Microalbuminuria: an important diagnostic tool

Urinary N-acetyl-beta-d-glucosaminidase levels in diabetic adults

Diabetes mellitus (DM) is known to be one of the most common causes of end-stage renal disease. The disease is usually not detected on time, because of the large functioning reserve of the kidney. Currently used markers (serum creatinine, creatinine clearance, urea, and electrolytes) remain relatively normal even when more than 50% of the renal nephron is not functioning. The aim of this study was to determine the level of urinary N-acetyl-beta-d-glucosaminidase (NAG) in diabetic adults in comparison with some currently used markers. A total of 56 diabetic patients between the ages of 23 and 63 were used for this study and 30 nondiabetic between the ages of 18 and 62 were used as control. The diabetic patients were classified into three groups based on how long they have been diagnosed: <2 years (25), 2–5 years (30), and >5 years (25). Spot midstream urine samples were collected into sterile containers, and blood samples were collected into plain tubes. All the analyses were done spectrophotometrically. Creatinine clearance was calculated using the Cockcroft–Gault Equation. There was a significant increase (P < 0.01) in NAG values of 2–5 years and above 5 years and control. The urinary microalbumin concentration of controls was significantly different (P < 0.05) only with those who have had DM for <2 years. Urinary creatinine concentration of control was significantly higher (P < 0.05) than values of all the diabetic groups. There was a significant increase (P < 0.01) in creatinine clearance of control group and those who have had DM for <2 years. It is thus concluded that urinary NAG can be used as an early marker in the diagnosis of diabetic nephropathy since urinary NAG increases first before the other markers analyzed in this current study begins to increase.

A Study of Microalbuminuria (MAU) and Advanced Glycation End Products (AGEs) Levels in Diabetic and Hypertensive Subjects

The prevalence of non-communicable diseases like diabetes mellitus (DM) and hypertension (HTN) is growing worldwide. Both lead to nephropathy if not controlled effectively. Microalbuminuria (MAU) is recognized as an early predictor for nephropathy. Additionally, the timely detection of advanced glycation end products (AGEs) is also considered to be an important prognostic factor for diabetic nephropathies. Hence, screening for the early detection of MAU and AGEs would be an useful and relatively inexpensive laboratory test for early clinical diagnosis for the incidence of nephropathy in these diseases. This study was conducted in DM, HTN and pregnancy induced hypertensive (PIH) subjects. MAU and N^ε-Carboxymethyllysine (CML) levels were estimated by in-house RIA kits in the patient groups and controls, while the total AGEs level in serum was determined by ELISA. The levels of MAU, CML and AGE-BSA were observed to be significantly higher in DM, HTN and PIH subjects compared to controls (p < 0.001). Increased serum CML and AGEs levels in DM, HTN and PIH subjects indicated ongoing glycemic damage and their susceptibility to develop renal complications.

Nocturnal blood pressure fall as predictor of diabetic nephropathy in hypertensive patients with type 2 diabetes

BACKGROUND

Hypertensive patients with reduced blood pressure fall (BPF) at night are at higher risk of cardiovascular events (CVE).

METHODS

We evaluated in hypertensive diabetic patients, if a reduced nocturnal BPF can precedes the development of diabetic nephropathy (DN). We followed 70 patients with normal urinary albumin excretion (UAE) for two years. We performed 24-hours ambulatory BP monitoring in baseline and at the end of the study.

RESULTS

Fourteen (20%) patients (GI) developed DN (N = 11) and/or CVE (n = 4). Compared to the remaining 56 patients (GII) in baseline, GI had similar diurnal systolic (SBP) and diastolic BP (DBP), but higher nocturnal SBP (138 +/- 15 vs 129 +/- 16 mmHg; p < 0.05) and DBP (83 +/- 12 vs 75 +/- 11 mmHg; p < 0,05). Basal nocturnal SBP correlated with occurrence of DN and CVE (R = 0.26; P < 0.05) and with UAE at the end of the study (r = 0.3; p < 0.05). Basal BPF (%) correlated with final UAE (r = -0.31; p < 0.05). In patients who developed DN, reductions occurred in nocturnal systolic BPF (12 +/- 5 vs 3 +/- 6%, p < 0,01) and diastolic BPF (15 +/- 8 vs 4 +/- 10%, p < 0,01) while no changes were observed in diurnal SBP (153 +/- 17 vs 156 +/- 16 mmHg, NS) and DBP (91 +/- 9 vs 90 +/- 7 mmHg, NS). Patients with final UAE < 20 microg/min, had no changes in nocturnal and diurnal BP.

