significantly increased (+8.6 μmol/L, 95% CI +5.8; +11.4, P < 0.001) and associated estimated GFR significantly decreased (-7.7 mL/min/1.73 m2, 95% CI -10.4; -5.1, P < 0.001). In contrast, there was no significant change in cystatin C value variation and associated estimated GFR. The same results were observed regardless of renal function at baseline.

Conclusions

Creatinine values increased after dolutegravir initiation, whereas no change was observed for cystatin C values. Use of cystatin C may enable better understanding of plasma creatinine fluctuations after dolutegravir initiation, particularly in high-risk renal patients.

Decreased Renal Function Induced by High-Fat Diet in Wistar Rat: The Role of Plasma Angiotensin Converting Enzyme 2 (ACE2)

Researches on the effects of High Fat Diet (HFD) on decreased renal function with cystatin C (cysC) serum levels biomarker are few and show different findings. Renin Angiotensin System (RAS) plays a key role in controlling renal function and one of the integral components of the RAS is Angiotensin Converting Enzyme 2 (ACE2). Research on the relationship between plasma ACE2 levels with serum cysC levels in animals induced by HFD has not been done. We hypothesize that administration of HFD can cause a decline in early stage renal function through the role of ACE2. 30 male wistar rats aged 10-12 weeks (body weight between 170-220 grams) were randomly divided into 5 groups (6 rats/group): baseline, normal diet for 8 weeks (ND8), ND for 16 weeks (ND16), HFD for 8 weeks (HFD8) and HFD for 16 weeks (HFD16). Body weight and naso-anal length were measured to get the index value of obesity and body fat percentage. Obesity index measured are lee index, rohrer index and TM index. Blood samples obtained by intracardiac for examination of plasma ACE2 levels and serum cysC levels. After 8 and 16 weeks, HFD increases body weight, obesity index and body fat percentage. HFD also increases plasma ACE2 levels and serum cysC levels. Body weight, obesity index and body fat percentage have a positive correlation with plasma ACE2 levels. Plasma ACE2 levels were positively correlated with serum cysC levels. HFD causes a decrease of early stage renal function as evidenced by the increase in serum cysC levels. Plasma ACE2 levels play a role in the pathogenesis of the decline in early stage renal function induced by HFD.

Impact of thyroid function on cystatin C in detecting acute kidney injury: a prospective, observational study

BACKGROUND

Cystatin C (Cys C) used clinically for detecting early acute kidney injury (AKI) was reported to be associated with thyroid function. Therefore, whether the performance of Cys C is affected by thyroid hormones has raised concern in critically ill patients. This study aimed to investigate the impact of thyroid hormones on the diagnostic and predictive accuracy of Cys C for AKI, and hence optimize the clinical application of Cys C.

METHODS

A prospective observational study was conducted in the general intensive care units (ICUs). Serum creatinine (SCr), Cys C, and thyroid function were documented for all patients at ICU admission. Patients were separated into five quintiles based on free triiodothyronine (FT3) and total triiodothyronine (TT3), and two categories according to the presence of low T3 syndrome or not. The impact of thyroid function on the performance of Cys C in diagnosing and predicting AKI was assessed by area under the receiver operating characteristic curve (AUC).

RESULTS

The AKI incidence was 30.0% (402/1339); 225 patients had AKI upon entry, and 177 patients developed AKI during the subsequent 7 days. The AUCs for Cys C in detecting total AKI, established AKI, and later-onset AKI was 0.753, 0.797, and 0.669, respectively. The multiple linear regression analysis demonstrated that TT3 and FT3 were independently associated with Cys C. Overall, although Cys C did not yield any significant difference in AUCs for detecting AKI among patients with different thyroid hormones, the optimal cut-off value of Cys C to detect AKI was markedly different between patients with and without low T3 syndrome.

CONCLUSIONS

The thyroid function had no significant impact on the diagnostic and predictive accuracy of Cys C in detecting AKI in ICU patients. However, the optimal cut-off value of Cys C to detect AKI could be affected by thyroid function.

Correlation of Thyroid Hormone Profile with Biochemical Markers of Renal Function in Patients with Undialyzed Chronic Kidney Disease

OBJECTIVE

The present study was conducted to evaluate the correlation of renal functions with thyroid hormone levels in patients with undialyzed chronic kidney disease (CKD). Literature shows significant alteration in thyroid hormone function tests in CKD patients who are receiving long-standing dialysis treatment. However, not much is described in those receiving conservative management without dialysis. Although CKD is associated with an increased prevalence of primary hypothyroidism, various studies on thyroid hormone status in uremic patients have reported conflicting results.

METHODOLOGY

Thyroid hormone levels and biochemical markers of renal function were estimated in 30 undialyzed CKD patients and similar number of age- and sex-matched healthy controls, followed by statistical analysis and correlation.

RESULTS

Free triiodothyronine (FT3) and free thyroxine (FT4) were found to be significantly reduced (P < 0.001 for each) in undialyzed CKD patients whereas thyroid-stimulating hormone (TSH) levels showed statistically insignificant alteration in both groups. We also observed that urea and creatinine were negatively correlated whereas creatinine clearance was positively correlated with both FT3 and FT4 having high statistical (two tailed) significance with P < 0.001. Nonsignificant correlation was seen between blood urea and TSH (r = 0.236, P = 0.069), creatinine clearance, and TSH (r = 0.206, P = 0.114 Pearson's correlation coefficient). There is just significant positive correlation between the serum creatinine values and TSH (r = 0.248, P = 0.049).

CONCLUSIONS

Thyroid hormones were significantly decreased in undialyzed CKD patients as compared to healthy controls.

Serum Cystatin C Predicts AKI and the Prognosis of Patients in Coronary Care Unit: a Prospective, Observational Study

BACKGROUND/AIMS

Acute Kidney Injury (AKI) is a serious clinical state associated with high morbidity and mortality, particularly in critical ill patients. We investigated the hypothesis that serum Cystatin C (sCysC) is a good predictor for AKI and may affect the short-term prognosis of coronary care unit (CCU) patients.

METHODS

In this prospective, observational study, we screened 412 adults admitted to the CCU from January 1, 2014 to June 1, 2015 at Zhongnan Hospital of Wuhan University. Serum samples were obtained at the time of admission, and sCysC was quantified through nephelometry. AKI was defined based on KDIGO-AKI criteria. After the patients' hospital discharge, the survivors in this study were followed up for up to 2 years. The primary endpoint was the incidence of AKI stratified by severity stage, while the second endpoints included 2-year mortality, rehospitalization and failure in renal recovery rates, as well as the progression of AKI to CKD.

RESULTS

According to the KDIGO-AKI criteria, AKI occurred in 130 (31.6%) patients. After multivariate adjustments, the highest quartile of sCysC was associated with a 9-fold increased risk of incident AKI compared with the lowest quartile. For predicting AKI, sCysC [area under the receiver operating characteristic curve (AUC=0.842)] outperformed β2-micro globulin (AUC=0.813) and the clinical model (AUC=0.777), and a cutoff of 1.255 mg/L yielded good sensitivity and specificity. After a median 19.8-month follow-up, 112 (27.2%) patients died within 2 years after admission. The sCysC independently predicted the risk of 2-year mortality [adjusted odds ratio (OR), 4.955; 95% confidence interval (95% CI), 2.853 to 8.603] and rehospitalization (OR, 3.128; 95% CI, 2.011 to 4.867), as well as renal recovery failure (OR, 3.618, 95% CI, 1.753 to 7.463).

CONCLUSIONS

Serum CysC is a strong predictor of AKI and the short-term prognosis of CCU patients.