Sodium Intake and Proteinuria/Albuminuria in the Population-Observational, Cross-Sectional Study

Sodium effects on proteinuria are debated. This observational, cross-sectional, population-based study investigated relationships to proteinuria and albuminuria of sodium intake assessed as urinary sodium/creatinine ratio (NaCR). In 482 men and 454 women aged 35–94 years from the Moli-sani study, data were collected for the following: urinary NaCR (independent variable); urinary total proteins/creatinine ratio (PCR, mg/g), urinary albumin/creatinine ratio (ACR, mg/g), and urinary non-albumin-proteins/creatinine ratio (calculated as PCR minus ACR) (dependent variables). High values were defined as PCR ≥ 150 mg/g, ACR ≥ 30 mg/g, and urinary non-albumin-proteins/creatinine ratio ≥ 120 mg/g. Urinary variables were measured in first-void morning urine. Skewed variables were log-transformed in analyses. The covariates list included sex, age, energy intake, body mass index, waist/hip ratio, estimated urinary creatinine excretion, smoking, systolic pressure, diastolic pressure, diabetes, history of cardiovascular disease, reported treatment with antihypertensive drug, inhibitor or blocker of the renin-angiotensin system, diuretic, and log-transformed data of total physical activity, leisure physical activity, alcohol intake, and urinary ratios of urea nitrogen, potassium, and phosphorus to creatinine. In multivariable linear regression, standardized beta coefficients of urinary NaCR were positive with PCR (women and men = 0.280 and 0.242, 95% confidence interval = 0.17/0.39 and 0.13/0.35, p < 0.001), ACR (0.310 and 0.265, 0.20/0.42 and 0.16/0.38, p < 0.001), and urinary non-albumin-proteins/creatinine ratio (0.247 and 0.209, 0.14/0.36 and 0.09/0.33, p < 0.001). In multivariable logistic regression, higher quintile of urinary NaCR associated with odds ratio of 1.81 for high PCR (1.55/2.12, p < 0.001), 0.51 of 1.62 for high ACR (1.35/1.95, p < 0.001), and of 1.84 for high urinary non-albumin proteins/creatinine ratio (1.58/2.16, p < 0.001). Findings were consistent in subgroups. Data indicate independent positive associations of an index of sodium intake with proteinuria and albuminuria in the population.

Association between cotinine-verified smoking status and moderately increased albuminuria in the middle-aged and older population in Korea: A nationwide population-based study

Objectives

Although several self-reported questionnaire-based studies have found an association between smoking and moderately increased albuminuria, this result remains controversial. We investigated whether moderately increased albuminuria was associated with smoking status, verified by urinary cotinine (an objective biomarker of tobacco exposure), using population-based, nationally representative data.

Methods

This study included 2059 participants aged ≥ 50 years from the 2014 Korean National Health and Nutrition Examination Survey. Individuals with a urinary cotinine level ≥ 50 ng/mL were identified as cotinine-verified smokers. Moderately increased albuminuria was defined as a urine albumin-to-creatinine ratio ranging between ≥ 30 mg/g and < 300 mg/g. Multivariable logistic regression was used to evaluate the association between cotinine-verified smoking status and moderately increased albuminuria.

Results

Among the study participants, 16.9% were cotinine-verified smokers, 84.8% of whom were men. After adjustment for multiple covariates, cotinine-verified smokers showed a significant positive association with moderately increased albuminuria (adjusted odds ratio: 4.37, 95% confidence interval: 1.63–11.71) compared with cotinine-verified non-smokers. The association between urinary cotinine and moderately increased albuminuria did not differ with age, sex, obesity, or comorbidities (P-value for interaction > 0.05 in all cases).

Conclusion

This large-scale observational study showed that cotinine-verified smoking is associated with moderately increased albuminuria in the Korean middle-aged and older general population, suggesting that smoking must be strictly controlled to reduce the risk of moderately increased albuminuria.

Association between alcohol intake and measures of incident CKD: An analysis of nationwide health screening data