CONCLUSIONS

Our results suggests that elevations in nocturnal BP precedes DN and increases the risk to develop CVE in hypertensive patients with T2DM.

Why to screen heart disease in diabetes

The expanding diabetic epidemic and the high risk of cardiovascular events in diabetic patients suggest that screening heart disease in this population is an important issue. Nonetheless, the advisability of large-scale screening in asymptomatic individuals with diabetes is debated, because available techniques are expensive and have suboptimal diagnostic accuracy. Moreover, all diabetic patients should be treated aggressively as if they all had a positive screening test, because diabetes could be considered a coronary risk equivalent. In this article, we underline the importance of an early diagnosis of coronary artery disease and heart failure in diabetic patients, suggesting that positive screening tests have significant implications in clinical management.

Combination of the electrocardiographic strain pattern and albuminuria for the prediction of new-onset heart failure in hypertensive patients: the LIFE study

BACKGROUND

Although albuminuria and the electrocardiographic (ECG) strain pattern each predict development of heart failure (HF), whether combining albuminuria and strain improves prediction of new HF is unclear.

METHODS

The relation of ECG strain and albuminuria to new-onset HF was examined in 7,786 hypertensive patients with no history of HF, who were randomly assigned to treatment with losartan or atenolol. Albuminuria was defined by a urine albumin/creatinine ratio >30.94 mg/g.

RESULTS

During a mean follow-up of 4.7 +/- 1.1 years, new-onset HF occurred in 231 patients (3.0%). Five-year HF rate was highest when both strain and albuminuria were present (10.4%), intermediate when only ECG strain (8.0%) or albuminuria (4.9%) was present, and lowest when neither strain nor albuminuria was present at baseline (1.8%, P < 0.0001). In Cox multivariable analyses, controlling for HF risk factors, treatment assignment and baseline severity of ECG left ventricular hypertrophy (LVH) by both Sokolow-Lyon voltage and Cornell product, ECG strain and albuminuria remained significant predictors of incident HF, with the presence of both strain and albuminuria associated with the highest risk (HR 2.8, 95% CI 1.8-4.4) and the presence of only strain (HR 2.6, 95% CI 1.7-4.0) or albuminuria (HR 2.1, 95% CI 1.5-2.8) with intermediate risk of new HF compared with the absence of both strain and albuminuria.

CONCLUSIONS

The combination of albuminuria and ECG strain identifies hypertensive patients at an increased risk of developing HF in the setting of aggressive blood pressure lowering, independent of treatment modality and of other risk factors for HF.

Reductions in albuminuria and in electrocardiographic left ventricular hypertrophy independently improve prognosis in hypertension: the LIFE study

BACKGROUND

In the Losartan Intervention For Endpoint reduction in hypertension (LIFE) study, reduced urine albumin/creatinine ratio (UACR) as well as regression of left ventricular hypertrophy have been associated with lower incidence of cardiovascular events. We wanted to investigate whether these prognostic improvements were independent.

METHODS

In 6679 hypertensive patients included in the LIFE study, we measured UACR, left ventricular hypertrophy by electrocardiography, serum cholesterol, plasma glucose and blood pressure after 2 weeks of placebo treatment and again after 1 year of anti-hypertensive treatment with either an atenolol- or a losartan-based regimen. During this first year of treatment, 77 patients encountered a non-fatal stroke or myocardial infarction and were excluded to avoid bias. During the next 3-4 years, 610 composite endpoints [cardiovascular death (n = 228), fatal or non-fatal myocardial infarction or stroke] were recorded.

