Screening for microalbuminuria: which measurement?

Microalbuminuria during acute coronary syndrome: Association with 22-year mortality and causes of death. The ABC-8* study on heart disease. (*ABC is an acronym for Adria, Bassano, Conegliano, and Padova Hospitals)

BACKGROUND

Microalbuminuria is associated with adverse outcomes in acute coronary syndrome (ACS) patients.

METHODS

To evaluate the very long-term association between Microalbuminuria and the overall mortality and causes of death in this clinical setting, we prospectively studied 579 unselected ACS patients admitted to three hospitals. The baseline albumin-to-creatinine ratio (ACR) was measured on days 1, 3, and 7 in 24-h urine samples. Patients were followed for 22 years or until death.

RESULTS

Virtually all patients completed follow-up; 449(78%) had died: 41% due to non-sudden cardiac death (non-SCD), 19% sudden cardiac death (SCD), 40% due to non-cardiac (non-CD) death. Using unadjusted Cox regression analysis, ACR was a significant predictor of all-cause mortality (hazard ratio [HR] 1.26;95%confidence interval [CI] 1.22-1.31; p˂0.0001) and the three causes of death (HR 1.40;95%CI 1.32-1.48; p˂0.0001), (HR 1.22;95%CI 1.12-1.32; p˂0.0001) and (HR 1.16;95%CI 1.09-1.23; p˂0.0001) for non-SCD, SCD and non-CD respectively. Using a fully adjusted model, ACR was a significant independent predictor of all-cause mortality (HR 1.12; 95%CI 1.08-1.16; p˂0.0001) and only non-SCD (HR 1.21; 95%CI 1.14-1.29; p˂0.0001). There was a positive interaction between ACR level and history of AMI (HR 1.15; 95%CI 1.03-1.29; p = 0.01) and the presence of heart failure at admission (HR 1.11; 95%CI 1.01-1.24; p = 0.04), and negative interaction with higher than median LVEF (HR 0.89; 95%CI 0.80-0.99; p = 0.03) for all-cause mortality at the multivariable level.

CONCLUSION

Based on the present analysis, baseline urinary albumin excretion during ACS is a strong independent predictor of the very long-term mortality risk, chiefly due to non-sudden cardiac death.

Study of microalbuminuria in chronic obstructive pulmonary disease patients at tertiary care teaching hospital

Background:

Hypoxemia-induced endothelial dysfunction leads to microalbuminuria. Microalbuminuria (MAB) has also been used as a parameter to assess the risk of cardiovascular events in an individual. The aim of this study was to observe the relationship of MAB in patients with chronic obstructive pulmonary disease (COPD) and to correlate MAB with different stages of COPD.

Materials and Methods:

This cross sectional study included 140 patients with COPD selected according to GOLD guidelines based on COPD test assessment score and the number of exacerbations who had smoking pack years of more than 10 years. Urine albumin creatinine ratio (UACR) more than 30 mg/gm represents MAB.

Results:

The UACR increases as the severity of groups of COPD increases with significant differences in UACR values among different COPD groups. Significant differences were seen among various groups of COPD when compared for different clinical parameters such as SPO2, PaO2, PaCO2, pH, and C-reactive protein (CRP). Pearson correlation analysis revealed that UACR was significantly inversely related with PaO2 (r = -0.514, P < 0.001), SPO2 (r = –0.397, P < 0.001) and FEV1 (r = –0.441, P < 0.001) and it was significantly positively correlated with PaCO2 (r = 0.675, P < 0.001).

Conclusion:

This study indicates that there is strong relationship of MAB in patients with COPD and the levels of MAB increase as the severity of COPD increases due to hypoxia and endothelial dysfunction. As MAB is a marker for cardiovascular risk, patients with COPD can be routinely evaluated for the urine test of MAB specially who are at increased risk for cardiovascular events.

Urinary adiponectin as a new diagnostic index for chronic kidney disease due to diabetic nephropathy

OBJECTIVE

The chronic kidney disease (CKD) is widely diagnosed on the basis of albuminuria and the glomerular filtration rate. A more precise diagnosis of CKD, however, requires the assessment of other factors. Urinary adiponectin recently attracted attention for CKD assessment, but evaluation is difficult due to the very low concentration of urinary adiponectin in normal subjects.

RESEARCH DESIGN AND METHODS

We developed an ultrasensitive ELISA coupled with thionicotinamide-adenine dinucleotide cycling to detect trace amounts of proteins, which allows us to measure urinary adiponectin at the subattomole level. We measured urinary adiponectin levels in 59 patients with diabetes mellitus (DM) and 24 subjects without DM (normal) to test our hypothesis that urinary adiponectin levels increase with progression of CKD due to DM.

RESULTS

The urinary adiponectin levels were 14.88±3.16 (ng/mg creatinine, mean±SEM) for patients with DM, and 3.06±0.33 (ng/mg creatinine) for normal subjects. The threshold between them was 4.0 ng/mg creatinine. The urinary adiponectin levels increased with an increase in the CKD risk. Furthermore, urinary adiponectin mainly formed a medium-molecular weight multimer (a hexamer) in patients with DM, whereas it formed only a low-molecular weight multimer (a trimer) in normal subjects. That is, the increase in urinary adiponectin in patients with DM led to the emergence of a medium-molecular weight form in urine.

CONCLUSIONS

Our new assay showed that urinary adiponectin could be a new diagnostic index for CKD. This assay is a non-invasive test using only urine, thus reducing the patient burden.

Pravastatin therapy during preeclampsia prevents long-term adverse health effects in mice

Preeclampsia (PE), associates with long-term increased risk for cardiovascular disease in women, suggesting that PE is not an isolated disease of pregnancy. It is not known if increased risk for long-term diseases is due to PE-specific factors or to prepregnancy renal and cardiovascular risk factors. We used a mouse model in which a WT female with normal prepregnancy health develops PE to investigate if preeclampsia causes long-term cardiovascular consequences after pregnancy for mothers and offspring. Mothers exhibited endothelial dysfunction and hypertension after PE and had glomerular injury that not only persisted but deteriorated, leading to fibrosis. Left ventricular (LV) remodeling characterized by increased collagen deposition and MMP-9 expression and enlarged cardiomyocytes were also detected after PE. Increased LV internal wall thickness and mass, increased end diastolic and end systolic volumes, and increased stroke volume were observed after PE in the mothers. Placenta-derived bioactive factors that modulate vascular function, markers of metabolic disease, vasoconstrictor isoprostane-8, and proinflammatory mediators were increased in sera during and after a preeclamptic pregnancy in the mother. Offspring of PE mice developed endothelial dysfunction, hypertension, and signs of metabolic disease. Microglia activation was increased in the neonatal brains after PE, suggesting neurogenic hypertension in offspring. Prevention of placental insufficiency with pravastatin prevented PE-associated cardiovascular complications in both mothers and offspring. In conclusion, factors that develop during PE have long-term, cardiovascular effects in the mother and offspring independent of prepregnancy risk factors.

Prevalent Rate of Nonalbuminuric Renal Insufficiency and Its Association with Cardiovascular Disease Event in Korean Type 2 Diabetes

BACKGROUND

Nonalbuminuric renal insufficiency is a unique category of diabetic kidney diseases. The objectives of the study were to evaluate prevalent rate of nonalbuminuric renal insufficiency and to investigate its relationship with previous cardiovascular disease (CVD) event in Korean patients with type 2 diabetes mellitus (T2DM).

METHODS

Laboratory and clinical data of 1,067 subjects with T2DM were obtained and reviewed. Study subjects were allocated into four subgroups according to the CKD classification. Major CVD events were included with coronary, cerebrovascular, and peripheral vascular events.