To evaluate the association between alcohol intake and incident chronic kidney disease measures as well as the sex differences in this association, we analyzed health screening data of 14,190,878 adults who underwent health screening ≥3 times and had glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² and normal proteinuria at baseline. eGFR was calculated with the Chronic Kidney Disease Epidemiology Collaboration equation. Proteinuria was defined as ≥1+ dipstick proteinuria and low eGFR as <60 mL/min/1.73 m². The risk of incident proteinuria and low eGFR was analyzed with an extended Cox model with alcohol intake level as a time-varying determinant and the annual change of eGFR with generalized linear model. A J-shape association of alcohol intake with the incident proteinuria was observed in men (adjusted hazard ratio [aHR], 0.961, 95% confidence interval [CI], 0.953–0.970 in men drinking alcohol <10 g/day; aHR 1.139, 95% CI, 1.123–1.154 in men drinking alcohol ≥40 g/day, compared with non-drinking men), and a positive association was seen in women (aHR, 1.034, 95% CI, 1.023–1.044 in women drinking alcohol <10 g/day; aHR, 1.094, 95% CI, 1.034–1.158 in women drinking alcohol ≥40 g/day, compared with non-drinking women). In both sexes, an inverse association of alcohol intake with the annual eGFR decline and incident low eGFR was observed. This study observed a beneficial effect of moderate alcohol intake on incident proteinuria in men and a protective effect of alcohol intake of any amount on the annual eGFR decline and incident low eGFR in both sexes. The long-term implications of these observations need to be elucidated with future studies.

Review of biomarkers to assess the effects of switching from cigarettes to modified risk tobacco products

Context: One approach to reducing the harm caused by cigarette smoking, at both individual and population level, is to develop, assess and commercialize modified risk alternatives that adult smokers can switch to. Studies to demonstrate the exposure and risk reduction potential of such products generally involve the measuring of biomarkers, of both exposure and effect, sampled in various biological matrices.Objective: In this review, we detail the pros and cons for using several biomarkers as indicators of effects of changing from conventional cigarettes to modified risk products.Materials and methods: English language publications between 2008 and 2017 were retrieved from PubMed using the same search criteria for each of the 25 assessed biomarkers. Nine exclusion criteria were applied to exclude non-relevant publications.Results: A total of 8876 articles were retrieved (of which 7476 were excluded according to the exclusion criteria). The literature indicates that not all assessed biomarkers return to baseline levels following smoking cessation during the study periods but that nine had potential for use in medium to long-term studies.Discussion and conclusion: In clinical studies, it is important to choose biomarkers that show the biological effect of cessation within the duration of the study.

Medium-term follow-up of renal function in hypoxaemic congenital heart disease patients

Introduction Hypoxaemic congenital heart disease (CHD) patients are at higher risk of complications. The aim of this study was to compare and follow-up blood and 24-hour urine analytical data in hypoxaemic and non-hypoxaemic CHD patients.

METHODS

The inclusion criteria for this study were as follows: patients older than 14 years of age with a structural CHD with or without associated hypoxaemia.

RESULTS

In total, 27 hypoxaemic and 48 non-hypoxaemic CHD patients were included in order to compare blood and 24-hour urine analytical data. Among hypoxaemic patients, 13 (48.1%) were male, two (7.4%) had diabetes mellitus, one of whom was a smoker, one (3.7%) had systemic arterial hypertension, and 11 (40.7%) showed pulmonary arterial hypertension. The mean follow-up time was 3.1±1.9 years. Hypoxaemic CHD patients showed higher proteinuria concentrations (g/24 hours) (0.09 (0.07; 0.46) versus 0.08 (0.07; 0.1), p=0.054) and 24-hour albumin excretion rate (µg/min) (16.5 (11.2; 143.5) versus 4.4 (0.0; 7.6), p<0.001) compared with non-hypoxaemic CHD patients; however, no significant differences were found in the proteinuria levels and in the 24-hour albumin excretion rate in CHD patients with associated hypoxaemia, both at baseline and at follow-up. When divided into groups, hypoxaemic patients with palliative shunts showed significantly higher proteinuria concentrations compared with hypoxaemic patients not operated on or with Fontan procedures (p=0.01). No significant differences were seen in 24-hour proteinuria and 24-hour albumin excretion rate during the follow-up of patients with palliative shunts.

CONCLUSIONS

Hypoxaemic CHD patients have significant higher 24-hour proteinuria concentration and 24-hour albumin excretion rate compared with non-hypoxaemic CHD patients. Among hypoxaemic CHD patients, those with palliative shunts showed the highest 24-hour proteinuria concentrations.

Association of serum carotenoid levels with urinary albumin excretion in a general Japanese population: the Yakumo study

Background

Albuminuria is a risk factor for not only nephropathy progression but also cardiovascular disease. Oxidative stress may have a role in the positive association between albuminuria and cardiovascular disease.

Methods

This cross-sectional study investigated the associations of serum levels of carotenoids, which are dietary antioxidants, with albuminuria among 501 Japanese adults (198 men, mean age ± SD: 66.4 ± 10.0 years; 303 women, mean age ± SD: 65.4 ± 9.8 years) who attended a health examination. Serum levels of carotenoids were determined by high-performance liquid chromatography. Logistic regression analysis was used to estimate odds ratios (ORs) with 95% CIs for albuminuria after adjustment for age, body mass index, smoking habits, drinking habits, hypertension, diabetes mellitus, and dyslipidemia.

