Do we need another equation to estimate GFR from serum creatinine in renal allograft recipients?

Preeclampsia and ESRD: The Role of Shared Risk Factors

BACKGROUND

Several registry-based studies, using diagnostic codes, have suggested that preeclampsia is a risk factor for end-stage renal disease (ESRD). However, because the 2 diseases share risk factors, the true nature of their association remains uncertain. Our goals were to conduct a population-based study to determine the magnitude of the association between preeclampsia and ESRD and evaluate the role of shared risk factors.

STUDY DESIGN

Population-based nested case-control study.

SETTING & PARTICIPANTS

The US Renal Data System was used to identify women with ESRD from a cohort of 34,581 women who gave birth in 1976 to 2010 in Olmsted County, MN. 44 cases of ESRD were identified and each one was matched to 2 controls based on year of birth (±1 year), age at first pregnancy (±2 years), and parity (±1 or ≥4).

PREDICTOR

Preeclamptic pregnancy, confirmed by medical record review.

OUTCOME

ESRD.

MEASUREMENTS

Prepregnancy serum creatinine and urine protein measurements were recorded. Comorbid conditions existing prior to pregnancy were abstracted from medical records and included kidney disease, obesity, diabetes, and hypertension.

RESULTS

There was evidence of kidney disease prior to the first pregnancy in 9 of 44 (21%) cases and 1 of 88 (<1%) controls. Per chart review, 8 of 44 (18%) cases versus 4 of 88 (5%) controls had preeclamptic pregnancies (unadjusted OR, 4.0; 95% CI, 1.21-13.28). Results were similar after independent adjustment for race, education, diabetes, and hypertension prior to pregnancy. However, the association was attenuated and no longer significant after adjustment for obesity (OR, 3.25; 95% CI, 0.93-11.37).

LIMITATIONS

The limited number of ESRD cases and missing data for prepregnancy kidney function.

CONCLUSIONS

Our findings confirm that there is a sizable association between preeclampsia and ESRD; however, obesity is a previously unexplored confounder. Pre-existing kidney disease was common, but not consistently coded or diagnosed.

Volume regression of native polycystic kidneys after renal transplantation

BACKGROUND

The natural course of native kidneys after renal transplantation (RT) or dialysis in patients with autosomal dominant polycystic kidney disease (ADPKD) remains poorly understood.

METHODS

We measured the total volumes of native kidneys and liver in 78 and 68 ADPKD patients, respectively, who had pre-transplant (within 2 years) and at least one post-transplant computed tomography (CT)/magnetic resonance imaging (MRI); in 40 patients with at least two post-transplant but no pre-transplant CT/MRIs; in 9 patients on chronic hemodialysis with at least one CT/MRI before and after beginning dialysis; and in 5 patients who had no image before and more than one image after dialysis. The last imaging was used in patients with multiple studies.

RESULTS

Mean total kidney volume (TKV) ( ± SD) prior to transplantation was 3187 ± 1779 mL in the 78 patients who had imaging before and after transplantation and decreased by 20.2, 28.6, 38.3 and 45.8% after 0.5-1 (mean 0.7), 1-3 (1.8), 3-10 (5.7) and >10 (12.6) years, respectively. In the multivariable analysis, time on dialysis prior to RT and time from baseline to transplantation were negatively associated with reduction in TKV, whereas estimated glomerular filtration rate (eGFR) after transplantation and time from transplantation were positively associated with percent reduction in TKV. In the 40 patients with imaging only after transplantation, TKV decreased by 3.2 ± 16.3% between 7.2 ± 6.0 and 11.2 ± 6.8 years after transplantation (P < 0.001). TKV was 11.2 ± 35.6% higher (P = NS) after a follow-up of 3.4 ± 2.0 years in the 9 patients with imaging before and after initiation of hemodialysis and 3.4 ± 40.2% lower (P = NS) in the 5 patients with imaging between 2.0 ± 2.1 and 3.5 ± 3.6 years after initiation of hemodialysis. In the 68 patients with liver measurements, volume increased by 5.8 ± 17.9% between baseline and follow-up at 3.7 ± 3.8 years after transplantation (P = 0.009).

CONCLUSIONS

TKV of native polycystic kidneys decreases substantially after RT. The reduction occurs mainly during the early post-transplantation period and more slowly thereafter.

Imaging classification of autosomal dominant polycystic kidney disease: a simple model for selecting patients for clinical trials

The rate of renal disease progression varies widely among patients with autosomal dominant polycystic kidney disease (ADPKD), necessitating optimal patient selection for enrollment into clinical trials. Patients from the Mayo Clinic Translational PKD Center with ADPKD (n=590) with computed tomography/magnetic resonance images and three or more eGFR measurements over ≥6 months were classified radiologically as typical (n=538) or atypical (n=52). Total kidney volume (TKV) was measured using stereology (TKVs) and ellipsoid equation (TKVe). Typical patients were randomly partitioned into development and internal validation sets and subclassified according to height-adjusted TKV (HtTKV) ranges for age (1A-1E, in increasing order). Consortium for Radiologic Imaging Study of PKD (CRISP) participants (n=173) were used for external validation. TKVe correlated strongly with TKVs, without systematic underestimation or overestimation. A longitudinal mixed regression model to predict eGFR decline showed that log2HtTKV and age significantly interacted with time in typical patients, but not in atypical patients. When 1A-1E classifications were used instead of log2HtTKV, eGFR slopes were significantly different among subclasses and, except for 1A, different from those in healthy kidney donors. The equation derived from the development set predicted eGFR in both validation sets. The frequency of ESRD at 10 years increased from subclass 1A (2.4%) to 1E (66.9%) in the Mayo cohort and from 1C (2.2%) to 1E (22.3%) in the younger CRISP cohort. Class and subclass designations were stable. An easily applied classification of ADPKD based on HtTKV and age should optimize patient selection for enrollment into clinical trials and for treatment when one becomes available.