RESULTS

Nonalbuminuric stage ≥3 CKD group, when compared with albuminuric stage ≥3 CKD group, had shorter diabetic duration, lower concentrations of glycated hemoglobin, high density lipoprotein cholesterol, and high-sensitivity C-reactive protein, lower prevalent rates of retinopathy and previous CVD, and higher rate of treatment with angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers. Nonalbuminuric stage ≥3 CKD group showed a greater association with prior CVD events than no CKD group; however, albuminuric stage ≥3 CKD group made addition to increase prevalence of prior CVD events significantly when CKD categories were applied as covariates. Association of prior CVD events, when compared with normal estimated glomerular filtration rate (eGFR) and nonalbuminuria categories, became significant for declined eGFR, which was higher for eGFR of <30 mL/min/1.73 m², and albuminuria.

CONCLUSION

The results show that subjects with nonalbuminuric stage ≥3 CKD is significantly interrelated with occurrence of prior CVD events than those with normal eGFR with or without albuminuria. Comparing with normal eGFR and nonalbuminuria categories, the combination of increased degree of albuminuria and declined eGFR is becoming significant for the association of prior CVD events.

Establish Albumin-creatinine Ratio Reference Valueof Adults in the Rural Area of Hebei Province

Objective To establish albumin-creatinine ratio (ACR) reference value of the rural population in Hebei province.Methods This study enrolled 5154 participants. By excluding subjects with hypertension, diabetes, dyslipidemia, cardiovascular and cerebrovascular diseases, kidney diseases, and overweight condition, as well as those with an estimated glomerular filtration rate (eGFR)<60 ml/(min·1.73 m²), apparently healthy subjects (1168) were selected. Urine albumin was measured by using the immunoturbidimetic method, serum creatinine was measured by using Jaffe's kinetic method on a morning spot-urine sample, and ACR was calculated. The 95th percentile of ACR in the healthy subjects was used as the normal upper limit.Results The normal upper limit of ACR was 28.71 mg/g (3.25 mg/mmol) for males and 31.85 mg/g (3.60 mg/mmol) for females. Based on this ACR reference value, the age-gender standardized prevalence of albuminuria in the rural areas of Hebei province was 12.9%.Conclusion The ACR reference value in the rural of Hebei province is higher than that of the Western population.

Association of Renal Resistive Index, Renal Pulsatility Index, Systemic Hypertension, and Albuminuria with Survival in Dogs with Pituitary-Dependent Hyperadrenocorticism

An increased renal resistive index (RI) and albuminuria are markers of target organ damage secondary to systemic hypertension. This study evaluated associations between systemic blood pressure (SBP), renal RI, pulsatility index (PI), and albuminuria in dogs with pituitary-dependent hyperadrenocorticism (PDH). Predictors of overall mortality were investigated. Twenty client-owned dogs with PDH and 20 clinically healthy client-owned dogs as matched controls were included. Incidence rates of systemic hypertension (SBP ≥ 160 mmHg), albuminuria, and increased renal RI (≥ 0.70) and PI (≥ 1.45) in the control group were 5%, 0%, 5%, and 0%, respectively, compared to 35%, 40%, 50%, and 35%, respectively, in the PDH group (P = 0.001, P < 0.001, P < 0.001, and P = 0.001, resp.). No association between systemic hypertension, renal RI, renal PI, and albuminuria was observed. PDH was the only predictor of albuminuria and increased renal RI. Survival was not affected by increased renal PI, systemic hypertension, or albuminuria. Increased renal RI (≥ 0.70) was the only predictor of overall mortality in dogs with PDH.

The utility of microalbuminuria measurements in pediatric burn injuries in critical care

PURPOSE

Microalbuminuria, as measured by urinary albumin-creatinine ratios (ACRs), has been shown to be a marker of systemic inflammation and an indicator of the potential severity of trauma and critical illness. Severe pediatric burns represent the best model in which to investigate the clinical utility of microalbuminuria. This study aims to ascertain whether ACR measurements have any role in predicting the severity or the intensive care requirements in the critically unwell pediatric burn population.

MATERIALS AND METHODS

A retrospective observational study was undertaken within a regional burn center with a dedicated 8-bed burn intensive care unit (ICU). This looked at 8 years of consecutive pediatric burns requiring intensive care support-a total of 63 patients after exclusions. Daily urinary ACR measurements were acquired from all patients.

RESULTS

All patients had greater than or equal to 1 ACR measurement out with the reference range, and only 8% (5/63) presented to the ICU with a normal ACR. The median day for the peak ACR measurement was day 4. The relative lack of mortalities (3/63) precluded adequate correlations between ACR and outcomes. Peak and mean ACR values correlate well with length of ICU stay, and the peak ACR also correlates with total length of hospital stay and severity of burn injury as measured by total body surface area burnt and number of organ systems requiring support. No significant differences were found when the patients were stratified by age. The peak ACR measurement was found to be independently predictive of the length of the ICU stay. As such, we have created a predictive model to prove that an ACR that remains less than 12 mg/mmol is predicative of an ICU stay of less than or equal to 7 days.

CONCLUSIONS

The clinical utilities of ACR measurements are demonstrated by their correlation with the severity of injury, length of ICU stay, and requirements for multiple organ support. Albumin-creatinine ratios raised over certain thresholds highlight to the clinician the need for closer observation and the potential deterioration of patients.

Association of glycation gap with mortality and vascular complications in diabetes

OBJECTIVE

The "glycation gap" (G-gap), an essentially unproven concept, is an empiric measure of disagreement between HbA1c and fructosamine, the two indirect estimates of glycemic control. Its association with demographic features and key clinical outcomes in individuals with diabetes is uncertain.

RESEARCH DESIGN AND METHODS

The G-gap was calculated as the difference between measured HbA1c and a fructosamine-derived standardized predicted HbA1c in 3,182 individuals with diabetes. The G-gap's associations with demographics and clinical outcomes (retinopathy, nephropathy, macrovascular disease, and mortality) were determined.

RESULTS

Demographics varied significantly with G-gap for age, sex, ethnic status, smoking status, type and duration of diabetes, insulin use, and obesity. A positive G-gap was associated with retinopathy (odds ratio 1.24 [95% CI 1.01-1.52], P=0.039), nephropathy (1.55 [1.23-1.95], P<0.001), and, in a subset, macrovascular disease (1.91 [1.18-3.09], P=0.008). In Cox regression analysis, the G-gap had a "U"-shaped quadratic relationship with mortality, with both negative G-gap (1.96 [1.50-2.55], P<0.001) and positive G-gap (2.02 [1.57-2.60], P<0.001) being associated with a significantly higher mortality.

CONCLUSIONS

We confirm published associations of G-gap with retinopathy and nephropathy. We newly demonstrate a relationship with macrovascular and mortality outcomes and potential links to distinct subpopulations of diabetes.

Albuminuria prevalence in first morning void compared with previous random urine from adults in the National Health and Nutrition Examination Survey, 2009-2010

BACKGROUND

Albuminuria, defined as urine albumin/creatinine ratio (ACR) ≥30 mg/g, is a diagnostic component of chronic kidney disease (CKD). National estimates of ACR and CKD prevalence have been based on single random urine samples. Although 2 urine samples or a first morning void are known to produce different estimates of ACR, the impact of differing urine sampling schemes on nationally estimated rates of CKD is unknown.

METHODS

In 2009-2010, the National Health and Nutrition Examination Survey (NHANES) participants provided 2 untimed urine samples for sequential ACR measurement: an initial random urine collected in the NHANES mobile examination center and a subsequent first morning void collected at home. Rates of albuminuria were calculated in the overall population and broken down by demographics, diagnosed diabetes and hypertension status, and estimated glomerular filtration rate (eGFR).