Results

Prevalence of albuminuria was 15.4% among men and 18.1% among women. Among women with albuminuria, geometric mean serum levels of canthaxanthin, lycopene, β-carotene, total carotenes, and provitamin A were significantly lower than those of normoalbuminuric women. Adjusted ORs for albuminuria among women in the highest tertiles of serum β-carotene (OR, 0.45; 95% CI, 0.20–0.98) and provitamin A (OR, 0.45; 95% CI, 0.20–0.97) were significantly lower as compared with those for women in the lowest tertile. There were no associations between serum carotenoids and albuminuria in men.

Conclusions

An increased level of serum provitamin A, especially serum β-carotene, was independently associated with lower risk of albuminuria among Japanese women.

Association of low aerobic fitness with hyperfiltration and albuminuria in men

PURPOSE

The purpose of this study was to evaluate the association of low aerobic fitness (AF), a quantitative phenotype primarily modified by physical activity, with the earlier markers of chronic kidney disease (CKD).

METHODS

Maximum oxygen uptake (VO2max), the best index of AF, was estimated in an apparently healthy population of 34,769 adults without known history of diabetes and/or hypertension, and its association with renal function and albuminuria was analyzed retrospectively. VO2max was estimated using a cycle ergometer. Glomerular filtration rate was estimated with the Modification of Diet in Renal Disease Study equation. Glomerular hyperfiltration was defined as estimated glomerular filtration rate above the age- and sex-specific 97.5th percentile. Albuminuria was detected with dipstick urinalysis on fast morning urine and defined as ≥1+.

RESULTS

VO2max levels were negatively correlated with the odds ratios of glomerular hyperfiltration in men (Ptrend = 0.039), not in women. VO2max was associated with glomerular hyperfiltration in young men (≤ the median age; Ptrend < 0.001), but not in old men. VO2max levels were negatively correlated with the odds ratio of albuminuria in men (Ptrend < 0.001), but not in women. These findings suggest that low AF may be associated with earlier markers of CKD in men. This association was not observed in women.

CONCLUSION

From the results of this study, it can be concluded that low AF may be a possible independent, modifiable risk factor for CKD in men.

Smoking and chronic kidney disease in healthy populations

The objective of this review is to explore the link between smoking and the development of chronic kidney disease (CKD) in generally healthy populations without pre-existing renal dysfunction such as diabetic nephropathy. Twenty-eight epidemiological studies concerning the renal effects of smoking in the general population were collected from the MEDLINE database and were reviewed for indications of proteinuria and/or the decline of glomerular filtration rate (GFR), and evaluated on the level of evidence and the quality of the study. Sixteen of the 28 studies were cross-sectional in design. Most articles had some weakness in scope, such as the 6 articles which did not fully exclude DM patients from the subjects, the 4 that did not consider the effects of ex-smoking, and the 3 that focused on only a small number of subjects. From these cases, it is difficult to draw firm conclusions. However, proteinuria or microalbuminuria was persistently high in current smokers; as much as 5-8% or 8-15% respectively, which was up to 2 to 3-times the rate of lifelong non-smokers. On the other hand, only 5 studies broader in scope detected any decline of GFR in smokers, while 9 other studies suggested a higher GFR in smokers than in non-smokers. Two good quality studies showed an even a significantly lower risk of a decreased GFR in smokers. These paradoxical CKD markers in smokers, i.e., a higher appearance of proteinuria with a higher GFR, could be a focus for further studies to reveal the underlying reasons for smoking-induced CKD. Workplaces may be an excellent place to study this subject since the long-term changes in renal function of smokers can be observed by collecting data in the annual health check-ups mandated at places of employment.

Relationship between visceral fat accumulation and urinary albumin-creatinine ratio in middle-aged Japanese men

OBJECTIVE

Chronic kidney disease including microalbuminuria relates to cardiovascular disease (CVD). Microalbuminuria is also known to be a marker of generalized endothelial dysfunction. The metabolic syndrome which encompasses visceral fat accumulation and various metabolic disorders, has also an increase in albuminuria and relates to CVD. However, the relationship between visceral fat accumulation and albuminuria remains to be defined. The present study investigated the relationship between visceral fat accumulation and urinary albumin-creatinine ratio (UACR) in Japanese men.

METHODS

This study group comprised 1990 Japanese male subjects, who were employees of a city office, had undergone annual health check-up. Urinary albumin was collected from a single spot urine specimen collected anytime between morning and afternoon. Visceral fat area was estimated (eVFA) by the bioelectrical impedance analysis method.

