Single-void urine samples can be used to estimate quantitative microalbuminuria

The excretion of small quantities of urinary albumin (microalbuminuria) may predict renal failure in diabetes. The measurement of microalbuminuria with radioimmunoassays has been based on 24-h, overnight, and 3- to 4-h collections. To determine whether single-void urine samples can be used to estimate 24-h excretion, we compared the results of 24-h outpatient urine collections with single-void samples corrected for creatinine from diabetic and nondiabetic subjects. The overall correlation of single-void sample results expressed as microgram albumin per milligram creatinine with 24-h excretion (mg/24 h) was excellent (r = .82, P less than .001). More important, in the diabetic patients the sensitivity and specificity of detecting 24-h microalbuminuria in the abnormal range were at least 94 and 96%, respectively. Single-void urine specimens adjusted for creatinine discriminate between normal and abnormal levels of microalbuminuria, as determined in 24-h urine collection, with high specificity and sensitivity.     

Is there a physiological variability for albumin excretion rate? Study in patients with diabetes type 1 and non-diabetic individuals

BACKGROUND: To determine the intraindividual coefficient of variation (CV(i)) of albumin excretion rate (AER). METHOD: We studied 76 patients with type 1diabetes and 66 non-diabetic subjects (ND) under routine clinical conditions providing three timed overnight urine samples for urinary albumin determination by radioimmunoassay. RESULTS: Patients and ND had similar CV(i) of AER (50.7+/-33.3 vs. 58.1+/-33.2% P=0.12). Intermittent microalbuminuric subjects (one out of 3 AER >20 microg/min) had higher CV(i) of AER than normoalbuminuric and persistent microalbuminuric patients, [84.9 (37.1-145. 3) vs. 39.8 (4.9-124.8) vs. 34.6 (12.1-116.5)% P=0.0007] without difference between the two latter groups. In patients, the independent factor associated with the CV(i) of AER in multiple regression analysis was age (r(2)=0.08; P=0.01). Sensitivity (95% CL) and specificity of first AER for diagnosing microalbuminuria was 85.7% (42.0-99.2) and 91.3% (81.4-96.4). CONCLUIONS: Our findings suggest the variability of AER was physiological, unrelated to diabetic condition. First AER could be used for screening of microalbuminuria followed by a second one when the patient has AER >20 microg/min in the first. This would result in low cost for screening and diagnosis of microalbuminuria, that is not always feasible in routine clinical practice in developing countries using three urine samples.     

不同时段尿白蛋白在诊断早期糖尿病肾脏损伤中的应用

目的 研究糖尿病患者不同时段尿白蛋白(urinary albumin)的排泌情况及尿白蛋白在诊断早期糖尿病肾脏损伤中的应用.方法 收集中山医院门诊及住院糖尿病患者及健康对照组3 d内不同时间段的尿液,分析尿白蛋白天内、天间的排泌变化情况;以24 h尿白蛋白为标准判断肾脏早期损伤情况,比较不同时段尿及时间点尿与24 h尿白蛋白的相关性、诊断特异度及敏感度;评估随机尿的诊断特异度及敏感度,推导随机尿最佳诊断水平.结果尿白蛋白天间变异较大,以尿Cr和尿量分别校正后可降低变异.糖尿病组中尿白蛋白使用尿Cr校正后变异系数(CV)小于尿量校正(CV分别为49%±23%vs 64%±30%).尿白蛋白天内排泌呈节律性变化.不同尿液留取方式中夜间尿尿白蛋白/尿Cr(ratio of urinary concentrations of albumin and creatinine,ACR)与24 h尿白蛋白定量相关性最好(R~2=0.976),优于晨尿ACR(R~2=0.900)、午间餐后尿ACR(R~2=0.584)和随机尿ACR(R2=0.791).以24 h尿白蛋白总量作为判断标准进行受试者操作特性曲线(ROC曲线)分析显示,随机尿ACR的判断值为27.7 μg/mg尿Cr(存在男女性别差异:男性12.8μg/mg尿Cr vs性27.0μg/mg尿Cr).最小阴性似然比0.011时推导随机尿ACR的排除判断值为13.0 μg/mg尿Cr;最大阳性似然比481.000时推导随机尿ACR的确诊判断值为87.4 μg/mg尿Cr.结论 尿Cr较尿量能更好地降低尿白蛋白天内变异,但仍无法完全消除变异.夜尿ACR与24 h尿白蛋白定量相关性最好,可替代24 h尿白蛋白定量.随机尿ACR作为最方便留取的尿液标本亦可以较好地替代24 h尿白蛋白定量,但应考虑引入尿Cr后带来的性别间差异.以13.0 μg/mg及87.4 μg/mg作为随机尿ACR的排除判断值及确诊判断值可以便于临床医师基本排除或确定白蛋白尿的出现.     