RESULTS

Overall, 43.5% of adults with increased ACR (≥30 mg/g) in a random urine also had increased ACR in a first morning urine. This percentage was higher among individuals ≥50 years old (48.9%), males (53.3%), participants with diagnosed diabetes (56.3%) and hypertension (51.5%), and eGFR <60 mL/min/1.72m(2) (56.9%). The use of confirmed increased ACR (defined as the presence of ACR ≥30 mg/g in both samples taken within 10 days) to define CKD resulted in a lower overall prevalence (11.6%) than first morning urine (12.7%) or random spot urine only (15.2%).

CONCLUSIONS

ACR measured on random urine samples appears to overestimate the prevalence of albuminuria compared to first morning urine collections.

A Comparative Study of Clinical Utility of Spot Urine Samples with 24-h Urine Albumin Excretion for Screening of Microalbuminuria in Type 2 Diabetic Patients

Twenty-four hour urinary albumin excretion (UAE) is considered as gold standard method for albuminuria measurement, but collection of 24-h urine is inconvenient. The aim of present study was to evaluate whether albumin: creatinine ratio (ACR) and urinary albumin concentration (UAC) in different spot urine samples correlate or not with 24-h UAE for screening of microalbuminuria in type 2 diabetic patients. We collected first morning void (FMV), random urine sample (RUS) and 24-h urine, separately on consecutive days from 104 type 2 diabetic patients. ACR and UAC in each spot urine sample compared with 24-h UAE with regard to Pearson correlation coefficient. Pearson's correlation of albumin: creatinine ratio (ACR) with 24-h UAE was (r = 0.802 and 0.623) in first morning void (FMV) and random urine sample (RUS), respectively. Pearson's correlation coefficient of urinary albumin concentration (UAC) compared with 24-h UAE was (r = 0.943 and 0.920), in FMV and RUS, respectively, P < 0.01. Results revealed that values in first morning void (FMV) were better correlated with 24-h urinary albumin excretion (UAE), than the values in random urine sample (RUS). We conclude that the first morning void (FMV) may be able to replace 24-h urine collection, preferably urinary albumin concentration (UAC) in the initial screening of microalbuminuria in diabetic patients.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12291-011-0136-0) contains supplementary material, which is available to authorized users.

Microalbuminuria: causes and implications

Management strategies are increasingly focused on tackling the increasing burden of cardiovascular disease worldwide. Microalbuminuria is a powerful predictor of cardiovascular disease and mortality in adults. This holds true in the general adult population but is particularly recognized in those with diabetes, where it identifies those likely to develop progressive atherosclerotic vascular disease and renal impairment. The atherosclerotic process begins in childhood with likely consequences in later life. In-depth understanding of the mechanisms through which microalbuminuria occurs holds promise for designing therapies to arrest its development in the future. Microalbuminuria arises from increased leakage of albumin through the complex glomerular sieve known as the glomerular filtration barrier. This requires changes in the physio-chemical properties of components of this barrier. However, the increased glomerular permeability confirmed in disease does not necessarily correlate with recognized histological changes in the glomerulus, suggesting that perhaps more subtle ultrastructural changes may be relevant. The epidemiology of microalbuminuria reveals a close association between systemic endothelial dysfunction and vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria. This review discusses the mechanisms of microalbuminuria in disease, particularly the emerging role of the glomerular endothelium and its glycocalyx, and examines its implications for cardiovascular disease in the pediatric population.

Microalbuminuria in diabetes mellitus: Association with age, sex, weight, and creatinine clearance

Studies in the Western literature show a linear relationship between degree of microalbuminuria and body mass index (BMI), blood pressure, and duration of diabetes. This study was aimed to determine the correlation of microalbuminuria with age, sex, duration of diabetes, BMI, and creatinine clearance in type-2 diabetics in Indian population. One hundred patients (59 males and 41 females) with type-2 diabetes mellitus of duration six months or more and negative for albumin in urine by albustic method were included in the study. Detailed clinical history was taken followed by a thorough physical examination that included neurological examination in the selected patients. Micral test was used for estimation of microalbuminuria. Overall prevalence of microalbuminuria in the present study was 37%. Among the patients with microalbuminuria, 20 were males and 17 were females. Pearson correlation of microalbuminuria with age showed statistically significant linear relationship. Gender-wise correlation analysis of microalbuminuria failed to show any statistical significance. Correlation of microalbuminuria with BMI was also not significant (r = 0.063, P > 0.05). Creatinine clearance negatively correlated with microalbuminuria, but this was statistically insignificant. There was a statistically significant correlation of microalbuminuria with duration of diabetes. Prevalence of microalbuminuria is around 37% in type-2 diabetes mellitus. Incidence of microalbuminuria increases with age as well as with increased duration of diabetes mellitus. There is no effect of BMI and sex on the prevalence of microalbuminuria.

Microalbuminuria in normal Korean children

PURPOSE

Although microalbuminuria is known as a predictor of clinical nephropathy and cardiomyopathy, few studies have investigated the incidence and reference range of microalbuminuria in healthy children. This study aimed to establish a reference range and to study the age-related trend for spot urine microalbumin/creatinine ratio in a Korean pediatric population.

MATERIALS AND METHODS

352 healthy children were studied from July 2007 through March 2010. Height, weight, serum creatinine, spot urine microalbumin/creatinine ratio, and glomerular filtration rate (GFR) were obtained for each subject. We divided the study population into 5 groups according to age, and compared the spot urine microalbumin/creatinine ratio with other variables using one-way analysis of variance (ANOVA), regression analysis and Pearson's correlation analysis.

RESULTS

In this study, the data showed that the spot urine microalbumin/creatinine ratio decreased with age: 1-12 months, 22.72 ± 13.80 mg/mmol (2SD: 3.33-54.40 mg/mmol); 13-28 months, 16.34 ± 9.58 mg/mmol (2SD: 3.16-35.19 mg/mmol); 29-48 months, 13.12 ± 9.74 mg/mmol (2SD: 3.01-41.57 mg/mmol); 4-6 years, 10.58 ± 8.13 mg/mmol (2SD: 0.00-30.19 mg/mmol); and 7-19 years, 5.13±5.44 mg/mmol (2SD: 0.45-14.45 mg/mmol). The spot urine microalbumin/creatinine ratio showed correlation with age, height, height z-score, weight, weight z-score, GFR, body mass index (BMI) and body surface area (BSA).

CONCLUSION

The spot urine microalbumin/creatinine ratio in normal Korean children decreased with age. This ratio could potentially be used to establish reference ranges and cutoff values for Korean children and to predict nephropathy and cardiomyopathy.

Comparison of C-reactive protein and albumin excretion as prognostic markers for 10-year mortality after myocardial infarction

BACKGROUND

C-reactive protein (CRP) is an established prognostic marker in the setting of acute coronary syndromes. Recently, albumin excretion rate also has been found to be associated with adverse outcomes in this clinical setting. Our aim was to compare the prognostic power of CRP and albumin excretion rate for long-term mortality following acute myocardial infarction (AMI).

HYPOTHESIS

To determine whether albumin excretion rate is a better predictor of long-term outcome than CRP in post-AMI patients.

METHODS

We prospectively studied 220 unselected patients with definite AMI (median [interquartile] age 67 [60-74] y, female 26%, heart failure 39%). CRP and albumin-to-creatinine ratio (ACR) were measured on day 1, day 3, and day 7 after admission in 24-hour urine samples. Follow-up duration was 10 years for all patients.

RESULTS

At survival analysis, both CRP and ACR were associated with increased risk of 10-year all-cause mortality, also after adjusting for age, hypertension, diabetes mellitus, prehospital time delay, creatine kinase-MB isoenzyme peak, heart failure, and creatinine clearance. CRP and ACR were associated with nonsudden cardiovascular (non-SCV) mortality but not with sudden death (SD) or noncardiovascular (non-CV) death. CRP was not associated with long-term mortality, while ACR was independently associated with outcome both in short- and long-term analyses. At C-statistic analysis, CRP did not improve the baseline prediction model for all-cause mortality, while it did for short-term non-SCV mortality. ACR improved all-cause and non-SCV mortality prediction, both in the short and long term.