RESULTS

In Cox regression analyses, the composite endpoint was after adjustment for treatment allocation predicted by baseline logUACR [hazard ratio (HR) = 1.16 per 10-fold increase, P < 0.05], 1-year logUACR (HR = 1.29 per 10-fold increase), baseline Sokolow-Lyon voltage (HR = 1.01 per mm, both P < 0.001) and 1-year Cornell product (HR = 1.01 per 100 mm x ms, P < 0.01). Cardiovascular death was predicted by 1-year logUACR (HR = 1.59, P < 0.001), baseline Sokolow-Lyon voltage (HR = 1.01, P = 0.06) and 1-year Cornell product (HR = 1.02, P < 0.001). Both were predicted independent of age, Framingham risk score, current smoking, history of cardiovascular disease and diabetes. Gender, serum cholesterol, plasma glucose and blood pressure did not enter the models.

CONCLUSIONS

Baseline UACR and Sokolow-Lyon voltage, as well as in-treatment UACR and Cornell product, added to the risk prediction independent of traditional risk factors, indicating that albuminuria and left ventricular hypertrophy reflect different aspects of cardiovascular damage and are modifiable cardiovascular risk factors.

Albuminuria predicts cardiovascular events independently of left ventricular mass in hypertension: a LIFE substudy

We wanted to investigate whether urine albumin/creatinine ratio (UACR) and left ventricular (LV) mass, both being associated with diabetes and increased blood pressure, predicted cardiovascular events in patients with hypertension independently. After 2 weeks of placebo treatment, clinical, laboratory and echocardiographic variables were assessed in 960 hypertensive patients from the LIFE Echo substudy with electrocardiographic LV hypertrophy. Morning urine albumin and creatinine were measured to calculate UACR. The patients were followed for 60+/-4 months and the composite end point (CEP) of cardiovascular (CV) death, nonfatal stroke or nonfatal myocardial infarction was recorded. The incidence of CEP increased with increasing LV mass (below the lower quartile of 194 g to above the upper quartile of 263 g) in patients with UACR below (6.7, 5.0, 9.1%) and above the median value of 1.406 mg/mmol (9.7, 17.0, 19.0%(***)). Also the incidence of CV death increased with LV mass in patients with UACR below (0, 1.4, 1.3%) and above 1.406 mg/mmol (2.2, 6.4, 8.0%(**)). The incidence of CEP was predicted by logUACR (hazard ratio (HR)=1.44(**) for every 10-fold increase in UACR) after adjustment for Framingham risk score (HR=1.05(***)), history of peripheral vascular disease (HR=2.3(*)) and cerebrovascular disease (HR=2.1(*)). LV mass did not enter the model. LogUACR predicted CV death (HR=2.4(**)) independently of LV mass (HR=1.01(*) per gram) after adjustment for Framingham risk score (HR=1.05(*)), history of diabetes mellitus (HR=2.4(*)) and cerebrovascular disease (HR=3.2(*)). (*)P<0.05, (**)P<0.01, (***)P<0.001. In conclusion, UACR predicted CEP and CV death independently of LV mass. CV death was predicted by UACR and LV mass in an additive manner after adjustment for Framingham risk score and history of CV disease.

A blood pressure independent association between glomerular albumin leakage and electrocardiographic left ventricular hypertrophy. The LIFE Study. Losartan Intervention For Endpoint reduction