Evaluation of a new radioimmunoassay for urinary albumin

We have evaluated a new commercially available radioimmunoassay kit for albumin determination in urine. The assay is precise; within-run precision (CV) in the clinically significant ranges is 1.8-3.5%, between-run, 1.2-8.5%. The minimum detection limit was 0.6 micrograms/ml. Analytic recovery of different concentrations of albumin added to urine ranged from 98% to 103%. Samples, stored in plastic containers, were stable at room temperature for periods up to 7 days. Mean albumin excretion rates, measured in 20 normal volunteers for 3-h and 24-h periods during the same day were similar (7.1 +/- 4.6 [SD] versus 6.5 +/- 5.0 micrograms/min). In 8 normal subjects, 3-h excretion rates measured daily for 5 days showed no significant variability. In eight insulin-dependent diabetic subjects, albumin excretion measured in short periods of urine collection (3 h) were also in close agreement with 24-h collections (24.7 +/- 28.9 versus 17.6 +/- 18 micrograms/min). From these results it appears that this commercially available kit is suitable for conveniently monitoring microalbuminuria in large numbers of patients in research studies as well as for office practice. Such widespread use should make it possible to better determine the clinical usefulness of this test in the management of diabetic patients.     

Selecting the optimum specimen for assessing slight albuminuria, and a strategy for clinical investigation: novel uses of data on biological variation

To investigate the optimum specimen for quantifying low, but abnormal, concentrations of albumin in urine, we assessed the analytical and biological components of variation in first morning, random untimed, and 24-h urine specimens from 11 apparently healthy individuals. The results were expressed in terms of albumin concentration, albumin/creatinine ratio, and albumin excretion rate. Analytical methods generally can meet the analytical goal of CV less than or equal to 18%. For reasons detailed herein, we prefer measurement of the albumin concentration in the first morning specimen. Expressing results as an albumin/creatinine ratio has little advantage. Albumin concentrations in first morning urines from 16 diabetic subjects showed larger intra-individual variation than for nondiabetic subjects but clearly fell into two groups: those with consistently normal albumin concentrations in urine and those with abnormal concentrations in some specimens. The intrinsic biological variation of the latter group means that the ideal 100% nosological specificity cannot be achieved with any cutoff point without inclusion of a large proportion of the former. Qualitative testing with a latex-agglutination technique also demonstrates this problem. Use of data on biological variation allows development of an appropriate clinical strategy to investigate diabetic patients.     

Improved competitive enzyme-linked immunoassay (ELISA) for albuminuria

Microalbuminuria has been established as a marker strongly predictive of diabetic nephropathy. The appearance of microalbuminuria (30-150 micrograms/min) is considered to herald incipient nephropathy, and the progression to clinical proteinuria (greater than 200 mg/24 h) is believed to reflect a shift from reversible to irreversible renal damage in diabetic patients. Periodic monitoring of albumin excretion could thus detect diabetic renal disease at an early, potentially reversible stage. However, this is not routinely done, largely due to cumbersome collection and methodologic constraints. We therefore have developed a simplified competitive immunoassay (ELISA) that is sensitive to 10 ng and reproducibly quantifies urinary albumin levels between 0.1-10 micrograms/ml, a range appropriate to that demarcating normal from microalbuminuric patients. Examination of results obtained with aliquots of 24 h and fractional urine collections, without and with correction for creatinine (albumin: creatine ratio), in basal and post-exercise states indicates that (a) this assay can effectively measure urine albumin concentration in single void specimens, and albumin excretion rates in fractional collections, and (b) conversion to albumin:creatinine ratio is not necessary to discriminate normal from microalbuminuric states.     