CONCLUSIONS

ACR was a better predictor of long-term mortality after AMI than CRP.

Cardiovascular and renal surrogate markers in the clinical management of hypertension

INTRODUCTION

Surrogate markers represent a significant contribution to early diagnosis, longitudinal prognoses, and outcome prediction in cases of hypertension. They often enable detection of disease and disease potential when the disease is still subclinical and are useful noninvasive tools for designing and evaluating therapeutic programs. Surrogate markers are increasingly employed as predictive endpoints for treatment.

METHODS

Key studies supporting the importance of surrogate markers as diagnostic and prognostic predictors of cardiovascular and renal clinical outcomes in hypertension, as well as what is known about the effects of renin-angiotensin-aldosterone system-blocking agents on these biomarkers were reviewed.

RESULTS

Clinical data supporting the use of surrogate markers for heart failure, such as brain natriuretic peptide (BNP) and N-terminal prohormone BNP; markers for renal function, such as urinary albumin to creatinine ratio (UACR), urinary albumin excretion rates (UAER), and creatinine, reflecting glomerular filtration; and markers of cardiac remodeling, such as left ventricular hypertrophy and calculations of left ventricular mass index (LVMI), were reviewed for their utility in improving prognosis and treatment efficacy. Finally, hypertension treatment with angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and potentially direct renin inhibitors can significantly improve outcomes predicted by surrogate markers.

CONCLUSIONS

BNP, UACR, UAER, and LVMI, among others, have been increasingly established as valid surrogate markers with significant value for hypertension prognosis and therapy. The benefits of using surrogate markers to gauge the effectiveness of hypertension therapy in reducing renal and cardiac complications can be seen in improved morbidity and mortality.

Protein and albumin-to-creatinine ratios in random urines accurately predict 24 h protein and albumin loss in patients with kidney disease

BACKGROUND

Random urine protein-to-creatinine (PCR) and albumin-to-creatinine (ACR) ratios have been proposed as alternatives to 24 h urine measurements to simplify sample collection and overcome errors. The aim of this study was to examine the ability of PCR and ACR to predict urinary 24 h protein and albumin loss, respectively, in patients with kidney disease, and determine the most appropriate time of collection.

METHODS

Eighty-three patients were recruited from a renal outpatient clinic. In a 24 h period, each collected an early-morning urine (EMU), second and third voids, and the remaining urine passed that day. PCR and ACR were determined in random urines and compared with the 24 h loss of protein and albumin, respectively.

RESULTS

For all patients, median (range) 24 h urine protein and albumin losses were 220 (30-15600) and 60 (<8-10,557) mg, respectively. Ratios derived from each of three random urines correlated well with 24 h protein or albumin loss (Spearman's r(s) > 0.87, P < 0.0001). Receiver operator characteristic (ROC) curve analysis showed PCR accurately predicted both an abnormal 24 h urine protein > or =150 mg/24 h (areas under curves [AUC] 0.90-0.92) and significant proteinuria above 300 mg/24 h (AUC between 0.97 and 1.00). ACR accurately predicted both an abnormal 24 h urine albumin > or =30 mg/24 h (AUC 0.98 to 0.99) and frank albuminuria at > or =300 mg/24 h or > or =700 mg/24 h (AUC between 0.99 and 1.00). EMU and random urines performed equally well in predicting proteinuria and albuminuria from PCR and ACR, respectively.

CONCLUSIONS

By careful choice of cut-offs, both PCR and ACR can be used in patients with kidney disease to rule in or rule out abnormal 24 h losses of protein and albumin. EMU and, importantly, random samples can be used as surrogates for 24 h urine collections.

How should proteinuria be detected and measured?

Proteinuria is a classic sign of kidney disease and its presence carries powerful prognostic information. Although proteinuria testing is enshrined in clinical practice guidelines, there is surprising variation among such guidelines as to the definition of clinically significant proteinuria. There is also poor agreement as to whether proteinuria should be defined in terms of albumin or total protein loss, with a different approach being used to stratify diabetic and non-diabetic nephropathy. Further, the role of reagent strip devices in the detection and assessment of proteinuria is unclear. This review explores these issues in relation to recent national and international guidelines on chronic kidney disease (CKD) and epidemiological evidence linking proteinuria and clinical outcome. The authors argue that use of urinary albumin measurement as the front-line test for proteinuria detection offers the best chance of improving the sensitivity, quality and consistency of approach to the early detection and management of CKD.

Audit of microalbumin excretion in children with type I diabetes

OBJECTIVE

To investigate prevalence, persistence and clinical correlates of increased microalbumin excretion in random urine samples collected in a paediatric diabetes clinic.

METHOD

Random urine samples were collected annually in patients >10 years attending the diabetes clinic in the Royal Hospital for Sick Children, Edinburgh. Albumin excretion is expressed as albumin:creatinine ratio (ACR) and classified as normal (10 mg/mmol), or macroalbuminuria (>47 mg/mmol in females, >35 mg/mmol in males). We analyzed retrospectively results on 421 urine samples collected from 217 patients (109 males), of a median age of 12.3 years (94% 10-16 years) over 3 years. For each sample, the corresponding mean HbA1c over the previous year was calculated.

RESULTS

Prevalence of micro- and macro-albuminuria in individual samples was 1% and 0.5% respectively. ACR was equivocal in 10.1% and 4.7% in samples from females and males respectively (p=0.03). HbA1c showed borderline significant differences across ACR groups (p=0.06). Equivocal ACR excretion was associated with slightly higher mean HbA1c (9.5±1.3%) compared to normal albuminuria (9.0±1.1%, p3.5 mg/mmol. The 14-16 years age group patients were most likely to have ACR >3.5 mg/mmol (p=0.05).

CONCLUSIONS

Female sex and increasing age, but not HbA1c, were independently associated with increased ACR. A robust mechanism for collection of repeat early morning urine samples from patients with increased ACR in random urine samples, and follow-up of those patients who have persistently high microalbumin excretion are important. It is also important to confirm the usefulness of ACR measurements in random urine samples as a marker of incipent nephropathy.

How to measure proteinuria?

PURPOSE OF REVIEW

To examine the use of urine total protein compared with albumin measurements to assess and monitor patients with chronic kidney disease.

RECENT FINDINGS

Urine albumin or total protein-to-creatinine ratio measurements on a single-voided specimen provide a convenient and reliable alternative to 24-h urine measurements. The majority of studies that inform current renoprotective strategies have relied upon urine total protein measurements. Urine albumin measurements are required to detect microalbuminuria. The proportion of urinary protein composed of albumin is variable and may depend on the underlying renal disease.

SUMMARY

Urine protein-to-creatinine measurements should continue to be used for the assessment and monitoring of patients with nondiabetic chronic kidney disease. Urine albumin-to-creatinine measurements should be reserved for detecting microalbuminuria and monitoring patients with diabetic nephropathy. Further research is required to investigate the relationship between urine total protein and albumin in different renal diseases and to compare the prognostic significance of urine total protein with that of albumin.

Clinical biochemistry guidelines in Wales: their impact on laboratory services

Background

Evidence of significant variations in clinical biochemistry practice in Wales led to the formation of the All Wales Clinical Biochemistry Audit Group (AWCBAG) in 1993, with the aim of auditing laboratory services to ensure that they are optimally used. As part of this process, clinical guidelines are produced and circulated to all clinical biochemistry departments in Wales. The current aim of the AWCBAG is to assess the extent and impact of adoption of these guidelines across Wales.

