Limitations of estimating glomerular filtration rate from serum creatinine in the general population

Association of CKD and cancer risk in older people

People with ESRD are at increased risk for cancer, but it is uncertain when this increased risk begins in the spectrum of chronic kidney disease (CKD). The aim of our study was to determine whether moderate CKD increases the risk for cancer among older people. We linked the Blue Mountains Eye Study, a prospective population-based cohort study of 3654 residents aged 49 to 97 yr, and the New South Wales Cancer Registry. During a mean follow-up of 10.1 yr, 711 (19.5%) cancers occurred in 3654 participants. Men but not women with at least stage 3 CKD had a significantly increased risk for cancer (test of interaction for gender P = 0.004). For men, the excess risk began at an estimated GFR (eGFR) of 55 ml/min per 1.73 m2 (adjusted hazard ratio [HR] 1.39; 95% confidence interval [CI] 1.00 to 1.92) and increased linearly as GFR declined. For every 10-ml/min decrement in eGFR, the risk for cancer increased by 29% (adjusted HR 1.29; 95% CI 1.10 to 1.53), with the greatest risk at an eGFR <40 ml/min per 1.73 m2 (adjusted HR 3.01; 95% CI 1.72 to 5.27). The risk for lung and urinary tract cancers but not prostate was higher among men with CKD. In conclusion, moderate CKD (stage 3) may be an independent risk factor for the development of cancer among older men but not women, and the effect of CKD on risk may vary for different types of cancer.

Kidney stones and the risk for chronic kidney disease

BACKGROUND AND OBJECTIVES

Kidney stones lead to chronic kidney disease (CKD) in people with rare hereditary disorders (e.g., primary hyperoxaluria, cystinuria), but it is unknown whether kidney stones are an important risk factor for CKD in the general population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Among Olmsted County, MN, residents, all stone formers (n = 4774) whose condition was diagnosed in 1986 through 2003 were matched 1:3 to control subjects (n = 12,975). Cox proportional hazards models adjusted for age, gender, and comorbidities (hypertension, diabetes, obesity, dyslipidemia, gout, alcohol abuse, tobacco use, coronary artery disease, heart failure, cerebral infarct, and peripheral vascular disease) were used to assess the risk for incident CKD defined as a clinical diagnosis (diagnostic codes), ESRD or death with CKD, sustained (>90 d) elevated serum creatinine (>1.3 mg/dl in men, >1.1 mg/dl in women), or sustained estimated GFR <60 ml/min per 1.73 m(2).

RESULTS

During a mean of 8.6 yr of follow-up, stone formers were at increased risk for a clinical diagnosis of CKD, but an increased risk for ESRD or death with CKD was NS. Among patients with follow-up serum creatinine levels, stone formers were at increased risk for a sustained elevated serum creatinine and a sustained reduced GFR.

CONCLUSIONS

Kidney stones are a risk factor for CKD, and studies are warranted to assess screening and preventive measures for CKD in stone formers.

Use of renal function measurements for assessing fracture risk in postmenopausal women

OBJECTIVE

To determine whether factors associated with moderate chronic kidney disease can be used to independently predict fracture risk in postmenopausal white women by analyzing the effect of adding renal function measurements to traditional risk factors (eg, age, body weight, bone mineral density) for fracture risk assessment.

PARTICIPANTS AND METHODS

In a prospective, population-based cohort study, postmenopausal women residing in Rochester, MN, with baseline measurements of bone mineral density and renal function were followed up for as long as 25 years for occurrence of fractures. Participants were enrolled in 1980-1984 or 1991-1993, and outcomes were analyzed in 2007. Standardized incidence ratios were used to compare the number of observed fractures with the number of predicted fractures, and potential risk factors were evaluated with Andersen-Gill time-to-fracture regression models.