Risk factors for development of incipient and overt diabetic nephropathy in type 1 diabetic patients: a 10-year prospective observational study

OBJECTIVE: To evaluate prospectively putative risk factors for development of microalbuminuria and macroalbuminuria in type 1 diabetes. RESEARCH DESIGN AND METHODS: Prospective observational study of a cohort of type 1 diabetic patients followed in the outpatient clinic at Steno Diabetes Center for < or =10 years (median 9 years). We followed 537 patients aged > or =18 years with type 1 diabetes, with duration of diabetes > or =5 years, with normoalbuminuria (urinary albumin excretion rate < or =30 mg/24 h), and who were not taking antihypertensive medication. Risk factors for development of microalbuminuria and macroalbuminuria were evaluated. RESULTS: The mean progression of urinary albumin excretion rate was 7.6% (SE 0.8) per year. During follow-up, 134 patients (25%) progressed to persistent microalbuminuria or macroalbuminuria (>30 mg/24 h in two of three consecutive urine samples). Cox multiple regression analysis using baseline values of putative predictors of progression showed the following significant predictors of progression from normoalbuminuria to microalbuminuria or macroalbuminuria: baseline log urinary albumin excretion rate 2.63 (relative risk; 95% CI 1.65-4.19), HbA(1c) 1.13% (1.04-1.23), presence of any retinopathy 1.90 (1.26-2.88), and smoking 1.61 (1.11-2.33). Sex, duration of diabetes, arterial blood pressure, serum creatinine, height, and social class were not risk factors. CONCLUSIONS: Our study suggests that several potentially modifiable risk factors predict the development of microalbuminuria and macroalbuminuria in type 1 diabetic patients.     

Urinary albumin excretion in normal subjects and in diabetic patients measured by a radioimmunoassay: methodological and clinical aspects

We have developed a radioimmunoassay method (RIA) to measure urinary albumin excretion. We determined the albumin excretion rate (AER) (micrograms/min) of 122 healthy subjects and 145 diabetic patients (115 type I, 30 type II). The results indicate that the RIA is sensitive (0.39 +/- 0.08 mg/L), precise (CV 5-8%), and gives reliable results on previously frozen urine samples. The distribution of the AER values in healthy subjects and diabetic patients was not normal. It was normalized by log or square-root transformation of the data. Seventy-three percent of diabetic patients lay within the normal range (0.6-10.6 micrograms/min). Twenty percent could be considered "at risk" to develop overt diabetic nephropathy because their albuminuria exceeded a threshold level of 15 micrograms/min chosen previously as the cutoff value for microalbuminuria. We found no correlation between AER and glycated hemoglobin, and only a weak correlation between AER and diabetes duration in type I diabetic patients.     

Enzyme immunoassay: an improved determination of urinary albumin in diabetics with incipient nephropathy

An enzyme linked immunoadsorbent assay for urinary albumin using commercially available reagents is described. The assay range is 2.5-120 micrograms/l. When samples are analysed in two standard dilutions, the assayable albumin concentration range is 2.5-240 mg/l, covering the clinical range from normoalbuminuria to overt clinical nephropathy. Intra-assay variation was 2.1% and interassay variation 8.3%. Recovery of added albumin to urine was 95%-106% and dilution of urine was linear. The correlation to urinary albumin determined by immunodiffusion was excellent (n = 80, r = 0.99). Intraindividual variation of the 24 h urine albumin excretion of different days was high in patients with incipient diabetic nephropathy (51.5%) and was only slightly reduced by taking the variation of creatinine excretion into account (39.5%). No correlation was found between albumin excretion, and HbA1c or urine glucose excretion, indicating that minor metabolic variations are not responsible for the huge intraindividual day-to-day variations of UalbV. The study shows that more than one UalbV measurement must be done before classifying patients into groups with or without incipient diabetic nephropathy.     

