Serum Cystatin C, a Sensitive Marker of Renal Function and Cardiovascular Disease, Decreases After Smoking Cessation

Discrepancy between estimated glomerular filtration rate by creatinine versus cystatin C in different patient care settings

OBJECTIVE

Estimated glomerular filtration rate (eGFR) calculated by cystatin C (cysC) has been recommended for broader adoption. This study assessed the discrepancy between eGFR calculated by cysC (eGFRcys) and creatinine (eGFRcr) in different patient care settings and explored potential contributing factors to such discrepancies.

METHODS

This retrospective study included 2072 patients with paired cystatin C and creatinine results in different patient care settings. Delta eGFRcr-cys (eGFRcr - eGFRcys) was analyzed in relationship to patient care settings and the Elixhauser Comorbidity index. The 90-day survival in patients with different delta eGFR was assessed by Kaplan-Meier analysis, univariate and multivariate Cox proportional hazard models. In addition, discrepancy between eGFRcys and eGFRcr was analyzed in 50 ambulatory patients with systemic inflammation but normal kidney function.

RESULTS

Inpatients had higher cysC (median 1.91 mg/L), lower eGFRcys (median 31 mL/min/1.73 m2), and larger delta eGFRcr-cys (median 18 mL/min/1.73 m2) than outpatients (cysC median 1.53 mg/L, p < 0.0001, eGFRcys median 41 mL/min/1.73 m2, p < 0.0001, delta eGFRcr-cys median 4 mL/min/1.73 m2, p < 0.0001). Higher Elixhauser Comorbidity index correlated with lower eGFRcys and larger delta eGFRcr-cys, with median delta eGFRcr-cys 11 and 6 mL/min/1.73 m2 in patients with a Comorbidity index > 15 and ≤ 15, respectively (p < 0.0001). Increased delta eGFRcr-cys was associated with worse 90-day survival. Patients with systemic inflammation but normal kidney function had lower eGFRcys (median 77.5 mL/min/1.73 m2) than eGFRcr (median 97 mL/min/1.73 m2, p < 0.001), with red blood cell abnormalities as associated factors.

CONCLUSION

Inflammation and comorbidities are associated with decreased eGFRcys and large discrepancies between eGFRcr and eGFRcys independent of kidney function and are most apparent in inpatients. Creatinine-cysC combined eGFR reduces this discrepancy and should be broadly adopted.

Trends in renal function in Northern Sweden 1986-2014: data from the seven cross-sectional surveys within the Northern Sweden MONICA study

OBJECTIVE

The prevalence of chronic kidney disease (CKD) is increasing globally, and CKD is closely related to cardiovascular disease (CVD). CKD and CVD share several risk factors (RF), such as diabetes, hypertension, obesity and smoking, and the prevalence of these RF has changed during the last decades, and we aimed to study the effect on renal function over time.

DESIGN

Repeated cross-sectional population-based studies.

SETTING

The two Northern counties (Norr- and Västerbotten) in Sweden.

PARTICIPANTS

Within the MONitoring Trends and Determinants of CArdiovascular Disease (MONICA) study, seven surveys were performed between 1986 and 2014, including participants aged 25-64 years (n=10 185).

INTERVENTIONS

None.

MEASURES

Information on anthropometry, blood pressure and cardiovascular risk factors was collected. Creatinine and cystatin C were analysed in stored blood samples and the estimated glomerular filtration rate (eGFR) calculated using the creatinine-based Lund-Malmö revised and Chronic Kidney Disease Epidemiology Collaboration (eGFRcrea) equations as well as the cystatin C-based Caucasian, Asian, Paediatric and Adult cohort (CAPA) equation (eGFRcysC). Renal function over time was analysed using univariable and multivariable linear regression models.

RESULTS

Renal function, both eGFRcrea and eGFRcysC, decreased over time (both p<0.001) and differed between counties and sexes. In a multivariable analysis, study year remained inversely associated with both eGFRcrea and eGFRcysC (both p<0.001) after adjustment for classical cardiovascular RF.

CONCLUSION

Renal function has deteriorated in Northern Sweden between 1986 and 2014.