RESULTS

During 5948 person-years of follow-up of 427 women, 254 women (59.5%) experienced a total of 563 fractures, 394 (70.0%) of which resulted from moderate trauma. Excluding incidentally diagnosed fractures, the 186 clinically diagnosed fractures were statistically undifferentiated from the 195 predicted fractures (standardized incidence ratio, 0.95; 95% confidence interval, 0.82-1.10). No significant trends were observed toward increasing fracture risk with inclusion of quintiles of declining renal function (P>.10). In univariate analyses, serum creatinine concentration, creatinine clearance rate, and estimated glomerular filtration rate were associated with greater risk of some fractures. In multivariate analyses, however, decreasing renal function was not found to be a significant risk factor, after adjusting for age, body weight, and bone mineral density.

CONCLUSION

The addition of serum creatinine concentration, creatinine clearance rate, or estimated glomerular filtration rate does not improve fracture risk prediction in postmenopausal white women who have moderate chronic kidney disease. This result can be partly explained by the fact that important risk factors for decreased renal function (eg, advanced age, lower body weight) are already accounted for in most fracture prediction models.

Diagnosis and management of chronic kidney disease

As the US population has continued to age, the number of patients with chronic kidney disease (CKD) has dramatically increased. Faced with this increase, clinicians need a better understanding of what an elevated serum creatinine level represents and a simple codified approach to evaluating renal failure. Creatinine, a muscle waste product, has an imperfect but predictable association with the glomerular filtration rate (GFR). Although other markers of GFR exist, including cystatin C, urea, inulin, and radioisotopic methods, their role in estimating GFR remains a matter for debate, especially that of cystatin C. Diagnosis and management of CKD are challenges for the nonspecialist. We describe a systematic approach that can be used by the nonspecialist to identify most but not all causes of renal insufficiency. Although this approach should allow for earlier recognition of treatable causes of CKD, it does not eliminate the involvement of a nephrologist in the care and management of the conditions causing the renal insufficiency. The nonspecialist should also be able to recognize the 9 therapies that are helpful in preservation of renal function in all patients with CKD.

Monitoring renal function and limitations of renal function tests

Chronic kidney disease (CKD) is a world-wide public health problem, with adverse outcomes of kidney failure, cardiovascular disease, and premature death. The National Kidney Foundation, through its Kidney Disease Quality Outcome Initiative (K/DOQI) and other National institutions, recommend glomerular filtration rate (GFR) estimates for the definition, classification, screening, and monitoring of CKD. Prediction equations based on serum creatinine values were chosen both for adults (Cockcroft-Gault [C-G] and Modification of Diet in Renal Disease [MDRD] study equations) and for children (Schwartz and Counahan-Barratt equations). This review aims to evaluate from recent literature the clinical efficiency and relevance of these equations in terms of bias, precision, and reproducibility in different specific indications (eg, screening CKD, assessment of disease progression, or therapy efficacy) in different populations. Because these prediction equations based on serum creatinine have limitations, especially in the normal or near-normal GFR range, kidney transplant recipients, and pediatric populations, other prediction equations based on serum cystatin C value were also considered as possibly more sensitive GFR surrogate markers. Recent guidelines state that the cystatin C-based prediction equation cannot be recommended for use in clinical practice. With prediction equations based on serum creatinine, the National Kidney Disease Education Program (NKDEP) recommendations are to report a numerical estimate in round numbers only for GFR values <60 mL/min per 1.73 m(2). The MDRD equation generally outperforms the C-G equation but may still have a high level of bias, depending on creatinine assay calibration, and low precision with, at best, approximately 80% of estimated GFR in the "accuracy range" of 70-130% of the measured GFR value, even in patients with known CKD. According to Kidney Disease Improving Global Outcomes (KDIGO) recommendations, many indications remain for GFR measurements using a clearance method. In that context, it should be recalled that radiolabeled-tracer plasma or urinary clearance methods, are safe, simple, accurate and reproducible.

Can we do better than a single estimated GFR threshold when screening for chronic kidney disease?

The Modification of Diet in Renal Disease (MDRD) equation has been used to screen for and diagnose chronic kidney disease (CKD). A fixed estimated glomerular filtration rate cutoff point has been advocated by the National Kidney Foundation to diagnose CKD. However, data derived from healthy individuals challenge this approach and suggest that age- and gender-specific reference values may be more useful in the screening setting.

Participation bias assessment in a community-based study of myocardial infarction, 2002-2005

OBJECTIVE

To compare the characteristics and survival of participants and nonparticipants in a community-based study of myocardial infarction (MI).