Increased collagen IV excretion in diabetes. A marker of compromised filtration function

OBJECTIVE: Increased albumin excretion in diabetes is believed to be derived from hemodynamic and/or permeability abnormalities, whereas mesangial matrix expansion gives rise to the reduction in glomerular filtration surface and decline in renal function in diabetic nephropathy. We postulated that the overproduction of extracellular matrix proteins underlying glomerulosclerosis in diabetes might be associated with the excretion of increased amounts of type IV collagen in the urine. RESEARCH DESIGN AND METHODS: To explore this hypothesis, we measured the urinary excretion of (human) collagen IV by immunoassay in 65 patients with type 1 or type 2 diabetes and various degrees of albuminuria and examined its relationship to filtration function assessed by the reciprocal of the serum creatinine (RSC). RESULTS: Collagen IV excretion showed a significant (P < 0.001) inverse correlation (r = -0.62) with the RSC, and this correlation pertained regardless of whether albumin cxcretion was in the low (< or =< or = 100 microg/mg creatinine r = -0.73) or high (>100 microg/mg; r = -0.53) range. In contrast, albumin excretion showed insignificant correlation with either collagen IV excretion (r = 0.12) or with the RSC (r = -0.20). Urinary collagen IV was significantly higher (P < 0.05) in patients with an RSC value < or = 100 (28.3 +/- 2.4 ng/mg creatinine) than in patients with an RSC value > 100 (16.0 +/- 0.8 ng/mg creatinine). CONCLUSIONS: Because not all patients with microalbuminuria progress to declining renal function and some patients who develop nephropathy do not manifest albuminuria, the findings in this cross-sectional analysis suggest that measurement of urine collagen IV may be a useful noninvasive indicator to detect diabetic renal disease entering a phase of compromised renal function.     

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.     

Screening for microalbuminuria in patients with diabetes mellitus: frozen storage of urine samples decreases their albumin content

The influence of storage on urinary albumin concentration was prospectively studied with use of overnight urine specimens (Albustix negative) from 73 diabetic patients. From each urine sample four aliquots were taken. One was stored at 4 degrees C and assayed within two weeks, the other three were stored at -20 degrees C and assayed within two weeks and after two and six months. Albumin concentration was measured with laser immunonephelometry. The detection limit, 1 mg/L, suffices for the screening of diabetic patients for microalbuminuria. After storage for two and six months at -20 degrees C, significantly lower albumin concentrations were found. The difference was mainly caused by lower concentrations found in urine samples in which a precipitate had formed, which was the case in 22 and 25 samples, respectively. Thus, freezing of urine samples for determination of low concentrations of albumin may yield falsely low results. Urine samples are best stored at 4 degrees C and assayed within two weeks.     

Classification of renal proteinuria: a simple algorithm.

Total protein, albumin, alpha1-microglobulin, and immunoglobulin G (IgG) were analyzed in 1,622 urine samples without Bence-Jones proteinuria or gross hematuria. There was correlation with the histological picture obtained on renal biopsy in 61 patients. We established 24-h reference intervals for alpha1-microglobulin and IgG on 659 urine samples with total protein and albumin excretion rates below 100 mg/24 h and 30 mg/24 h, respectively, and creatinine clearance above 80 ml/min. The central 95% reference interval was found to be between 4 and 17 mg/24 h for alpha1-microglobulin and between 3 and 8.5 mg/24 h for IgG. In 80 urine samples with albumin excretion rate above 30 mg/24 h and alpha1-microglobulin and IgG within their reference intervals, we analyzed the 95% central interval of the distribution of the IgG/albumin ratios, and it was found to be within 0.01 and 0.20 (0.90 confidence interval: 0.17-0.24). Proteinuria was considered to be of the selective glomerular type if the albumin excretion rate was abnormal and the IgG/albumin ratio was under 0.20, even when the IgG excretion was within a pathological range. For the classification of proteinuria as predominantly tubular, we estimated the alpha1-microglobulin/albumin ratio in 173 urine samples with normal excretion rates of albumin and IgG and pathological excretion of alpha1-microglobulin. The discriminating value of 0.91 (0.90 confidence interval: 0.78-1.08) was accepted in order to define proteinuria of a tubular origin in the presence of a pathological albumin excretion rate. The association between albumin and IgG excretion rates and tubular reabsorption of the alpha1-microglobulin normally filtered by the glomerulus was studied in 33 urine samples from patients with no histologically significant tubulo-interstitial or vascular disease and a serum creatinine concentration below 141 pmol/l. The optimal curve-fitting function between albumin plus IgG and alpha1-microglobulin excretion rates was of the quadratic type (r = 0.927). Mixed proteinuria was considered when both, albumin and alpha1-microglobulin excretion rates were pathological and could not be included in the previously described groups.     