Methods

Three surveys were despatched at intervals over a decade to all clinical biochemistry departments in Wales to investigate practice in: (1) urine albumin testing to screen for diabetic nephropathy; (2) biochemical investigation of menopausal status and the monitoring of hormone replacement therapy; (3) screening for Cushing's syndrome.

Results

The results show that laboratories across Wales are generally following guideline criteria and are adapting their practice in-line with changing recommendations.

Conclusion

The introduction of AWCBAG guidelines has been widely accepted by clinical biochemistry departments in Wales. These guidelines have led to a more efficient and effective use of laboratory services.

Microalbuminuria and endothelial dysfunction: emerging targets for primary prevention of end-organ damage

A minor increase in urinary albumin excretion (microalbuminuria) is known to predict adverse renal and cardiovascular events in diabetic and hypertensive patients. Recent intriguing findings show that microalbuminuria is an early and sensitive marker of future cardiovascular events even in healthy subjects. The mechanisms linking microalbuminuria with end-organ damage have not been fully explained yet; however, generalized endothelial dysfunction might play an important role. Prevailing experimental and clinical data suggest that generalized endothelial dysfunction, frequently characterized by decreased nitric oxide bioavailability, actually precedes the development of microalbuminuria. This review summarizes the current knowledge about the intricate relationship between microalbuminuria and endothelial dysfunction. On the basis of the current evidence, we propose that microalbuminuria and endothelial dysfunction are an emerging target for primary prevention strategies in cardiovascular disease. In near future, dietary components improving nitric oxide bioavailability, such as cocoa-derived flavanols may play important role in these preventive strategies.

Hypertension-based clinical risk strategies for detecting microalbuminuria in diabetes

BACKGROUND

Microalbuminuria screening to identify patients at risk of diabetic nephropathy is widely accepted.

AIM

To investigate whether blood-pressure-based strategies can identify such patients without the need for microalbuminuria testing.

METHODS

Spot urine for albumin/creatinine ratios was performed in all patients over an 18-month period. The performance of four combinations of clinical models, based on existing triggers for anti-hypertensive intervention (prior use and/or existing systolic BP exceeding 140 or 160 mmHg and/or dipstick proteinuria exceeding 1+ or 2+) was evaluated at microalbuminuria thresholds of 3.5 and 10 mg/mmol. The models were ranked 1 to 4, based on their escalating relative strengths in predicting need for intervention.

RESULTS

Of 3748 patients, 1257 (34%) or 739 (20%) exceeded microalbuminuria thresholds of 3.5 or 10 mg/mmol. All four models predicted microalbuminuria risk (areas under ROC curves 0.60-0.77, all p < 0.001). The models (1-4) identified 2220, 2465, 2803 or 2937 for intervention, respectively, irrespective of microalbuminuria status, and missed 368, 232, 194 or 126 at 3.5 mg/mmol and 164, 87, 81 or 45 at 10 mg/mmol.

DISCUSSION

Clinical models using routinely measured parameters reduced the target population for microalbuminuria screening by 60-80%, missing 3-10% of patients with albumin/creatinine ratios exceeding 3.5 mg/mmol or 1-4% of those exceeding 10 mg/mmol.

Optimal bedside urinalysis for the detection of proteinuria in hypertensive pregnancy: a study of diagnostic accuracy

OBJECTIVE

To compare semi-quantitative visual and automated methods of urine testing with fully quantitative point of care urinalysis for the detection of significant proteinuria (0.3 g/24 hours) in pregnancy complicated by hypertension.

DESIGN

A prospective comparative study.

SETTING

A large teaching maternity hospital.

SAMPLE

One hundred and seventy-one pregnant women referred to the obstetric day-care unit for assessment of newly arisen hypertension.

METHODS

Early morning urine specimens were tested with four dipstick techniques (Multistix 8SG visual and automated and microalbumin/creatinine ratio visual and automated; Bayer, Elkhart, USA) as well as a fully quantitative measure of the microalbumin creatinine ratio with the DCA 2000 (a point of care assay for albumin; Bayer). These results were compared to a 24-hour urine protein measurement and measures of diagnostic accuracy/prediction are reported.

MAIN OUTCOME MEASURES

Significant proteinuria (> or =0.3 g/24 hours) measured by laboratory assay.

RESULTS

Automated dipstick urinalysis using the Clinitek 50 has significantly better predictive values for significant proteinuria (LR(+) 4.27, 95% CI 2.78 to 6.56; LR(-) 0.225, 95% CI 0.14 to 0.37) than conventional visual dipstick urinalysis (LR(+) 2.27, 95% CI 1.47 to 3.51; LR(-) 0.635, 95% CI 0.49 to 0.82). Dipstick microalbumin/creatinine ratio testing did not improve overall detection rates with automated or visual testing. Fully quantitative point of care measurement of albumin/creatinine ratio (ACR) was significantly better than any dipstick technique (LR(+) 14.6, 95% CI 6.74 to 31.8; LR(-) 0.069, 95% CI 0.030 to 0.16).

CONCLUSIONS

This study confirms that in pregnancy automated dipstick urinalysis is a more accurate screening test for the detection of proteinuria than visual testing. ACR testing can offer a significant improvement over conventional urinalysis if a fully quantitative method of detection is employed that uses pregnancy-specific thresholds. Dipstick assessment of ACR does not improve the detection rate of significant proteinuria.

Microalbuminuria in Hodgkin's disease

In some malignant disorders, it was reported that urinary albumin excretion (UAE) was correlated with the prognosis and the extent of the disease. In this study, 24-h UAE was determined in 34 Hodgkin's disease patients without prior treatment and 19 healthy controls. Microalbuminuria (MAU) was defined as UAE > or = 20 microg/min. In patients with MAU, UAE was determined again after the treatment. Mean UAE was 31.2 microg/min in the patient group and 5.6 microg/min in the controls (p = 0.005). Whereas MAU frequency was 47% in the patients, there was no MAU in the controls. Mean UAE tended to be higher in advanced stage patients compared to early stage patients (p = 0.051). Also, MAU frequency tended to be higher in the advanced stage group compared to the early stage group (p = 0.196). In four patients in whom remission could not have been achieved, although UAE was reduced, MAU did not disappear. In conclusion, UAE was increased in Hodgkin's disease. However, there is no significant correlation between UAE and the disease extent.

Microalbuminuria as a screening tool in cystic fibrosis-related diabetes

The improving longevity of cystic fibrosis (CF) subjects has resulted in an increased prevalence and duration of cystic fibrosis-related diabetes (CFRD). Microvascular complications were reported in CFRD. Microalbuminuria is well-established as a sensitive indicator of progression to diabetic nephropathy in non-CF diabetes, but confounding factors may make it less sensitive for CF subjects. We performed a cross-sectional study to look for the presence of microalbuminuria in samples from 40 CF subjects (34 without diabetes; CFND) attending the Exeter CF Clinic, compared with 43 nondiabetic, non-CF controls. The albumin-creatinine ratio (ACR) was raised in CF subjects both with (P < 0.001) and without (P < 0.0001) diabetes compared to controls. This reflected an increase in urinary albumin and a reduction in urinary creatinine in CF subjects. In single samples, microalbuminuria was present in 66.7%, 32.4%, and 15.4% of subjects in CFRD, CFND, and control groups. Repeat samples showed that 12% of CFND subjects and 17% of CFRD subjects met the criteria for a diagnosis of persistent microalbuminuria. In conclusion, CF subjects, even when not diabetic, have increased urinary albumin excretion due to chronic infection, and reduced urinary creatinine excretion due to low muscle mass. This results in subjects, who are not developing diabetic nephropathy, meeting the conventional criteria for microalbuminuria. We feel that further studies are required to clarify whether this measure is a useful tool to predict progression to diabetic nephropathy in subjects with CFRD.