Renal biomarkers for assessment of kidney function in renal transplant recipients: how do they compare?

Accurate assessment of renal function is of key importance, given its prognostic value. However, gold standard measures are cumbersome, and serum creatinine itself is an insensitive predictor, especially in renal transplant recipients. Though GFR-estimating formulae have been relied upon, they do have their own limitations. Nevertheless, renal biomarkers such as neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C, among others, are now emerging as potentially useful indicators of GFR. We aimed to evaluate the diagnostic performance of NGAL versus cystatin C and eGFR using CKD-EPI, MDRD and cystatin C in renal transplant recipients and non-transplant CKD patients. We found a significant correlation between NGAL, serum creatinine, cystatin C and eGFR. The latter parameters were also strong predictors of serum NGAL levels. However, performance of NGAL, based on receiver operating characteristic curves, was inferior to that of the reference tests. It appears that in renal transplant recipients NGAL correlates well with cystatin C and eGFR, most strongly with cystatin-based formula. Though this suggests potential use of NGAL as a screening test, its weaker diagnostic performance raises some concern about its clinical usefulness. Larger studies are needed to explore this further.

Risk factors for CKD in persons with kidney stones: a case-control study in Olmsted County, Minnesota

BACKGROUND

Kidney stones are associated with increased risk of chronic kidney disease (CKD); however, risk factors in the general community are poorly defined.

STUDY DESIGN

A nested case-control study was performed in residents of Olmsted County, MN, who presented with a kidney stone at the Mayo Clinic in 1980-1994 to contrast patients with kidney stones who developed CKD with a group that did not.

SETTING & PARTICIPANTS

Participants were selected from the Rochester Epidemiology Project, an electronic linkage system among health care providers in Olmsted County, MN. Cases were identified by diagnostic code for CKD and confirmed to have an estimated glomerular filtration rate < 60 mL/min/1.73 m(2). Controls were matched 2:1 to cases for age, sex, date of first kidney stone, and length of medical record.

PREDICTOR

Charts were abstracted to characterize stone disease, hypertension, diabetes, obesity, tobacco use, ileal conduit, symptomatic stones, type and number of stones, urinary tract infections, number and type of surgical procedures, and medical therapy.

OUTCOMES & MEASUREMENTS

Kidney stone patients with CKD were compared with matched stone patients without CKD.

RESULTS

There were 53 cases and 106 controls with a mean age of 57 years at first stone event and 59% men. In kidney stone patients, cases with CKD were significantly more likely (P < 0.05) than controls to have had a history of diabetes (41.5% vs 17.0%), hypertension (71.7% vs 49.1%), frequent urinary tract infections (22.6% vs 6.6%), struvite stones (7.5% vs 0%), and allopurinol use (32.1% vs 4.7%) based on univariate analysis.

LIMITATIONS

Potential limitations include limited statistical power to detect associations, incomplete data from 24-hour urine studies, and that stone composition was not always available.

CONCLUSION

As in the general population, hypertension and diabetes are associated with increased risk of CKD in patients with kidney stones. However, other unique predictors were identified in patients with kidney stones that increased the possibility of CKD. Further studies are warranted to elucidate the nature of these associations.

For estimating creatinine clearance measuring muscle mass gives better results than those based on demographics

Estimation of creatinine clearance requires knowledge of creatinine generation which can vary in different groups of patients. Since the main source of creatinine is muscle we used dual-energy X-ray absorptiometry to measure the mass of muscle in a cohort of adult men and women in Rochester, Minnesota. Serum and 24 h urinary creatinines were measured directly. The urinary creatinine was estimated using equations based on age and gender and muscle mass in order to calculate creatinine clearance. Among 664 subjects with a mean age of 55+/-20 years, 51% of whom were women, the model fit for urinary creatinine estimated with age and gender (R2=0.359) was similar to that estimated with measured muscle mass (R2=0.359). The likelihood of chronic kidney disease (creatinine clearance of less than 60 ml/min per 1.73 m2) in older subjects was highest with equations that used age, and likelihood of CKD in women was highest with equations that used gender. The outcomes of mortality and cardiovascular disease had stronger associations with decreased creatinine clearance calculated with age and gender than by the clearance calculated with muscle mass. This could be explained by age being a potent predictor of mortality and cardiovascular disease independent of urinary creatinine, muscle mass, and gender. Our study shows that the likelihood of chronic kidney disease in the elderly and in women and the risk of adverse outcomes may be inflated by equations that use patient demographics to estimate creatinine generation.

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.