Development, progression, and regression of microalbuminuria in Japanese patients with type 2 diabetes under tight glycemic and blood pressure control: the Kashiwa study

OBJECTIVE: The goal of this study was to know the fate of albuminuria in Japanese patients with type 2 diabetes under tight blood pressure and glycemic control. RESEARCH DESIGN AND METHODS: Patients having normoalbuminuria (urinary albumin excretion <30 mg/g creatinine, n = 179) or microalbuminuria (albumin excretion 30-299 mg/g creatinine, n = 94) at baseline have been followed up for 8 years: ratio of men to women was 160/113, the mean age was 58 years, pretreatment HbA(1c) (A1C) was 8.8%, and blood pressure was 136/76 mmHg. A1C <6.5% and blood pressure <130/80 mmHg were targeted, and the A1C of 6.5 +/- 0.7% (mean +/- SD) and blood pressure of 127 +/- 11/72 +/- 6 mmHg have been maintained during the 8 years. Development of microalbuminuria or macroalbuminuria (albumin excretion > or =300 mg/g creatinine) in initially normoalbuminuric patients and progression to macroalbuminuria or regression to normoalbuminuria in initially microalbuminuric patients were assessed at year 8. RESULTS: Development occurred in 27 (15%) of the normoalbuminuric patients and progression and regression in 16 (17%) and 20 (21%), respectively, of the microalbuminuric patients. Significant independent relationships existed between development and higher achieved mean systolic blood pressure (SBP) and regression and lower achieved mean SBP. In the patients with achieved mean SBP <120 mmHg, development was 3%, progression was 11%, and regression was 44% during 8 years. Prediction for nephropathy by blood pressure and glycemia alone was limited. Nevertheless, albumin excretion at year 8 was positively correlated with achieved mean SBP and baseline albuminuria. CONCLUSIONS: Development and progression were low and regression was high with SBP of 120 mmHg, provided A1C was maintained at 6.5%.     