RESULTS

Log-UACR correlated with age, log-body mass index (BMI), log-waist circumference (WC), log-eVFA, log-adiponectin, blood pressure, serum lipids and hemoglobin A1c (HbA1c). Stepwise multiple regression analysis identified log-eVFA, as well as HbA1c, blood pressure, log-TG, and age, as a significant determinant of log-UACR. Moreover, subjects with eVFA > or = 100 cm(2) had significantly higher UACR than those with eVFA <100 cm(2), irrespective of BMI. UACR was significantly worse in subjects with high numbers of metabolic risk factors, and moreover in subjects with eVFA > or = 100 cm(2) than in those with eVFA <100 cm(2).

CONCLUSION

These results suggested that visceral fat accumulation is associated with an increase in UACR. Evaluation of both visceral fat accumulation and urinary albumin may be important for preventing atherosclerotic diseases.

Physical activity and albuminuria

Higher urinary albumin excretion predicts future cardiovascular disease, hypertension, and chronic kidney disease. Physical activity improves endothelial function so activity may reduce albuminuria. Among diabetics, physical activity decreases albuminuria. In nondiabetics, prior studies have shown no association. The authors explored the cross-sectional association between physical activity and albuminuria in 3,587 nondiabetic women in 2 US cohorts, the Nurses' Health Study I in 2000 and the Nurses' Health Study II in 1997. Physical activity was expressed as metabolic equivalents per week. The outcome was the top albumin/creatinine ratio (ACR) decile. Multivariate logistic regression was used. Secondary analyses explored the ACR association with strenuous activity and walking. The mean age was 58.6 years. Compared with women in the lowest physical activity quintile, those in the highest quintile had a multivariate-adjusted odds ratio for the top ACR decile of 0.65 (95% confidence interval (CI): 0.46, 0.93). The multivariate-adjusted odds ratio for the top ACR decile for those with greater than 210 minutes per week of strenuous activity compared with no strenuous activity was 0.61 (95% CI: 0.37, 0.99), and for those in the highest quintile of walking compared with the lowest quintile, it was 0.69 (95% CI: 0.47, 1.02). Greater physical activity is associated with a lower ACR in nondiabetic women.

Alcohol consumption and 5-year onset of chronic kidney disease: the AusDiab study

BACKGROUND

Excessive alcohol consumption is a risk factor for hypertension and stroke; however, evidence for an association with chronic kidney disease is conflicting.

METHODS

A total of 6259 adults >or=25 years of age, without a history of alcohol dependence, participating in baseline (1999-2000) and follow-up (2004-2005) phases of an Australian population-representative study (AusDiab) were the subject of this analysis. Alcohol consumption status and volume/frequency were collected by standardized interviewer administered questionnaires and self-administered food frequency questionnaires. The outcomes were as follows: (i) 5-year decline in estimated glomerular filtration rate (eGFR) >or=10%, with baseline eGFR >or= 60 and final eGFR <60 mL/min/1.73 m(2), and (ii) 5-year doubling of albumin to creatinine ratio (ACR) with final ACR >or= 2.5 (males)/>or= 3.5 (females) mg/mmol, in the absence of albuminuria at baseline.

RESULTS

Self-identification as a moderate or heavy, versus light, drinker was associated with elevated risk of albuminuria in males and females <65 years of age (OR, 95% CI: males 1.87, 0.99-3.52; females 2.38, 1.37-4.14). Odds of de novo eGFR <60 mL/min/1.73 m(2) were 0.34 (95% CI 0.22-0.59) and 0.68 (95% CI 0.36-1.27) in males and females, respectively, who were moderate-heavy drinkers. Alcohol intake of >or=30 g/day was associated with an increased risk of albuminuria after adjustment for age, sex and baseline kidney function (OR = 1.59, 95% CI 1.07-2.36), but a reduced risk of eGFR <60 mL/min/1.73 m(2) (OR = 0.59, 95% CI 0.37-0.95), compared with consumption of <10 g/day.

CONCLUSIONS

Moderate-heavy alcohol consumption may be an important modifiable risk factor for albuminuria in the general population. The natural history of alcohol-induced kidney damage and how this relates to markers of kidney function in the general population warrant further research.

