Gender does not influence cystatin C concentrations in healthy volunteers

Embedding Equity and Inclusion Principles Into Nephrology Board Examinations: An Essential Part of Our Path Toward Kidney Health Justice

Recognition of widespread health inequalities across disease conditions and their startling impact on morbidity and health care costs have motivated multiple professional societies to ensure board examinations reflect and enhance inclusive, anti-biased, and equitable care. In this perspective, we offer five nephrology case examples and accompanying learning objectives to demonstrate how principles of inclusion, equity, and anti-bias can be embedded into nephrology examinations to enhance care for all populations.

Sex difference in the association between creatinine-to-cystatin C ratio and metabolic syndrome among Chinese adults

Background

Metabolic syndrome (MetS), characterized by central obesity, insulin resistance, dyslipidemia, and hypertension, affects 20-25% of the global population. The creatinine-to-cystatin C ratio (CCR) is an indicator of skeletal muscle mass. While CCR may play a role in MetS development, sex differences in these associations are not fully understood. Therefore, this study aimed to investigate how CCR levels are associated with MetS in a Chinese adult population, focusing on possible sex disparities.

Method

We conducted a retrospective cross-sectional analysis of 9,376 adults from Xiamen Chang Gung Hospital between 2014 to 2016. We examined the relationship between CCR and MetS, adjusting for cardiometabolic risk factors.

Results

The prevalence of MetS was 24.7% in males and 18.0% in females. Interestingly, we observed significant sex differences in the association between CCR quartiles and MetS. Females in the lowest CCR quartile had a significantly higher risk of MetS (odds ratio=1.84). Receiver operating characteristic curve analysis revealed acceptable diagnostic power of CCR for MetS in females (area under the curve=0.65) but not in males.

Conclusion

Our findings suggest that CCR is an independent risk factor for MetS in females, highlighting the importance of sex-specific assessments when evaluating MetS risk.

Risk factors for diabetic foot ulcers: A systematic review and meta-analysis

OBJECTIVE

To systematically evaluate the risk factors for developing diabetic foot ulcers (DFU).

METHODS

The Cochrane Library, PubMed, Web of Science, SinoMed, CNKI, VIP, and Wanfang Data were searched for relevant studies on DFU risk factors, and the search time frame was from database creation to March 2022. Meta-analysis was performed using RevMan 5.3.

RESULTS

A total of 26 publications were included, including 3 cohort studies, 22 case-control studies, and one cross-sectional study. Meta-analysis showed that advanced age [MD = 6.04, 95% CI (3.92, 8.16)], male [OR = 1.84, 95% CI (1.48, 2.29)], elevated body mass index [MD = 1.58, 95% CI (0.47, 2.69)], prolonged duration of diabetes [MD = 2.72, 95% CI (2.33, 3.11)], comorbid nephropathy [OR = 3.15, 95% CI (2.68, 4.60)], comorbid neuropathy [OR = 4.80, 95% CI (2.79, 8.27)], comorbid retinopathy [OR = 3.37, 95% CI (2.26, 5.02)], elevated systolic blood pressure [OR = 8.19, 95% CI (6.33, 10.05)], elevated fasting glucose [MD = 1.60, 95% CI (0.21, 3.00)], elevated glycated hemoglobin [MD = 1.24, 95% CI (0.94, 1.54)], elevated triglycerides [MD = 0.44 (95% CI (0.15, 0.73)], elevated fibrinogen [MD = 1.35, 95% CI (0.62, 2.08)], elevated white blood cell count [MD = 2.56, 95% CI (2.24, 2.88)], elevated C-reactive protein [MD = 15.08, 95% CI (8.03, 22.13)], decreased ankle-brachial ratio [MD = -0.26, 95% CI (-0.36, -0.16)], and decreased total protein levels [MD = -4.58, 95% CI (-6.91, -2.25)] were risk factors for developing DFU (p < 0.05), and increased HDL cholesterol levels [MD = -0.22, 95% CI (-0.36, -0.08)] were protective factor for developing DFU (p < 0.05).