Evaluation of measures of urinary albumin excretion in epidemiologic studies

Twenty-four-hour urinary albumin excretion (UAE) is considered the gold standard for determining albumin level in epidemiologic studies, but this measure is inconvenient and often unavailable. Simpler alternatives include the albumin:creatinine ratio (ACR) and urinary albumin concentration (UAC) obtained from a single sample. The authors assessed the strengths and weaknesses of ACR and UAC as alternatives to UAE using albumin measurements from two 24-hour urine samples collected in 1996-1999 from 4,678 participants aged 40-59 years in the International Study of Macronutrients and Blood Pressure (17 population samples from four countries). The authors compared ACR and UAC with regard to correlations with UAE, daily within-person variability, and associations with known predictors of UAE. Rank-order correlations of ACR with UAE were 0.949 and 0.942 for men and women, respectively, versus 0.881 and 0.816 for UAC. Mean within-person coefficients of variation were 34.0-40.0% for the three measures, with the smallest values being observed for UAC. Average correlations with blood pressure were similar for UAE, ACR, and UAC, but the correlation with body mass index was lower for ACR (0.118 for ACR and 0.188 for UAC vs. 0.211 for UAE) because of high correlation between body mass index and creatinine level. Thus, UAC and ACR are acceptable alternatives to the more complex UAE, and the simpler UAC may be preferable to ACR in some respects.

Uncertain clinical utility of contemporary strategies for microalbuminuria testing

AIMS

To determine whether conventional dipstick tests for proteinuria accurately identified patients with diabetic nephropathy and whether repeat testing for elevated albumin excretion and screening for urinary tract infection was required as part of the screening process for microalbuminuria.

METHODS

Random urine for albumin/creatinine ratio (ACR) was measured in all patients over a 6-month period. Patients who had a positive test (>3.5 mg/mmol) were requested to provide two further samples for re-testing and a mid-stream urine specimen to screen for asymptomatic bacteriuria. The evaluation of accuracy of dipstick proteinuria was carried out in the samples collected over a fixed 2-week period.

RESULTS

Dipstick vs. ACR--Of 221 samples collected, 142 were negative, 58 had 1+ and 21 had 2+ or more for dipstick proteinuria. At a threshold of 2+, the majority (81%) had ACR in the overt nephropathy range (>30 mg/mmol) and none had it below 10 mg/mmol, whereas at 1+, only 28% had ACR in the overt nephropathy range and 19% even had normoalbuminuria. Repeat Testing--Of the 1832 patients who had microalbuminuria measured, 673 had a positive test and 248 returned repeat samples. Eighty-one patients returned two samples, of which 16 had discordant results, and 161 patients gave three samples, of which only 23 were false positives. The majority of these 39 patients had low-grade microalbuminuria (ACR 3.5-10 mg/mmol) in their first sample. The absolute benefit of repeat testing was only to 3.4% of the population who screened positive, while in a further 2.3% (two-sample responders) there was potential for confusion because of discordant results. Infection Screening--Of the 248 samples, only 31 had evidence of urinary infection.

CONCLUSION

Dipstick proteinuria of 1+ does not necessarily represent significant nephropathy. There is little or no benefit in repeat testing outside of the low microalbuminuria range but compliance to such testing is poor. Screening for asymptomatic bacteriuria as part of microalbuminuria screening is of questionable value.

Absolute level and rate of change of albuminuria over 1 year independently predict mortality and cardiovascular events in patients with diabetic nephropathy

AIMS

To determine the nature of the association between baseline albuminuria and risk of all-cause mortality and cardiovascular disease, and to determine if the rate of change of albuminuria from baseline over 1 year predicts these endpoints in patients with diabetic nephropathy.

METHODS

Cohort study of 427 patients (161 Type 1 and 266 Type 2) with diabetic nephropathy defined as urinary albumin excretion (UAE) > or = 30 mg/24 h at baseline (mean age 53.4 years). Patients were recruited at the time of referral to a diabetic nephropathy clinic and followed up annually for an average of 5 years. UAE rate was re-measured at 1 year and the rate of change from baseline calculated.

RESULTS

All-cause mortality and cardiovascular disease increased significantly and continuously across quintiles of baseline UAE (P for linear trend < 0.001 in both outcomes). The rate of change of albuminuria over 1 year (log10) independently predicted all-cause mortality (hazard ratio (95% confidence interval) 1.76 (1.39, 3.11)) and cardiovascular mortality (1.57 (1.13, 5.22)). Taken as a categorical variable, a rate of change of albuminuria > or = 30% independently predicted mortality and cardiovascular events (2.07 (1.5, 4.30) and 1.89 (1.33, 4.06), respectively).

CONCLUSIONS

The rate of change of albuminuria over 1 year independently predicts mortality and cardiovascular disease in diabetic nephropathy and may have clinical utility as a risk marker in identifying a subgroup of patients at particular risk. The risk of these outcomes is continuous across the range of baseline albuminuria in patients with diabetic nephropathy.

Association of NAD(P)H oxidase p22 phox gene variation with advanced carotid atherosclerosis in Japanese type 2 diabetes

OBJECTIVE

To evaluate the association between the C242T polymorphism of the p22 phox gene, an essential component of NAD(P)H oxidase in the vasculature, with intima-media thickness (IMT) of the carotid artery and risk factors for atherosclerosis in type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

C242T polymorphism of the p22 phox gene was detected by polymerase chain reaction-restriction fragment-length polymorphism in 200 Japanese type 2 diabetic subjects and 215 nondiabetic subjects. We examined the association with this mutation and carotid atherosclerosis as well as the patients' clinical characteristics and the level of 8-hydroxy-2'deoxyguanosine (8-OHdG) as an index of oxidative DNA damage.

RESULTS

The diabetic subjects with the TC+TT genotypes displayed a significantly lower average IMT (1.13 +/- 0.31 vs. 1.31 +/- 0.34 mm; P = 0.0099) and a not significantly lower serum 8-OHdG level than those with the CC genotype, despite no difference in the risk factors. Stepwise multiple regression analysis showed that the risk factors for increased IMT in the diabetic subjects were systolic blood pressure (P = 0.0042) and p22 phox CC genotype (P = 0.0151). In nondiabetic subjects, the average IMT of the TC+TT group was not different from that of the CC group (0.85 +/- 0.14 vs. 0.94 +/- 0.30 mm, P = 0.417). Fasting plasma insulin concentration (41.4 +/- 15.6 vs. 64.2 +/- 59.4 pmol/l, P = 0.0098) and insulin resistance index of homeostasis model assessment (HOMA-R) (1.58 +/- 0.66 vs. 2.60 +/- 2.56, P = 0.0066) were significantly lower in the TC+TT group than in the CC group.

CONCLUSIONS

These results show that the C242T mutation in the p22 phox gene is associated with progression of asymptomatic atherosclerosis in the subjects with type 2 diabetes and is also associated with insulin resistance in nondiabetic subjects.

Left ventricular mass assessed by electrocardiography and albumin excretion rate as a continuum in untreated essential hypertension

OBJECTIVE

To study an association between albumin excretion rate and left ventricular mass (LVM) determined by electrocardiogram (ECG)-based criteria, and with respect to ambulatory blood pressure, in patients with newly diagnosed and never-treated essential hypertension.

METHODS

We measured 24 h ambulatory blood pressure, albumin excretion rate and LVM in 74 patients with newly diagnosed (within the past year) and never-treated essential hypertension, who were admitted to the hypertension clinic (Ulleval University Hospital). Albumin excretion rate was evaluated by determination of the albumin:creatinine ratio in the first-voided morning urine sample. LVM was assessed by ECG using Cornell voltage-QRS duration product and Sokolow- Lyon criteria.