Association between Cigarette Consumption and Proteinuria in Healthy Japanese Men and Women from an Occupational Population

The association between cigarette consumption and prevalence of mild proteinuria (30-99 mg/dl of albumin) was analyzed in 11,569 male and 4,715 female workers aged 18-67 yr recruited from an occupational population. Proteinuria was found in 274 (2.4%) of the total male workers and in 50 (1.1%) of the total females. Stepwise logistic regression analyses showed that sex, suspected diabetes mellitus, blood pressure (BP) and Brinkman Index (BI) levels (0, 1-199, 200-499, 500-799, 800-) were significantly related to proteinuria, and that the odds ratio of each BI level for proteinuria was 1.11 (C.I.: 1.01-1.67). In the subjects aged 50 yr or older, after excluding those suspected of having hypertension and/or diabetes mellitus, the odds ratio reached 1.37 (C.I.: 1.15-1.63), with the gender difference then no longer significant. The odds ratio for proteinuria was calculated as 5.44 (C.I.: 2.27-13.0) in male and female smokers having a BI of 500 or above and normal-high BP (130-139/85-89 mmHg) in comparison with nonsmokers having normal BP (<130/85 mmHg). These results suggest that heavy cigarette consumption represented by a BI of 500 or above is a risk factor of proteinuria even in healthy Japanese workers, particularly in those aged 50 yr or older and having normal-high BP.

Lifestyle factors, obesity and the risk of chronic kidney disease

BACKGROUND

Some lifestyle behaviors and obesity are risk factors for vascular disease, but their relation to kidney disease is uncertain.

METHODS

To determine whether physical inactivity, smoking, alcohol drinking and obesity are associated with the risk of chronic kidney disease, we examined data from a nonconcurrent cohort study of 9,082 U.S. adults, aged 30-74 years, who participated in the second National Health and Nutrition Examination Survey (NHANES II) from 1976 through 1980. By linking the NHANES II Mortality Study with the Medicare end-stage kidney disease registry, we identified 189 incident cases of either treated end-stage kidney disease or chronic kidney disease-related death through 1992.

RESULTS

The risk of chronic kidney disease was related to physical inactivity both with and without adjustment for age, sex, race and body-mass index. The adjusted relative risk (RR) of moderately active versus very active persons was 1.2 (95% confidence interval = 0.7-1.8), and of inactive versus very active was 2.2 (1.3-3.8). Risk was also related to smoking; the RR in smokers of 1-20 cigarettes a day versus never smokers was 1.2 (0.7-2.3), and in smokers of more than 20 cigarettes a day, the RR was 2.3 (1.3-4.2). The RR in morbidly obese (body-mass index >/= 35 kg/m2) compared with normal weight persons was 2.3 (1.1-4.9), but risk was not increased for those classified as overweight or obese. Obesity risk appeared largely mediated by diabetes and hypertension, whereas physical inactivity risk was only partly explained by these factors, and smoking risk was independent of them. Alcohol consumption was not related to chronic kidney disease.

CONCLUSIONS

These data suggest that physical inactivity, smoking and morbid obesity contribute to the risk of chronic kidney disease.

The relationship of cigarette smoking to end-stage renal disease

Cigarette smoking (CS) has been associated with augmented progression of nephropathies responsible for the 4 major causes of end-stage renal disease (ESRD) in the United States. CS has well-described ways by which it causes tissue injury in other organ systems and the mechanisms by which it adversely affects nephropathy progression might be similar. Therefore, exploring the mechanisms for CS-induced nephropathy or progression thereof might yield important insights into the general mechanisms by which some or most nephropathies progress to ESRD. In addition, CS can be discontinued and so is a potentially correctable risk factor for ESRD, a syndrome whose incidence continues to increase. Therefore, the mechanism(s) by which CS induces nephropathy progression is an important area of investigation.

Microalbuminuria, an integrated marker of cardiovascular risk in essential hypertension

This paper reviews the existing epidemiological and clinical evidence about the relationships of non-diabetic microalbuminuria with cardiovascular risk factors such as elevated blood pressure (BP), systolic particularly, cardiac hypertrophy, adverse metabolic status, smoking habits, elevated angiotensin II levels, endothelial dysfunction, acute and perhaps subclinical inflammation. Because of that unique property of reflecting the influence of so many clinically relevant parameters, microalbuminuria may legitimately be defined as an integrated marker of cardiovascular risk, an unique profile among the several prognostic predictors available to stratify risk in hypertensive patients. Recent cohort studies also showed associations with cardiovascular morbidity and mortality independently from conventional atherogenic factors. This behaviour, whose understanding still needs further elucidation, suggests to measure albuminuria and to screen patients at a higher absolute risk in whom preventive treatment is expected to be more beneficial than in those with a lower absolute risk.

Microalbuminuria is common, also in a nondiabetic, nonhypertensive population, and an independent indicator of cardiovascular risk factors and cardiovascular morbidity

OBJECTIVES

To assess the prevalence of microalbuminuria in the general population, especially in nondiabetic and nonhypertensive subjects, and its association with known cardiovascular risk factors and cardiovascular morbidity.

DESIGN

Cross-sectional cohort study.

SETTING

Inhabitants of the city of Groningen, the Netherlands.