CONCLUSION

There are many risk factors for developing of ulcers in the diabetic feet, and early prevention and intervention should be performed as early as possible to assess the risk of developing diabetic foot patients.

Estimating eGFR using serum creatinine or cystatin C in healthy Vietnamese population

Very few studies worldwide have assessed the estimated glomerular filtration rate (eGFR) using serum cystatin C (ScysC) in comparison to the gold standard measured glomerular filtration rate (mGFR) with a gamma camera technique using 99m-Technetium-Diethylene Triaminepentoacetic Acid (99mTc-DTPA). To determine the eGFR formula with the most accurate estimate of glomerular filtration rate when compared with mGFR in a healthy population in Vietnam. We conducted a cross-sectional descriptive study of more than 100 adults without hypertension. The study subjects were examined for general characteristics and blood biochemistry tests to assess eGFR, and the glomerular filtration rate was measured using 99mTc-DTPA with the Gates technique to record mGFR. The estimated values of the eGFR formula were evaluated and compared with the actual mGFR using 99mTechnetium-DTPA. Serum creatinine (Scr) concentration showed a significant difference between males and females: 0.9 ± 0.1 versus 0.8 ± 0.1 (P < .001), while ScysC concentration did not show this difference. The mGFR in the age groups < 40, 40 to 59, and ≥ 60: 105.0 ± 9.9, 94.8 ± 8.6, and 93.4 ± 10.6, respectively (P < .001). The eGFR-CKD-EPI-cystatin C 2012 formula showed the highest positive correlation with mGFR (ΔGFR = -1.6, R = 0.68, P < .001). eGFR calculated using cystatin C does not require sex adjustment, whereas, for creatinine, sex adjustment is necessary. The eGFR-CKD-Epi-CysC formula showed the lowest difference and a strong correlation with mGFR.

Age-adjusted reference values and influencing factors of cystatin C in healthy Chinese population

BACKGROUND

Normative distribution of serum cystatin C and relationship with sex and age in healthy adult Chinese population is unknown.

METHODS

This is a prospective cohort study. Adult subjects (18 years of age and older) who underwent annual health examination at the Health Management Center in Sir Run Run Hospital were eligible. Subjects with major diseases, e.g., hypertension, diabetes, chronic kidney disease, obesity (body mass index ≥ 28 kg/m²) were excluded from the analysis. Multivariate logistic regression analysis was conducted to identify risk factors of elevated cystatin C (> 1.03 mg/L). Data are shown as median and 95% confidence interval (CI).

RESULTS

The final analysis included a total of 10,640 subjects (40 ± 12 years, 52% men). The median serum cystatin C concentration was 0.73 mg/L (95% CI 0.52-1.03 mg/L) in the overall analysis, 0.79 (95% CI 0.59-1.07 mg/L) in men, and 0.67 (95% CI 0.49-0.95 mg/L) in women. In the multivariate regression analysis, elevated cystatin C was independently associated with the male sex (odds ratio 1.94; 95% CI 1.07-3.52), older age (odds ratio 1.04 every year; 95% CI 1.02-1.06), higher body mass index (odds ratio 1.70; 95% CI 1.01-2.83), uric acid (odds ratio 1.00; 95% CI 1.00-1.01), and β2-microglobulin (odds ratio 39.35; 95% CI 22.90-67.64).

CONCLUSION

The median serum cystatin C concentration was 0.73 (95% CI 0.52-1.03 mg/L) in healthy adult Chinese population, 0.79 (95% CI 0.59-1.07 mg/L) in men, and 0.67 (95% CI 0.49-0.95 mg/L) in women. Elevated cystatin C was associated with the male sex, older age and higher body mass index.

Educational review: measurement of GFR in special populations

IMPORTANCE

Changes in kidney function are typically followed by the sequential estimation of glomerular filtration rate (eGFR). Formulae for eGFR work well on a population basis, but there are well-known conditions where they do not work.

OBJECTIVE

The purpose of this review is to summarize the existing literature on special populations in the pediatric age range and provide recommendations on how to estimate GFR in these populations.