2型糖尿病患者微量白蛋白尿临界值的研究

目的研究2型糖尿病(T2DM)患者晨尿、随机尿的尿白蛋白/肌酐比值(ACR)及尿白蛋白(U-Alb)浓度,判定微量白蛋白尿的临界值,以检测早期糖尿病肾脏疾病(DKD)。方法收集169例T2DM患者及40名健康体检者(正常对照组)的24 h尿、晨尿、随机尿,以24 h尿白蛋白排泄率(UAE)为早期DKD的判定标准,分析目前临床应用的晨尿、随机尿的ACR及U-Alb浓度判定微量白蛋白尿的临界值对早期DKD的筛查效能;根据受试者工作特征(ROC)曲线分析,Youden指数最大时对应的晨尿、随机尿的ACR及U-Alb浓度为检测早期DKD微量白蛋白尿的临界值。结果在微量白蛋白尿判定结果中,晨尿ACR与24 h UAE的符合率为43%,UAlb为37%;随机尿ACR为48%,U-Alb为41%,以上4个指标与24 h UAE的判定结果有明显差异(P均0.001)。正常对照组晨尿、随机尿检测结果判定与24 h UAE一致,均为正常。ROC曲线分析显示ACR晨尿临界值为男16 mg/g、女23 mg/g(Youden指数分别为0.70、0.67,阴性预测值分别为97%、100%,阳性预测值分别为72%、65%);ACR随机尿临界值为男17 mg/g、女28 mg/g(Youden指数分别为0.68、0.67,阴性预测值分别为90%、90%,阳性预测值分别为61%、82%);U-Alb晨尿临界值为男16 mg/L、女15 mg/L(Youden指数分别为0.57、0.59,阴性预测值分别为84%、87%,阳性预测值分别为90%、73%);U-Alb随机尿临界值为男17 mg/L、女14 mg/L(Youden指数分别为0.56、0.53,阴性预测值分别为73%、81%,阳性预测值分别为85%、71%)。ACR的最大Youden指数均0.6,且高于相应的U-Alb浓度的Youden指数。结论目前临床应用的晨尿、随机尿微量白蛋白尿的临界值判定T2DM患者早期肾病的漏诊率较高,应重新建立T2DM患者晨尿、随机尿ACR及U-Alb的临界值,以利于DKD的早期防治。     

不同时段尿微量清蛋白对糖尿病早期肾损害的诊断价值

目的探讨2型糖尿病肾病患者不同时段尿微量清蛋白(u-MA)变化及其对2型糖尿病患者早期肾损伤的诊断价值。方法收集糖尿病肾病患者组(n=27)和健康对照组(n=30)连续3 d的晨尿、餐后尿、随机尿和24 h尿,进行尿微量清蛋白测定。结果糖尿病患者尿微量清蛋白排泌高峰为餐后尿(61.7±26.5 mg/L),其次为晨尿(58.9±23.5 mg/L)和24 h尿(56.6±13.2 mg/L),3者显著高于随机尿(37.2±21.4 mg/L)(P<0.05),且各时段尿微量清蛋白都有较大的日间差异,以随机尿差异最大CV=57.5%,餐后尿、晨尿、和24 h尿分别为42.9%、39.9%和23.3%,糖尿病肾病患者各时段尿微量清蛋白与对照组比较差异有统计学意义(P<0.05)。结论餐后尿和晨尿微量清蛋白含量的多次检测有利于提高2型糖尿病患者早期肾损害的诊断。     

Screening for microalbuminuria. A comparison of single sample methods of collection and techniques of albumin analysis.

OBJECTIVE--To evaluate single-sample urine collections to determine their ability to screen patients for the presence of microalbuminuria. Microalbuminuria in patients with type I diabetes predicts the development of diabetic renal disease. RESEARCH DESIGN AND METHODS--Cross-sectional analysis of single-sample urine collection techniques (first morning void, random upright void) and methods of albumin analysis (RIA, reagent tablet) were compared with conventional 24-h urine collections (RIA). The study included 94 patients (45 males, 49 females; mean serum creatinine 88 microM) with type I diabetes, selected from a screened population of 301 patients from the University Hospital Subspecialty Clinics. RESULTS--A 24-hour urine collection RIA analysis for albumin revealed 36 normal patients (< 30 mg), 27 with microalbuminuria (30-300 mg), and 31 with albuminuria (> 300 mg). Random upright urine samples were more sensitive (RIA 89%, tablets 78%) for the detection of microalbuminuria than first morning void specimens (RIA 70%, tablets 60%). Specificity was > 80% with both random and first morning voids. CONCLUSIONS--Screening for microalbuminuria can be performed in the clinic by random upright single-sample urine collections. When reagent tablets were used, these results are available immediately. Patients who screen positive should be confirmed by 24-h or other timed urine collections.     

Decreases in albumin/creatinine and N-acetylglucosaminidase/creatinine ratios in urine samples stored at -20 degrees C.