SUBJECTS

All inhabitants, aged between 28 and 75 years, were send a postal questionnaire and a vial to collect an early morning urine sample (n = 85 421). Of these 40 856 subjects (47.8%) responded. Cardiovascular risk factors and morbidity were validated in a well defined nondiabetic and nonhypertensive group of 5241 subjects.

MAIN OUTCOME MEASURES

Microalbuminuria, self-reported cardiovascular risk and cardiovascular morbidity in the total study cohort, and additionally more detailed measurements in a subset of the total population.

RESULTS

Microalbuminuria (20-200 mg L-1) was present in 7.2% of the subjects and independently associated with age, gender, hypertension, diabetes, smoking, previous myocardial infarction and stroke. Some of these associations were already observed at albuminuria levels of 10-20 mg L-1. After exclusion of the diabetic and hypertensive subjects, microalbuminuria was still prevalent in 6.6% of the subjects.

CONCLUSIONS

Microalbuminuria appears to be common not only in the general population but also in a nondiabetic, nonhypertensive population and is independently associated with increased cardiovascular risk factors and cardio-vascular morbidity. Importantly, some of these associations are present at urinary albumin levels currently considered to be normal. These findings suggest that urinary albumin measurements may be useful in early risk profiling and prevention of cardiovascular disease in the population at large.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Influence of renal biomarker variability on the design and interpretation of occupational or environmental studies

OBJECTIVES

To quantify and identify sources of within- and between-subject variability of microalbumin, N-acetyl-beta-D-glucosaminidase (NAG) and alanine aminopeptidase (AAP), three biomarkers used for early detection of renal injury, and to assess the consequences of this variability for the design and power of epidemiological studies.

METHODS

Urinary excretion of microalbumin, NAG, AAP and creatinine as well as blood pressure (BP) were measured three times over a 2-year period among 142 healthy male workers. To minimise physiopathological and analytical sources of variation, standardised methods were used for urine collection and assays, and severe exclusion criteria were applied. At the first and third examinations, subjects completed the same questionnaire, providing information about their personal characteristics, tobacco and alcohol consumption, and health. A linear mixed model was used to estimate the within- and between-subject variance components and to analyse the relation between subjects' characteristics and the biomarkers.

RESULTS

No change in the mean value of any of the biomarkers was observed over the 2-year period. Intra-class correlation coefficients between repeated measurements were 0.53, 0.57 and 0.56 for microalbumin, NAG and AAP, respectively; the between-subject variance was slightly higher than the within-subject variance. Subjects' age, BP, body mass index and smoking and drinking habits explained 7.2%, 12.5% and 4.2% of the total variance of microalbumin, NAG and AAP, respectively.

CONCLUSIONS

In this healthy population of male workers, day-to-day differences in biomarker values appeared to be nearly as great as differences between subjects. The within-subject variance of these biomarkers is not high enough to justify systematic repeated measurements in epidemiological surveys. But, in some situations where the number of subjects is limited, measuring the subjects twice may improve study power by reducing the total variance by about 25% for each biomarker. Taking the above covariates into account would slightly improve study power and the accuracy of parameter estimates for NAG, but would add little to the analysis of microalbumin and AAP.

Microalbuminuria in essential hypertension

Microalbuminuria is frequently seen in patients with established essential hypertension, and is a predictor of a higher risk for cardiovascular and probably renal dysfunction. The presence of microalbuminuria has been shown to correlate with the other cardiovascular risk factors commonly seen in hypertensive patients. This fact indicates that the detection of an increased urinary albumin excretion could probably be the best index of an increased global cardiovascular risk in a given patient. Blood pressure control is accompanied by a fall in the content of albumin in urine. Agents with the capacity to block the renin-angiotensin system have shown a capacity to decrease urinary albumin excretion, which is independent of their ability to lower blood pressure. Whether or not a decrease in urinary albumin excretion is accompanied by an improved renal and cardiovascular prognosis in hypertensive patients remains to be elucidated.

Microalbuminuria predicts cardiovascular events and renal insufficiency in patients with essential hypertension

BACKGROUND

Some patients with essential hypertension manifest greater than normal urinary excretion of albumin (UAE). Authors of a few retrospective studies have suggested that there is an association between microalbuminuria and cardiovascular risk.

OBJECTIVE

To evaluate whether microalbuminuria is associated with a greater than normal risk of cardiovascular and renal events.

METHODS

We performed a retrospective cohort analysis of 141 hypertensive individuals followed up for approximately 7 years. Hypertensive patients were defined as having microalbuminuria if the baseline average UAE of three urine collections was in the range 30-300 mg/24 h.