Time to Rethink the Current Paradigm for Assessing Kidney Function in Drug Development and Beyond

Chronic kidney disease (CKD) is an important health issue that affects ~ 9.1% of the world adult population. Serum creatinine is the most commonly used biomarker for assessing kidney function and is utilized in different equations for estimating creatinine clearance or glomerular filtration rate (GFR). The Cockcroft-Gault formula for adults and "original" Schwartz formula for children have been the most commonly used equations for estimating kidney function during the last 3-4 decades. Introduction of standardized serum creatinine bioanalytical methodology has reduced interlaboratory variability but is not intended to be used with Cockcroft-Gault or original Schwartz equations. More accurate equations (for instance, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for adults and bedside Schwartz or Chronic Kidney Disease in Children Schwartz equation for children) based on standardized serum creatinine values (and another biomarker-cystatin C) have been introduced and validated in recent years. Recently, the CKD-EPI equation refitted without a race variable was introduced. Clinical practice guidance in nephrology advocates a shift to these equations for managing health care of patients with CKD. The guidance also recommends use of albuminuria in addition to GFR for CKD diagnosis and management. Significant research with large data sets would be necessary to evaluate whether this paradigm would also be valuable in drug dose adjustments. This article attempts to highlight some important advancements in the field from a clinical pharmacology perspective and is a call to action to industry, regulators, and academia to rethink the current paradigm for assessing kidney function to enable dose recommendation in patients with CKD.

Increased serum cystatin C levels and responses of pancreatic α- and β-cells in type 2 diabetes

BACKGROUND

Increased serum cystatin C (CysC) can predict the onset of type 2 diabetes (T2D). Meanwhile, impaired pancreatic α- and β-cell functions get involved in the pathophysiological processes of T2D. So this study was to explore the relationships between serum CysC levels and pancreatic α- and β-cell functions in T2D.

METHODS

In this cross-sectional observational study, a total of 2634 patients with T2D were consecutively recruited. Each recruited patient received a serum CysC test and oral glucose tolerance test for synchronous detection of serum C-peptide and plasma glucagon. As components of pancreatic β-cell function, insulin secretion and sensitivity indices were evaluated by C-peptide area under the curve (AUC-CP) and C-peptide-substituted Matsuda's index (Matsuda-CP), respectively. Fasting glucagon (F-GLA) and post-challenge glucagon calculated by glucagon area under the curve (AUC-GLA) were used to assess pancreatic α-cell function. These skewed indices and were further natural log-transformed (ln).

RESULTS

With quartiles of serum CysC levels ascending, AUC-CP, F-GLA and AUC-GLA were increased, while Matsuda-CP was decreased (P for trend <0.001). Moreover, serum CysC levels were positively related to lnAUC-CP, lnF-GLA and lnAUC-GLA (r= 0.241, 0.131 and 0.208, respectively, P < 0.001), and inversely related to lnMatsuda-CP (r= -0.195, P < 0.001). Furthermore, after controlling for other relevant variables via multivariable linear regression analysis, serum CysC levels were identified to account for lnAUC-CP (β= 0.178, t= 10.518, P < 0.001), lnMatsuda-CP (β= -0.137, t= -7.118, P < 0.001), lnF-GLA (β= 0.049, t= 2.263, P = 0.024) and lnAUC-GLA (β= 0.121, t= 5.730, P < 0.001).

CONCLUSIONS

Increased serum CysC levels may be partly responsible for increased insulin secretion from β-cells, decreased systemic insulin sensitivity, and elevated fasting and postprandial glucagon secretion from α-cells in T2D.

Identification and Comparison of Potential Biomarkers by Proteomic Analysis in Traditional Chinese Medicine-Based Heart Failure Syndromes