RESULTS

Albumin excretion rate was significantly related to ambulatory blood pressure. There was a weak but significant negative correlation between the decrease in diastolic blood pressure during the night and the rate of excretion of albumin. The patients classified as dippers had a significantly lower albumin excretion rate compared with the non-dippers (1.36+/-0.83 compared with 1.68+/-0.87 mg/mmol; P = 0.03). LVM was found to be significantly related to ambulatory blood pressure. A weak relationship was observed between albumin excretion rate and LVM as evaluated by Cornell criterion (r = 0.23, P = 0.045). When only normoalbuminuric patients were included (i.e. four patients with microalbuminuria were excluded), the relationship was stronger (r = 0.36, P = 0.002).

CONCLUSIONS

The present findings show a continuous relationship between albumin excretion rate, LVM and ambulatory blood pressure in newly diagnosed patients with essential hypertension, and suggest the occurrence of early effects on target organs (kidneys and heart). These associations were observed using easily applicable methods such as ECG monitoring and determination of the albumin:creatinine ratio in morning urine samples.

The clinical application of a urine albumin:creatinine ratio point-of-care device

INTRODUCTION

Microalbuminuria is an accepted predictive marker for the early detection of renal disease and the identification of patients at high risk of developing complications of diabetes and hypertension. The Bayer Clinitek 50 is a urine chemistry point-of-care analyser for the semi-quantitative measurement of albumin and creatinine and calculation of albumin:creatinine ratio (ACR).

METHOD

Urine samples were obtained from 252 consecutive patients attending a city center diabetic clinic, and from 40 patients on admission to the ICU. Albumin and creatinine measurements were carried out using the Clinitek 50 and by the central laboratory.

RESULTS

The Clinitek 50 results agreed with the central laboratory results in 89% of the diabetic patient samples and 80% of the ICU patient samples. Excluding samples defined as normal by the Clinitek 50 (ACR<3.4 mg/mmol) would have resulted in an 80% reduction in samples sent to the lab for further quantification. The average length of stay in the group of ICU patients with normal ACR was significantly less than for those patients with an abnormal ACR (p<0.005).

CONCLUSIONS

The Clinitek 50 provides useful, immediate clinical information regarding the microalbuminuria status for use in the diabetic clinic setting or as a potential immediate risk management tool in intensive care.

[Prevalence of microalbuminuria and association with cardiovascular risk factors in a Spanish Mediterranean area]

BACKGROUND

The primary objective of this study was to know the prevalence of microalbuminuria (mAlb)in a general population from the Spanish Mediterranean area along with its association with other cardiovascular risk factors (CRF).

PATIENTS AND METHOD

We studied 99 consecutive patients who were classified in mAlb+ or mAlb-,depending on whether their mAlb was higher or lower than 30 mg/day,respectively.

RESULTS

Thirty-seven patients(9.3% of the general population) were mAlb positive. Twenty-one percent of them were males with hypertension. The presence of mAlb was positively correlated with age, systolic blood pressure,body mass index, waist-to-hip ratio, pulse pressure, HDL cholesterol,triglycerides, glycemia and serum creatinine. The level of mAlb was 12.9 (11.2) (mg/day) in non-hypertensive non diabetic individuals,while it was 14.1 (16.5) in diabetic non-hypertensive subjects, 22.5 (53,5) in hypertensive non-diabetic subjects and 27.7 (49.1)in diabetic individuals who were also hypertensive. Hypertension correlationed with the presence of mAlb with an odds ratio of 2.4 (CI 95%: 1.1-5.2)and the addition of a male gender increased the odds ratio to 3.8 (CI 95%: 1.8-8.1).

CONCLUSIONS

The prevalence of mAlb in the Spanish Mediterranean area appears to be low (9.3%),although it is especially high in hypertensive males with or without diabetes.

Predisposition to nephropathy in Polynesians is associated with family history of renal disease, not diabetes mellitus

AIMS

Familial clustering of diabetes and nephropathy suggests that either common environmental or inherited mechanisms are important in developing diabetic nephropathy. If an inherited mechanism is important, the albumin excretion rate might be increased in those at future risk. This study aimed to determine whether people with a family history of diabetes or people with a family history of renal disease were most at risk.

METHODS

In a two-by-two factorial study of urinary albumin in non-diabetic Polynesians, 90 people with a first degree relative (FDR) with end-stage renal failure (ESRF) and diabetes (group 1) were compared with 90 people with a FDR with non-diabetic ESRF (group 2), with 90 people with a FDR with diabetes but no known nephropathy (group 3) and 90 people with no known relatives with either diabetes or nephropathy (group 4). Groups were matched for ethnicity and age.

RESULTS

Subjects with a family history of ESRF (groups 1 and 2) had an increased mean albumin-creatinine ratio (1.25 vs. 1.00 mg/mmol, P = 0.01), but in subjects with a family history of diabetes (groups 1 and 3), the mean ratios were not significantly different from those without a family history of diabetes (1.06 vs. 1.17 mg/mmol; P = 0.2). In those with a family history of nephropathy, fasting blood glucose and systolic blood pressure were increased, while fasting insulin and 2 h insulin concentrations were lower. A family history of diabetes was associated with an increased fasting blood glucose and 2-h blood glucose. By multiple linear regression, the mean systolic blood pressure (P = 0.02), the 2-h glucose concentration (P = 0.05), a family history of renal failure (P = 0.04), female sex (P = 0.0001) and the total cholesterol (P = 0.01) were each independently associated with microalbuminuria, while a family history of diabetes was not (P = 0.09).

CONCLUSIONS

These data suggest that among Polynesians there is no specific inherited tendency to diabetic nephropathy per se. The risk of nephropathy does not appear to be associated with the degree of familial risk of diabetes itself. Rather, the risk of diabetic nephropathy may be the result of a familial risk of nephropathy from any cause and is associated with diabetes through relative hypoinsulinaemia and hyperglycaemia.

Increased urinary albumin excretion rate in breast cancer patients

A high frequency of slightly increased urinary albumin excretion (UAE) has been reported in patients with malignancies. Earlier studies have indicated a prognostic significance of UAE in some malignant diseases. We measured urinary albumin in 24-h urine samples in 44 patients with newly diagnosed early breast cancer and in 22 patients with relapse of metastatic breast cancer disease. The prevalence of microalbuminuria ( > or = 20 microg/min) was 20.5% in patients with early breast cancer and 54.5% in patients with metastatic disease. Median UAE was significantly higher in patients with metastatic breast cancer compared with the early breast cancer group (20.5 microg/min vs. 9.2 microg/min; p < 0.01). In patients with metastatic breast cancer, univariate survival analysis revealed a significantly lower survival rate in patients with microalbuminuria compared with the normoalbuminuric group (p <0.001). The present study demonstrates a high frequency of microalbuminuria in patients with breast cancer. Increased UAE was most prevalent in patients with metastatic disease. Our results also suggest that UAE may be a prognostic marker in metastatic breast cancer. Further prospective studies with a larger number of patients and controls are needed to test the validity of these observations.