RESULTS

Fifty-four patients had microalbuminuria and 87 had normal UAE. At baseline, the two groups were similar for age, weight, blood pressure, and rate of clearance of creatinine. Serum levels of cholesterol, triglycerides, and uric acid in patients with microalbuminuria were higher than levels in those with normal UAE, whereas levels of high-density lipoprotein cholesterol in patients with microalbuminuria were lower than levels in patient with normal UAE. During follow-up, 12 cardiovascular events occurred among the 54 (21.3%) patients with microalbuminuria and only two such events among the 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE (P = 0.003), cholesterol level (P = 0.047) and diastolic blood pressure (P = 0.03) were independent predictors of the cardiovascular outcome. Rate of clearance of creatinine from patients with microalbuminuria decreased more than did that from those with normal UAE (decrease of 12.1 +/- 2.77 versus 7.1 +/- 0.88 ml/min, P < 0.03).

CONCLUSIONS

This study suggests that hypertensive individuals with microalbuminuria manifest a greater incidence of cardiovascular events and a greater decline in renal function than do patients with normal UAE.

Smoking cessation does not change urinary albumin excretion in normal subjects

The aim of the study was to examine the effect of smoking cessation on urinary albumin excretion (UAE) in normal subjects. The study consisted of two parts. The first was a randomized 4-week study, in which 182 heavy smokers were asked to quit smoking immediately (n = 69, available for analysis) or to continue smoking for another 4 weeks (n = 70, available for analysis). After 4 weeks, the latter group was also asked to stop smoking. The second part was a non-randomized follow-up study comparing UAE in 33 unsuccessful and 57 successful quitters followed for 26 weeks. Measurements of UAE (ELISA) were taken from 24-h urine samples before smoking cessation, after 4 weeks, and after 26 weeks. After 4 weeks, no statistically significant change in UAE was found within each group or between quitters and smokers. The 95% confidence intervals of the change in log UAE were -7.4 to 9.9% of the initial value in the smoker group and -4.9 to 11.3% in the quitter group. In the second part of the study, after 26 weeks, a 16% increase (95% confidence interval 5.5 to 26.5%) in mean log UAE was found in the group that had stopped smoking (p < 0.003), but no statistically significant difference in UAE between continued smokers and quitters was found after adjusting for the baseline level (ANCOVA). In conclusion, smoking cessation seems to have no effect on UAE within the physiological range in normal subjects over an observation period of 4 weeks, and no sign of a decrease in UAE was seen after 26 weeks of smoking cessation.

Effect of smoking on the prevalence of albuminuria in Japanese men with non-insulin-dependent diabetes mellitus

Smoking is a risk factor for diabetic nephropathy in patients with IDDM and potentially those with NIDDM. We investigated the relationship between renal involvement and cigarette smoking in 148 men with NIDDM. The presence of renal involvement was assessed by determining the overnight urinary albumin/creatinine ratio (mg/g, ACR). The patients were divided into three groups, normo-, micro-, and macroalbuminuria, based on the ACR (< 30, 30-300, and 300 < or = mg/g, respectively). The incidence of micro-/macroalbuminuria in 81 smokers was significantly higher than that in 21 ex-smokers (stopped smoking at least 10 years prior to the study) or 40 non-smokers (53.1, 33.3, and 20.0%, respectively). The prevalence of smoking in the groups of patients with normo-, micro-, and macroalbuminuria were 45, 73, and 76%, respectively. The relative risk (odds ratio) for the prevalence of micro-/macroalbuminuria associated with smoking was 4.5 (95% CI, 1.9-11.6, P < 0.001) in smokers and was 2.0 (not significant) in ex-smokers. Our results indicate that stricter counselling about the importance of quitting smoking will be necessary in patients with NIDDM to protect against the development of diabetic nephropathy.

Increased transcapillary escape rate of albumin in elderly subjects due to long-term smoking habits

Transcapillary escape rate of albumin (TER) expressed as percentage decrease in specific activity of plasma albumin per hour was measured in 44 healthy male subjects, 10 young non-smokers (median age 24.0 years, range 21-33), 10 young smokers (30.5 years, range 27-36), 10 elderly non-smokers (64.0 years, range 51-75) and 14 elderly smokers (61.5 years, range 54-69). In addition urinary albumin excretion rates were measured in 15 of the elderly subjects. The subjects were investigated after overnight fasting and abstention from tobacco. Median TER was 7.33% (interquartile range 5.82-9.90) in the elderly smoking subjects. This value was significantly elevated as compared to elderly non-smokers, 4.47% (2.93-5.83), young non-smokers, 3.70% (2.24-6.30) and young smokers, 4.25% (2.80-4.44). A statistically non-significant (P = 0.064) tendency of a higher urinary albumin excretion rate was observed in elderly smokers. This agrees with other investigations showing slightly increased albuminuria in smokers compared with non-smokers. The differences were not related to differences in blood pressure, plasma cholesterol, weight, or abuse of alcohol in the elderly subjects. Diabetic subjects with an increased TER to levels comparable with levels in long-term smokers have increased urinary albumin excretion rates, which seems to be greater than in long-term smoking subjects. It is suggested that increased TER in long-term smokers may indicate a vascular dysfunction affecting either capillary permeability or endothelial surface area.