Heart failure (HF) is an epidemic disease affecting a large population worldwide. Traditional Chinese medicine (TCM) is playing an increasingly important role in the clinical treatment of HF. According to the TCM theory, HF could be classified into Yang deficiency and Qi-yin deficiency; however, there are few objective and biological lines of evidence for differentiation of TCM HF syndromes to date. In this study, data-independent acquisition (DIA) mass spectrometry was applied to comparatively analyze the protein expression in serum samples obtained from 12 Yang deficiency patients, 12 Qi-yin deficiency patients, and 12 healthy volunteers. Compared to the healthy controls, a total of 121 differentially expressed proteins (DEPs) (77 upregulated and 44 downregulated proteins) were identified in Yang deficiency samples, while 59 DEPs (49 upregulated and 10 downregulated proteins) were detected in Qi-yin deficiency samples. Enrichment analyses of these DEPs based on the GO and KEGG databases revealed functional clusters associated with the immune system, signal transduction, and infectious disease. Several previously reported HF biomarker proteins were found to be the hub proteins in a protein-protein interaction network analysis. Three novel hub DEPs were identified as potential biomarkers for differentiation between different TCM syndromes of HF. The results provide biological insight into the differences of different TCM HF syndromes and an opportunity for specific biomarker identification for different TCM HF syndromes.

Utility of a Score for Predicting Glomerular Filtration Rate Overestimation in Patients with Cardiovascular and Renal Diseases and Their Risk Factors

Objective We recently reported a novel score for the detection of glomerular filtration rate (GFR) overestimation using a creatinine-based equation. We examined the utility of this score in patients with cardiovascular/renal diseases and diabetes mellitus. Methods We enrolled 1,425 patients (65±15 years old; 37% women) who were admitted to our hospital for the management of cardiovascular and renal diseases and their risk factors. Overestimation of the GFR (OE) was defined as a creatinine-based GFR (eGFRcre) ≥120% of the cystatin C-based estimated GFR. The OE score was calculated as the sum of the scores for the body weight, hemoglobin concentration, and blood urea nitrogen (BUN)/serum creatinine (Scr), totaling 1 point if the body weight was <63.0 kg in men or <42.0 kg in women, 1 point if the hemoglobin concentration was <12.4 g/dL in men or <11.0 g/dL in women, and 1 point if the BUN/Scr was >26.5. Results The proportion of patients with OE was 14.2%. The score predicted OE with a sensitivity of 70.8% and a specificity of 99.6%, and the sensitivity was increased in patients ≥75 years old (88.3%) and decreased in diabetics (58.6%). When patients were divided into subgroups by the total score, the frequencies of OE were 8% (59/754), 14% (72/502), 38% (58/151), and 72% (13/18) in patients with scores of 0, 1, 2, and 3, respectively. Conclusion The OE score is useful for detecting elderly cases of cardiovascular and renal diseases in which eGFRcre overestimates the GFR, although its utility is limited in diabetics.

Association between socioeconomic position and cystatin C in the Heinz Nixdorf Recall Study

Social inequalities in health and disease are well studied. Less information is available on inequalities in biomarker levels indicating subclinical stages of disease such as cystatin C, an early diagnostic marker of renal dysfunction and predictor for cardiovascular disease. We evaluated the relationship between cystatin C, socioeconomic position (SEP) and established cardiovascular risk factors in a population-based study. In 4475 men and women aged 45–75 years participating in the baseline examination of the Heinz Nixdorf Recall Study cystatin C was measured from serum samples with a nephelometric assay. SEP was assessed by education and household income. Linear regression models were used to analyse the association between SEP and cystatin C as well as the impact of cardiovascular risk factors (i.e., body mass index, blood pressure, blood glucose, diabetes mellitus, blood lipids, C-reactive protein, smoking) on this association. After adjustment for age and sex cystatin C decreased by 0.019 mg/l (95% confidence interval (CI) − 0.030 to − 0.008) per five years of education. While using a categorical education variable cystatin C presented 0.039 mg/l (95% CI 0.017–0.061) higher in men and women in the lowest educational category (≤ 10 years of education) compared to the highest category (≥ 18 years). Concerning income, cystatin C decreased by 0.014 mg/l (95% CI − 0.021 to − 0.006) per 1000 € after adjustment for age and sex. For men and women in the lowest income quartile cystatin C was 0.024 mg/l (95% CI 0.009–0.038) higher compared to the highest income quartile. After adjusting for established cardiovascular risk factors the observed associations were substantially diminished. Social inequalities seem to play a role in subclinical stages of renal dysfunction, which are also related to development of cardiovascular disease. Adjustment for traditional cardiovascular risk factors showed that these risk factors largely explain the association between SEP and cystatin C.