FINDINGS

The reliability of creatinine depends on muscle mass, while cystatin C (not widely available) is limited by inflammation and changes in protein catabolism. Various dietary factors can alter eGFR. Renal function in neonates changes drastically every day, and there are currently no satisfactory reference intervals for routine pediatric use. Gender effects and conditions such as wasting disease and obesity require alternative ways to obtain eGFR. In oncology patients, chemotherapy may negatively affect renal function, and nuclear GFR measurements may be necessary. For body builders, high muscle mass may lead to underestimation of eGFR using creatinine.

CONCLUSIONS AND RELEVANCE

Clinicians should be aware of special populations that may yield misleading eGFRs with conventional creatinine-based formulae, and that the alternative methods may be more appropriate for some populations.

Male sex and vascular risk factors affect cystatin C-derived renal function in older people without diabetes or overt vascular disease

Background/objectives: to explore the effect of ageing on renal function with cystatin C as the marker of glomerular filtration rate (GFR) in the general population without vascular disease or diabetes.

Design: a cross-sectional analysis of a healthy subset from the Good Aging in Skåne-cohort study representative of the Swedish general population.

Subjects: 1252 participants without vascular disease and diabetes (43.9% men) of whom 203 were over 80 years old were included from the original cohort of 2931.

Methods: plasma cystatin C and plasma creatinine were used as markers for GFR. Estimated GFR (eGFR) was calculated with three chronic kidney disease epidemiology collaboration (CKD-EPI) formulas involving cystatin C, creatinine or both.

Results: the median for plasma cystatin C was 0.93 mg/l (60–69 years old), 1.04 (70–79 years old) and 1.24 (80+ years old). The difference in mg/l between the 5th and 95th percentile was 0.46, 0.62 and 0.90 for these age groups. Male sex increased the age effect on plasma cystatin C levels with 0.004 mg/l/year (P = 0.03), adjusted for vascular risk factors. Smoking, lower HDL and higher diastolic blood pressure were associated with higher cystatin C levels. 54.7% (CKD-EPI creatinine) to 73.9% (CKD-EPI cystatin C) of the 80+ had an eGFR < 60 ml/min/1.73 m².

Conclusion: non-diabetics without overt vascular disease exhibit an age related but heterogeneous decline in renal function. The ageing effect is more pronounced in men. At least half of healthy 80+ years old could be expected to have at least CKD Stage 3 with eGFR < 60 ml/min/1.73 m².

Impact of Growth Hormone on Cystatin C

Background

Cystatin C (CysC) is an alternative marker to creatinine for estimation of the glomerular filtration rate (GFR). Hormones such as thyroid hormones and glucocorticoids are known to have an impact on CysC. In this study, we examined the effect of growth hormone (GH) on CysC in patients with acromegaly undergoing transsphenoidal surgery.

Methods

Creatinine, CysC, GH and insulin-like growth factor-1 (IGF-1) were determined in 24 patients with acromegaly before and following transsphenoidal surgery. Estimated GFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration formula.

Results

In all patients, surgical debulking resulted in decreased clinical disease activity and declining GH/IGF-1 levels. Postoperatively, biochemical cure was documented in 20 out of 24 patients. Creatinine levels (mean ± SEM) increased from 72 ± 3 to 80 ± 3 µmol/l (p = 0.0004) and concurrently, estimated GFR decreased from 99 ± 3 to 91 ± 3 ml/min (p = 0.0008). In contrast to creatinine, CysC levels decreased from 0.72 ± 0.02 to 0.68 ± 0.02 mg/l (p = 0.0008).

Conclusions

Our study provides strong evidence for discordant effects of GH on creatinine and CysC in patients with acromegaly undergoing transsphenoidal surgery, thus identifying another hormone that influences CysC independent of renal function.