The effects of storage for 6 months or 2 years at -20 degrees C were studied in urine samples from Type II diabetic patients by assaying albumin by immunoturbidity, N-acetylglucosaminidase (EC 3.2.1.30) by methoxynitrovinylphenol release, and creatinine by the Jaffé method. There were significant decreases (P < 0.001) in albumin/creatinine ratios from 1.14 (0.63-2.98) to 0.83 (0.32-2.12) g/mol (median + interquartile ranges) after 6 months (n = 97), and from 1.64 (0.74-5.72) to 1.00 (0.37-4.54) g/mol after 2 years (n = 89). The percentage of samples with results below the detection limit of the albumin assay (2 mg/L) increased from 5% to 21% after 6 months and from 0% to 34% after 2 years. N-Acetylglucosaminidase/creatinine ratios decreased (P < 0.001) from 520 (358-832) to 380 (263-695) U/mol after 6 months and from 520 (330-865) to 258 (82-462) U/mol after 2 years. The effect of storage was greater in samples with concentrations in the normal range (< 2.5 g/mol for albumin/creatinine, < 500 U/mol for N-acetylglucosaminidase/creatinine). Samples with albumin concentrations more than twice the normal range were still detected as abnormal after storage at -20 degrees C; e.g., 18% were > 5 g/mol (albumin/creatinine) initially, with 17% > 5 g/mol after 6 months of storage. We therefore recommend storage of urine samples at 4 degrees C for no longer than 7 days before assay.     

Urinary albumin excretion in healthy adult subjects: reference values and some factors affecting their interpretation

A conventional radioimmunoassay has been used to measure urinary albumin concentration in overnight, recumbent and daytime, ambulant samples from 127 healthy, normotensive volunteers (mean age 33.3 yr SD 12.4; 59 males, 68 females). Reference values were obtained for urine albumin concentration (mg/l), albumin/creatinine ratio (mg/mmol), and albumin excretion rate (microgram/min). The frequency distributions of these variables were positively skewed, but became Gaussian on logarithmic transformation of the data. Albumin excretion was significantly higher in daytime, ambulant samples than in overnight, recumbent samples (p less than 0.001). Surface area was not correlated with urine albumin concentration but it was negatively correlated with urine albumin/creatinine ratio (p less than 0.05) due to the association between surface area and creatinine excretion. Urine albumin concentration was negatively correlated with age, but this was due to a higher urine flow rate in older subjects. There was no significant association with sex or with mean arterial blood pressure in the normal range. Two repeated measurements showed that variability was high and comparable for urine albumin concentration, albumin/creatinine ratio and albumin excretion rate: it was not significantly less in overnight, recumbent than in day-time, ambulant samples.     

Non-diabetic microalbuminuria in clinical practice and its relationship to posture, exercise and blood pressure.

1. The effects of posture and exercise on the relationship between low-level urinary albumin excretion (microalbuminuria) and blood pressure was investigated in two groups of non-diabetic patients at increased cardiovascular risk: 21 otherwise healthy patients with untreated essential hypertension (blood pressure greater than 160/90 mmHg), and 14 age-matched patients with blood pressure at presentation within the normotensive range (less than 160/90 mmHg) attending a cardiovascular clinic for assessment of chest pain. 2. A significant linear relationship between logarithmically transformed 'spot' urinary albumin/creatinine ratio and simultaneous clinic blood pressure existed when data from both groups of patients were analysed (r = 0.58, P less than 0.05). The relationship between the scatter plot of blood pressure and the albumin/creatinine ratio appeared most marked when the mean blood pressure exceeded 120 mmHg. 3. In patients with essential hypertension, clinic systolic blood pressure was related to the albumin/creatinine ratio in simultaneous 'spot' urine samples (r = 0.69, P less than 0.05) and also to the albumin/creatinine ratio in early-morning urine samples (r = 0.51, P less than 0.05). However, the relationship between clinic blood pressure and simultaneous 'spot' urinary albumin/creatinine ratio in the patients with chest pain did not achieve significance when analysed independently. 4. Hourly averaged ambulatory intra-arterial blood pressure was recorded in four of the patients with essential hypertension during normal daytime activity, and a significant correlation with the simultaneous hourly daytime urinary albumin/creatinine ratio was found (r = 0.65, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)