In the Losartan Intervention For Endpoint reduction (LIFE) study left ventricular (LV) hypertrophy was associated with increased urine albumin/creatinine ratio (UACR) at baseline. To evaluate whether this association was due only to parallel blood pressure (BP)-induced changes we re-examined the patients after 1 year of antihypertensive treatment to investigate whether changes in LV hypertrophy and UACR were related independently of changes in BP. In 7,142 hypertensive patients included in the LIFE study, we measured UACR, LV hypertrophy by electrocardiography, plasma glucose and BP after 2 weeks of placebo treatment and again after 1 year of antihypertensive treatment with either an atenolol or a losartan based regime. At baseline and still after 1 year of treatment logUACR (R = 0.28, P < 0.001) was still correlated to LV hypertrophy (beta = 0.05) assessed by ECG independently of systolic BP (beta = 0.16), plasma glucose (beta = 0.19) and age (beta = 0.08). Change in logUACR (R = 0.19, P < 0.001) during treatment was correlated to change in LV hypertrophy (beta = 0.10) independently of reduction in systolic BP (beta = 0.13) and change in plasma glucose (beta = 0.06). After 1 year of antihypertensive treatment UACR was still related to LV hypertrophy independently of systolic BP, and the reduction in UACR during that first year of treatment was related to regression of LV hypertrophy independently of reduction in systolic BP. This suggests that the relationship between LV hypertrophy and glomerular albumin leakage is not just due to parallel BP-induced changes. As glomerular albumin leakage may represent generalised vascular damage we hypothesise a vascular relationship between cardiac and glomerular damage.

Comparison of methods for urinary albumin determination in patients with type 1 diabetes

We tested the correlation of the albumin-to-creatinine ratio (A/C) in an early-morning urine sample, measured with a commercial kit (DCA 2000), with the conventional immunoturbidimetric determination in the laboratory and with overnight albumin excretion rate (reference method). Fifty-five type 1 diabetic adolescents had their first-morning urine collected on the 1st and 8th day of the period. Urinary albumin and creatinine were determined immediately using the DCA 2000 kit. Samples were also stored for laboratory analysis. To evaluate the correlation between early-morning urinary A/C ratio and overnight albumin excretion rate, 16 subjects had a timed overnight urine collection. A/C ratios determined with the DCA 2000 kit and by the laboratory method were 13.1 +/- 20.5 and 20.4 +/- 46.3 mg/g, respectively. A/C results by both methods proved to be strongly correlated (r = 0.98, P<0.001). DCA 2000-determined A/C showed 50% sensitivity and 100% specificity when compared to the reference method. Spot urinary A/C of the subset of 16 subjects significantly correlated with their overnight albumin excretion rate (r = 0.98, P<0.001). Intraindividual variation ranged from 17 to 32% and from 9 to 63% for A/C and overnight albumin excretion rate, respectively. In conclusion, an early-morning specimen should be used instead of timed overnight urine and the A/C ratio is an accurate, reliable and easily determined parameter for the screening of diabetic nephropathy. Immediate measurement of the A/C ratio is feasible using the DCA 2000 kit. Intraindividual variability indicates the need for repeated determinations to confirm microalbuminuria and the diagnosis of incipient diabetic nephropathy.

Microalbuminuria in hypertensive patients with electrocardiographic left ventricular hypertrophy: the LIFE study

OBJECTIVES

Left ventricular hypertrophy and albuminuria have both been shown to predict increased cardiovascular morbidity and mortality. However, the relationship between these markers of cardiac and renal glomerular damage has not been evaluated in a large hypertensive population with target organ damage. The present study was undertaken to determine whether albuminuria is associated with persistent electrocardiographic (ECG) left ventricular hypertrophy, independent of established risk factors for cardiac hypertrophy, in a large hypertensive population with left ventricular hypertrophy who were free of overt renal failure.

METHODS

Patients with stage II-III hypertension were enrolled in the study if they had left ventricular hypertrophy on a screening ECG by Cornell voltage-duration product and/or Sokolow-Lyon voltage criteria, and clinic blood pressures between 160 and 200/95-115 mmHg and plasma creatinine < 160 mmol/l. A second ECG and morning spot urine were obtained after 14 days of placebo treatment. Renal glomerular permeability was evaluated by urine albumin/creatinine (UACR, mg/mmol). Microalbuminuria was present if UACR > 3.5 mg/mmol and macroalbuminuria if UACR > 35 mg/mmol.