Urinary albumin excretion and transcapillary escape rate of albumin in malignancies

Transcapillary escape rate of albumin was determined in 22 patients with different malignancies. In addition, urinary albumin excretion rate was measured in 24-h urine samples using a sensitive immunoassay. Increased urinary albumin excretion was defined as >/=20 microg/min according to conventional standards. Renal glomerular filtration and tubular function was estimated by 51Cr-EDTA plasma clearance and urinary beta 2-microglobulin, respectively. Median urinary albumin excretion rate was 15.0 microg/min (range 6-510 microg/min) and the frequency of increased urinary albumin excretion was 41%. This agrees with other studies showing increased albuminuria in several types of malignant diseases. Patients with advanced disease (tumour, node, metastasis (TNM) stage II-IV) had a significantly higher urinary albumin excretion rate than patients with localized disease (TNM stage I). Serum creatinine, glomerular filtration rate and urinary beta 2-microglobulin were all within normal limits. Median transcapillary escape rate of albumin was 5.5 %/h (range 2-8 %/h) and this level is comparable with values in healthy subjects. There was no significant difference in transcapillary escape rate between patients with elevated urinary albumin excretion and the normoalbuminuric group. Median value of the absolut outflux of albumin was 10.6 g/h with similar levels in patients with increased urinary albumin excretion and patients with normoalbuminuria. Our results indicate a high prevalence of minor glomerular dysfunction with a slightly elevated urinary albumin excretion in patients with malignancies. The normal endothelial function, as estimated by the transcapillary escape rate of albumin, suggests an overall unaffected capillary permeability and increased urinary albumin loss appears to be an isolated renal phenomenon in cancer patients.

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.

Risk factors for the progression of microalbuminuria in Japanese type 2 diabetic patients--a 10 year follow-up study

To clarify risk factors for the progression of microalbuminuria in Japanese type 2 diabetic patients, the longitudinal study for 10 years was conducted on 67 outpatients with type 2 diabetes, who had shown no overt proteinuria at baseline. The urinary albumin index (UAI) has been determined based on the mean of at least two random urine samples each year. Categories were defined as normoalbuminuria (UAI < 30.0 mg/g x Cr.), microalbuminuria (30.0 < or = UAI < 300.0), and macroalbuminuria (UAI > or = 300.0). Progression was defined as worsening of the category and/or more than doubling of the baseline UAI value. Multiple logistic regression analysis was performed using age, duration of diabetes, HbA1c, blood pressure, BMI, serum lipids, smoking habits, and alcohol consumption as independent variables and the progression of microalbuminuria as a dependent variable. Age and HbA1c were estimated as significant and independent variables. Furthermore, genetic polymorphisms of angiotensin I-converting enzyme (ACE) and angiotensinogen were analyzed to evaluate the genetic contribution. The D/D genotype of ACE was significantly more common in progressors than in non-progressors. These results suggest that glycemic control and age are important risk factors and the D/D genotype of ACE acts as a risk factor for the progression of microalbuminuria in Japanese type 2 diabetic patients.

Diabetic nephropathy

Diabetic nephropathy remains a leading cause of end-stage renal disease (ESRD) in western societies, accounting for over one-third of all patients beginning renal replacement therapy. Patients with Type 2 diabetes comprise the largest and fastest-growing single disease group requiring renal support therapy. In addition to the high risk of progression to ESRD, diabetic nephropathy is associated with a very high risk of cardiovascular morbidity and mortality, which is not abolished by dialysis and renal transplantation. While the prognosis of patients with diabetic nephropathy has considerably improved, a greater focus has recently been placed on treating diabetic patients early in order to prevent future organ failure. Microalbuminuria is an important intermediary end-point that correlates strongly with future advanced renal disease and cardiovascular mortality. Recent evidence indicates that optimum glycaemic control, tight blood pressure control, and the regular screening for and early treatment of microalbuminuria are necessary to prevent the development and progression of diabetic renal disease. By utilizing such strategies, the challenge is to reduce the cumulative incidence of overt nephropathy, with its associated increase in cardiovascular mortality, and the requirement for renal support therapy. Over the next 5-10 years, the patient with Type 2 diabetes will need to be the specific focus of such preventive treatment modalities.

Blood pressure control, microalbuminuria and cardiovascular risk in Type 2 diabetes mellitus

Type 2 (noninsulin-dependent) diabetes mellitus (DM) affects about 3% of the UK population. Diabetes often coexists with a cluster of other potent cardiovascular risk factors, including hypertension, dyslipidaemia and increased tendency for thrombosis, and increases the risk of early death from cardiovascular causes by about threefold. Microalbuminuria or proteinuria also may be present, further increasing the risk of cardiovascular mortality. Cardiovascular risk factors must be treated aggressively in patients with Type 2 diabetes and control of blood pressure at 140/85 mm Hg or lower is a priority. The management of hypertension in patients from some ethnic groups demands special consideration because they have a high incidence of diabetes and hypertensive complications. Patients must be urged to adopt appropriate lifestyle changes in the first instance but additional drug treatment for hypertension is usually required. All the major classes of antihypertensive agents lower blood pressure in Type 2 diabetic patients but have different effects on metabolic risk factors in different ways. Low-dose thiazide diuretics, beta-blockers, calcium channel blockers and angiotensin converting enzyme (ACE) inhibitors have been shown to reduce cardiovascular risk. Individually, the effects of low-dose thiazide diuretics and beta-blockers on glucose and lipid metabolism is clinically insignificant, though in combination much larger metabolic effects are seen. ACE inhibitors and calcium channel blockers have no, or small, beneficial effects on glucose and lipid metabolism, while the greater beneficial effects of alpha1-blockers on lipid profiles may render them especially useful in the Type 2 diabetic patient. Long-acting calcium-channel blockers and ACE inhibitors protect renal function and are suitable as first line therapy in patients with microalbuminuria or proteinuria. Until results from the current batch of randomized, placebo-controlled trials comparing different classes of antihypertensive agents are available, the choice of antihypertensive agent is difficult. Addressing overall cardiovascular risk factors, rather than hypertension alone, is essential in the management of the hypertensive Type 2 diabetic patient.

How to assess glomerular function and damage in humans

In human subjects, the assessment of renal function and of its changes by interventions is limited to the measurement of glomerular filtration rate (GFR), renal blood flow and the estimation of proteinuria. In humans, GFR can be determined exactly by measuring the clearance of an ideal filtration marker, such as inulin. The classic method of measuring inulin clearance in humans includes constant intravenous infusion of the compound and timed collections of urine. In order to avoid the need for timed urine collections, a number of alternative procedures have been devised. All these methods only use determinations of inulin in plasma or serum. From these, the total body inulin clearance is obtained using pharmacokinetic calculations. In order to measure total body clearance, usually called plasma clearance, inulin is either given as a constant intravenous infusion or as a bolus infusion. Both procedures overestimate GFR because of incomplete distribution of inulin during the study periods. The error may be minimized by using model-independent pharmacokinetic calculations. Unlike inulin, creatinine is not a perfect filtration marker. This is because the substance is not only eliminated by glomerular filtration but also by tubular secretion. The extent of tubular creatinine secretion is not constant in various individuals. Serum creatinine concentration is a commonly used measure of renal function in clinical practice. This parameter is determined both by the renal elimination and by the production of the compound. Differences in creatinine production among subjects and over time in a single individual may occur because of changes in muscle mass. Radioisotopic filtration markers can easily and accurately be measured in plasma and serum. Using this method, the plasma concentration-time curve of these compounds can easily be studied after intravenous bolus injection. From the plasma concentration-time curves obtained, the total body clearance (plasma clearance) of the substances can be calculated using pharmacokinetic models. Most frequently, 125l-iothalamate, 99mTc-diethylenethiaminepenta-acetic acid and 51Cr-ethylenediaminetetra-acetic acid are used for the estimation of GFR in humans. The total body clearance of all these filtration markers overestimates GFR. The error induced by this phenomenon is particularly relevant at low levels of GFR. In recent years, iohexol has been used as a filtration marker. The substance can be measured in plasma, serum and urine using high-performance liquid chromatography. So far, good agreement has been shown for GFR determined by the classic inulin clearance and by the iohexol plasma clearance. Screening for proteinuria is commonly performed using reagent test strips. Quantitative measurements of marker proteins can be used to estimate the extent and the site of damage in the nephron. These measurements may be used to estimate the progression of renal disease and the response to therapeutic interventions. Of particular interest is the degree of albuminuria which indicates nephropathy in diabetic patients and end-organ damage in patients with hypertension.