Cystatin C: a step forward in assessing kidney function and cardiovascular risk

The cardiorenal syndrome is a clinical manifestation of the bidirectional interaction between the heart and kidneys. Evaluating renal function is an essential part of the assessment of every cardiac patient. It has become clear that serum creatinine is not an accurate enough marker of glomerular filtration rate (GFR) and should not be used to evaluate kidney dysfunction. Creatinine-based estimates of GFR are preferred, but require renal function to be stable and are not suitable when changes in kidney function occur. Cystatin C (CysC) has been the target of much interest in the search for an alternative measure of GFR. As an endogenous biomarker, CysC possesses many of the properties required of a good marker of renal function. Compared with that of creatinine, plasma concentrations of CysC are less influenced by factors other than GFR. Consequently, CysC correlates with true GFR more accurately than creatinine. Equations for estimating GFR from CysC values have also been developed, which makes values easier to interpret and facilitates the clinical use of this new marker. The use of CysC in acute kidney injury has also shown promising results. CysC has been studied as a risk marker for prognosis in cardiovascular disease. This effect is attributed to the strong impact of renal dysfunction on progressive cardiovascular disease and impaired survival. Higher levels of CysC have consistently been predictive of incident or recurrent cardiovascular events and adverse outcomes. CysC is a predictor of the development of heart failure and increased levels of CysC have an independent association with higher mortality in both chronic and acute heart failure. In conclusion, CysC appears to be an interesting marker of renal function and is useful for risk stratification in heart failure.

Reference intervals and factors contributing to serum cystatin C levels in a Chinese population

BACKGROUND

Serum cystatin C (Cys-C), an inhibitor of cysteine proteases, has been suggested as an ideal biomarker of glomerular filtration rate (GFR).

OBJECTIVES

The objective of this study was to describe the reference intervals of serum Cys-C and identify factors associated with serum Cys-C or its variability, including age, gender, creatinine (Crea), blood urea nitrogen (BUN), and uric acid (UA).

DESIGN AND METHODS

Serum Cys-C, Crea, BUN, and UA were measured in 4,517 healthy participants aged 8-89 years attending our hospital. Serum Cys-C was analyzed using a latex-enhanced immunoturbidimetric method. Crea were tested by picric acid jaffe method, BUN, and UA by kinetic UV assays.

RESULTS

The predominant characteristic of Cys-C distribution was that Cys-C concentration in age ≥60 years group was the highest (P < 0.05). The differences of Cys-C concentration between males and females existed for subjects aged from 30 to 59 years (P < 0.05). In a multiple model adjusted only for gender and age, gender (β = 0.007) has stronger effect on Cys-C levels, compared with age (β = 0.003). The clinical variables, comprised of age, gender, Crea, BUN, and UA, involved in the fully adjusted equation accounted for 37.6% of variation of Cys-C.

CONCLUSIONS

Ninety-five percent reference intervals for healthy population were partitioned into three categories only by age, 0.59-1.07 mg/L for subjects aged 19-59 years; 0.74-1.14 mg/L for the older aged ≥60 years; and 0.63-1.11 mg/L for children aged ≤18 years. Serum Cys-C is significantly related to gender, age, UA, Crea, and BUN. Besides, there are still other factors contributing to variation of Cys-C levels.

Interpreting different measures of glomerular filtration rate in obesity and weight loss: pitfalls for the clinician

To combat the increasing incidence of obesity, much research has been devoted to devising successful strategies for weight loss, including manipulation of diet and gastric surgery. Obesity itself can be associated with renal dysfunction, and the degree of reversibility of this with weight loss has being studied. However, there are significant limitations and flaws in the methods we have available to measure glomerular filtration rate (GFR) in overweight and obese subjects. Obesity is associated with changes in body composition including lean and fat mass. This has implications for assumptions that underpin creatinine-based measures such as creatinine clearance, estimated GFR and other equations devised for obesity including the Salazar-Corcoran equation. These changes in body composition also affect measures of glomerular filtration such as cystatin C and nuclear medicine isotope scans. This article will review the accuracy of these current measures of renal function in the obese and consider the evidence for adjusting for body surface area or adjusting for lean body mass. Finally, the effect of weight loss itself on serial measurements of renal function in a given individual, independent of a true change in renal function, will be reviewed. Ultimately using the Cockcroft-Gault equation with an adjustment for lean body mass seems to be the best measure for renal function in obesity. No method for measuring renal function in situations of weight loss has been shown to be unequivocally superior.