RESULTS

The mean age of the 8029 patients was 66 years, 54% were women. Microalbuminuria was found in 23% and macroalbuminuria in 4% of patients. Microalbuminuria was more prevalent in patients of African American (35%), Hispanic (37%) and Asian (36%) ethnicity, heavy smokers (32%), diabetics (36%) and in patients with ECG left ventricular hypertrophy by both ECG-criteria (29%). Urine albumin/creatinine was positively related to Sokolow-Lyon voltage criteria and Cornell voltage-duration product criteria. In multiple regression analysis, higher UACR was independently associated with older age, diabetes, higher blood pressure, serum creatinine, smoking and left ventricular hypertrophy. Patients smoking > 20 cigarettes/day had a 1.6-fold higher prevalence of microalbuminuria and a 3.7-fold higher prevalence of macroalbuminuria than never-smokers. ECG left ventricular hypertrophy by Cornell voltage-duration product or Sokolow-Lyon criteria was associated with a 1.6-fold increased prevalence of microalbuminuria and a 2.6-fold increase risk of macroalbuminuria compared to no left ventricular hypertrophy on the second ECG.

CONCLUSIONS

In patients with moderately severe hypertension, left ventricular hypertrophy on two consecutive ECGs is associated with increased prevalences of micro- and macroalbuminuria compared to patients without persistent ECG left ventricular hypertrophy. High albumin excretion was related to left ventricular hypertrophy independent of age, blood pressure, diabetes, race, serum creatinine or smoking, suggesting parallel cardiac damage and albuminuria.

Urine albumin/creatinine ratio and echocardiographic left ventricular structure and function in hypertensive patients with electrocardiographic left ventricular hypertrophy: the LIFE study. Losartan Intervention for Endpoint Reduction

BACKGROUND

Albuminuria, reflecting systemic microvascular damage, and left ventricular (LV) geometric abnormalities have both been shown to predict increased cardiovascular morbidity and mortality. However, the relationship between these markers of cardiovascular damage has not been evaluated in a large hypertensive population.

METHODS

The urine albumin/creatinine ratio (UACR) and echocardiographic measures of LV structure and function were obtained in 833 patients with stage I to III hypertension and LV hypertrophy determined by electrocardiogram (ECG) (Cornell voltage-duration or Sokolow-Lyon voltage criteria) after 14 days of placebo treatment.

RESULTS

Patients' mean ages were 66 years, 42% were women, 23% had microalbuminuria, and 5% had macroalbuminuria. Patients with eccentric or concentric LV hypertrophy had higher prevalences of microalbuminuria (average 26%-30% vs 9%, P <.001) and macroalbuminuria (6%-7% vs <1%, P <.001). Furthermore, patients with microalbuminuria and macroalbuminuria had a significantly higher LV mass and lower endocardial and midwall fractional shortening. Patients with abnormal diastolic LV filling parameters had a significantly increased prevalence of microalbuminuria. In univariate analyses, UACR correlated positively to LV mass, systolic blood pressure, age (all P <.001) and pulse pressure/stroke volume and negatively to relative wall thickness (both P <.01) and endocardial (P <.05) and midwall shortening (P <.001) but not to diastolic filling parameters. In multiple regression analysis higher UACR was associated with higher LV mass (beta=.169, P <.001) independently of older age (beta =.095, P <.01), higher systolic pressure (beta=.163), black race (beta=.186), and diabetes (beta=.241, all P <.001).

CONCLUSIONS

In hypertensive patients with ECG LV hypertrophy, abnormal LV geometry and high LV mass are associated with high UACR independent of age, systolic blood pressure, diabetes, and race, suggesting parallel cardiac and microvascular damage.

Normal values of overnight albumin excretion rate in a sample of healthy Italian children and adolescents

The aim of this study was to define normal values of albumin excretion rate (AER) in young people. We measured overnight timed AER (tAER, microgram/min) by a double-antibody radioimmunoassay in 281 healthy Italian children and adolescents (160 M and 121 F), aged 7-19 years. The frequency distribution of tAER deviated from normality, therefore percentiles were used: median and 95th percentile were 2.3 and 6.9 micrograms/min respectively. Log transformed tAER was not related to age or pubertal stage. "Borderline" AER refers to AER higher than normal 95th percentile in non-diabetic subjects but lower than microalbuminuria threshold level. Incipient nephropathy, expressed as "borderline" AER, has been reported in adult IDDM patients, and can be reversed by improving metabolic control. Because incipient diabetic nephropathy may be present in young IDDM patients without microalbuminuria, screening for AER should be recommended for pediatric diabetic patients, also before puberty, in order to detect early renal damage and the "borderline" AER state.