PARTICIPANTS AND METHODS

Residents of Olmsted County, MN, who presented with elevated cardiac troponin T levels from September 1, 2002, through December 31, 2005, were prospectively enrolled and classified with standardized criteria for MI. With specific Institutional Review Board approval, the medical records of patients with MI who did not provide consent but who had given general research authorization were reviewed, as was done for their consenting peers.

RESULTS

During the study period, 2277 individuals with elevated cardiac troponin T levels were approached, of whom 1863 (82 percent) consented to participate. Among the 414 nonparticipants, 375 (91 percent) had general research authorization. Of the 558 with general research authorization who met the criteria for incident (ie, first-ever) MI, 67 (12 percent) refused to participate. These participants tended to be older (mean plus or minus SD age, 71 plus or minus 14 vs 67 plus or minus 15 years; P equals .04), were more likely to be of races other than white (9 percent vs 2 percent; P equals .01), and had more comorbidities, including peripheral vascular disease (P equals .02), chronic pulmonary disease (P equals .06), heart failure (P equals .07), and impaired creatinine clearance (P equals .02). No significant differences were detected in cardiovascular risk factors or MI characteristics. During a median follow-up of 517 days, nonparticipants experienced increased mortality rates compared with participants (hazard ratio, 1.97; 95 percent confidence interval, 1.21 to 3.20), which was largely attributable to their older age and excess comorbidities (adjusted hazard ratio, 1.43; 95 percent confidence interval, 0.86 to 2.35).

CONCLUSION

In this community-based study of MI, nonparticipants experienced worse survival rates than participants largely because of differences in demographic and clinical characteristics. These differences should be kept in mind when interpreting study results, particularly if participation is low.

Metabolic syndrome and chronic kidney disease in a Chinese population aged 40 years and older

OBJECTIVE

To explore the relationship between metabolic syndrome and chronic kidney disease (CKD) in a study population from a developing country.

PARTICIPANTS AND METHODS

The prevalence of metabolic syndrome (as most recently defined by the International Diabetes Federation) and CKD (defined as an estimated glomerular filtration rate of < 60 mL/min per 1.73 m2 and/or albuminuria) was determined in 2310 study participants (age > or =40 years) from Beijing, China, between May 12 and December 7, 2004. The relationship between metabolic syndrome and CKD was then analyzed.

RESULTS

Participants with metabolic syndrome had a higher prevalence of CKD (15.4% vs 8.3%; P<.001) than those without the syndrome. As the number of metabolic syndrome traits increased, so did the prevalence of CKD. Strong unadjusted and adjusted associations were observed between metabolic syndrome and CKD. For participants without hypertension and diabetes, metabolic syndrome was also associated with CKD (odds ratio, 2.03; 95% confidence interval, 1.05-3.94).

CONCLUSIONS

In these 2310 Chinese study participants aged 40 years and older, metabolic syndrome was associated with CKD.

Understanding estimated glomerular filtration rate: implications for identifying chronic kidney disease

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) can be estimated using serum markers such as serum creatinine (SCr) or cystatin C. This review presents new insights into estimated GFR based on theory, validation studies, SCr assay standardization, cystatin C, and longitudinal comparison with measured GFR.

RECENT FINDINGS

The estimation of GFR by SCr differs in health and in chronic kidney disease (CKD) due to differences in GFR range and in creatinine production between these two populations. Among populations with normal baseline GFR, there is a more rapid decline in measured GFR than in SCr-based estimated GFR. While elevated SCr is specific for CKD, other disease processes may lead to elevated cystatin C. Validation is improved by refitting equation coefficients to compare populations, recognizing the asymmetry between estimated GFR and measured GFR, and using residual plots instead of Bland-Altman plots to assess bias.

SUMMARY

As a screening test, SCr should be interpreted as a marker of CKD probability in the context of the patient's clinical presentation. Measured GFR or creatinine clearance may be helpful in high-risk patients with normal SCr levels. GFR estimating equations should be reserved for patients with identified CKD. Standardized SCr and cystatin C assays are needed.