Atherosclerotic risk factors are increased in clinically healthy subjects with microalbuminuria

Increased morbidity and mortality from atherosclerotic vascular disease were observed in subjects with slightly elevated urinary albumin excretion rate (UAER), known as microalbuminuria. Therefore, the association between microalbuminuria and established atherogenic risk factors was studied in clinically healthy subjects. All healthy 40-65 year-old participants with microalbuminuria, examined within the first 21 months of The Copenhagen City Heart Study, were invited, and 28 were studied. An age- and sex-matched group of 60 randomly chosen subjects with normoalbuminuria served as control. Microalbuminuria was defined as a UAER of 6.6-150 micrograms/min, and normoalbuminuria as a UAER < or = 6.6 micrograms/min. In the microalbuminuric group, systolic and diastolic blood pressures were both elevated (mean (95% C.I.) 128 (123-134) vs. 119 (116-122) mmHg; P = 0.005, and 75 (71-78) vs. 69 (67-71) mmHg; P = 0.008, respectively), and serum apolipoprotein (apo) A-1 concentration was lower (1.30 (1.20-1.37) vs. 1.42 (1.36-1.47) milligrams; P = 0.02) in comparison with the normoalbuminuric group. Furthermore, serum HDL-cholesterol concentration tended to be lower, whereas body weight, body mass index and fasting serum insulin concentration were slightly elevated in the microalbuminuric group but not statistically significant. It is concluded that microalbuminuria in clinically healthy subjects is associated with increased levels of atherogenic risk factors. This may contribute to the increased vascular morbidity and mortality observed in these individuals.

Night blood pressure and cigarette smoking: disparate association in healthy subjects and diabetic patients

Cigarette smoking and diabetes are well known risk factors for cardiovascular disease. The relation of nocturnal blood pressure (BP) to cigarette smoking is unclarified. We examined ambulatory BP in 18 healthy smokers matched for sex and age to 18 non-smokers. Sixteen smoking type 1 diabetic patients matching 16 non-smoking patients with normal urinary albumin excretion were also investigated. None of the healthy subjects or diabetic patients had a clinic BP > 160/95 mmHg. Night BP (systolic/diastolic mmHg) in healthy smokers (mean +/- SD) 102 +/- 9/57 +/- 5 was lower than in healthy non-smokers 108 +/- 10/61 +/- 6 (p = 0.06/p < 0.05). The difference between smokers and non-smokers was most prominent in the 3 h period just before rising (99 +/- 9/57 +/- 6 versus 108 +/- 8/62 +/- 7, p < 0.01/p < 0.05). Daytime BP was similar between groups. The night/day ratio (%) of systolic (84 +/- 7) and diastolic (74 +/- 7) BP in healthy smokers was lower than in non-smokers (88 +/- 5 versus 80 +/- 5, p < 0.05 and p < 0.01) indicating an altered diurnal rhythm of blood pressure. No statistical significant difference was found for night or day BP in diabetic smokers versus non-smokers. The finding of a significantly lower BP in healthy (supine) smokers at night speaks against dysautonomia explaining the lower clinic BP found in epidemiological studies, as recently proposed. Alternatively a rebound effect or the existence of a substance with vasodilating properties in non-diabetic smokers is suggested.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of microalbuminuria in the general population

Microalbuminuria in the general population is associated with recognized risk factors for cardiovascular disease such as hypertension, hyperglycemia, hyperinsulinemia, and hyperlipidemia; and it is an independent predictor of subsequent cardiovascular mortality in hypertensive, diabetic, and elderly populations. Although different methods have been used for measuring and expressing urinary albumin excretion and a variety of cutoff levels have been used for defining microalbuminuria, prevalence of microalbuminuria appears to be higher in non-Europeans (8%-28%) than in Europeans (2%-10%). However, because of the large within-individual variability of urinary albumin excretion and the relatively low prevalence of microalbuminuria, large studies are required to detect statistically significant associations between albuminuria and cardiovascular risk factors. Evidence presented here supports the proposition that microalbuminuria represents a marker of cardiovascular disease risk in nondiabetic individuals as well as diabetic individuals. Moreover, because of a high sensitivity of the test and because albuminuria is a concomitant of many forms of renal disease, microalbuminuria also has a role in detecting patients with renal involvement associated with essential hypertension, lupus erythematosus, women with pre-eclampsia, and subjects with unsuspected primary and secondary nephropathies.