Ambulatory blood pressure and urinary albumin excretion in clinically healthy subjects

A slightly elevated urinary albumin excretion rate (UAER) is a predictor of atherosclerotic cardiovascular disease. The mechanism is unknown, but moderate office blood pressure elevation has been demonstrated as part of a clustering of known atherosclerotic risk factors in subjects with elevated UAER. Because 24-hour ambulatory blood pressure is a superior predictor of hypertensive target organ involvement, we aimed to investigate blood pressure profile in clinically healthy subjects with elevated UAER. Ambulatory blood pressure monitoring was performed with a portable recorder in 27 subjects with an elevated UAER (>6.6 microg/min, overnight urine collection) and 46 normoalbuminuric control subjects. Mean+/-SD systolic and diastolic ambulatory blood pressures (24-hour) were significantly higher in subjects with elevated UAER than in normoalbuminuric controls (134+/-12 versus 128+/-11 mm Hg and 78+/-7 versus 75+/-6 mm Hg, P<0.05), as were systolic and diastolic blood pressure loads [median (range): 42% (6 to 94%) versus 23% (1 to 89%) and 20% (0 to 68%) versus 6% (0 to 62%), P<0.05]. The circadian variation of blood pressure was normal in subjects with elevated UAER. However, the increased urinary loss of albumin could not be solely related to the higher blood pressure. In conclusion, apparently healthy subjects with elevated UAER had slightly but significantly higher 24-hour systolic and diastolic blood pressure levels in addition to increased blood pressure loads but normal circadian variation. The demonstrated differences in blood pressure may offer a partial explanation for the association between elevated urinary albumin excretion and atherosclerotic cardiovascular risk.

Prevalence and epidemiology of micro- and macroalbuminuria in Ethiopian diabetic patients

A cross-sectional study was conducted on the prevalence and epidemiology of micro- and macroalbuminuria in diabetic outpatients in Gondar, Ethiopia. Microalbuminuria was defined as a mean urinary albumin concentration of 30-299mg L-1 in morning urine of three consecutive visits. The frequency of micro- and macroalbuminuria was 32% and 15% in IDDM patients and 37% and 20% in NIDDM patients, respectively. When only patients with a duration of more than 5 years were considered, micro- and macroalbuminuria were prevalent in 33% and 23% of IDDM, and 36% and 31% of NIDDM patients, respectively. In multiple regression analysis, urinary albumin levels (log) were significantly associated with systolic blood pressure and duration in IDDM patients even when proteinuric patients were excluded from the analysis. In NIDDM patients duration and diastolic blood pressure were significant predictors of urinary albumin concentrations. In order to delay chronic complications, screening for microalbuminuria by stick-testing in urine should be introduced into routine laboratory practice in developing countries.

Microalbuminuria in type II diabetes

OBJECTIVE

To emphasize the prognostic significance of microalbuminuria in patients with type II diabetes and to summarize interventional studies in patients with non-insulin-dependent diabetes mellitus and nephropathy.

METHODS

The definition of microalbuminuria is reviewed, the implications of its presence are discussed, and published trials of medical intervention to treat proteinuria in patients with type II diabetes are outlined.

RESULTS

Microalbuminuria--defined as the presence of 30 to 300 mg of protein in a 24-hour urine specimen or a urinary albumin excretion rate of 20 to 200 mg/min--is frequently present in patients with non-insulin-dependent diabetes mellitus. It has been shown to be an independent cardiovascular risk factor as well as a predictor for the eventual development of renal failure. Intervention trials indicate that treatment with "tight" blood glucose control and antihypertensive agents, especially angiotensin-converting enzyme inhibitors, may be beneficial in reversing early proteinuria or at least in preventing the progression to renal failure.

CONCLUSION

The presence of microalbuminuria in patients with type II diabetes mellitus is associated with premature death from cardiovascular disease and the development of renal failure. Thus, aggressive therapy should be instituted.