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

Increased blood pressure and erythrocyte sodium/lithium countertransport activity are not inherited in diabetic nephropathy

Genetic predisposition to essential hypertension, represented by maximal erythrocyte sodium/lithium countertransport activity, has been suggested as a marker for the risk of developing clinical nephropathy in Type 1 (insulin-dependent) diabetes mellitus. To evaluate this hypothesis we measured arterial blood pressure and maximal sodium/lithium countertransport activity of erythrocytes in 80 parents of 49 Type 1 diabetic patients with clinical nephropathy, 78 parents of 49 normoalbuminuric patients and 17 age-matched non-diabetic individuals. The two diabetic groups were carefully matched. In the two groups of parents blood pressure and cell sodium/lithium countertransport activity showed no significant differences (137/83 vs 133/81 mm Hg and 0.33 vs 0.32 mmol/(1 cells x h) respectively). The proportion of parents who had died or received antihypertensive drugs was similar in the two groups. The patients with Type 1 diabetes had significantly higher sodium/lithium countertransport compared to the 39 non-diabetic control subjects independently of the presence or absence of nephropathy (p less than 0.002). However, patients with nephropathy tended to have higher sodium/lithium countertransport activity than normoalbuminuric patients (0.48 vs 0.41 mmol/(1 cells x h), p = 0.06). We conclude that genetic predispositions to essential hypertension and increased maximal erythrocyte sodium/lithium countertransport activity do not appear to be risk markers for the development of clinical nephropathy in Type 1 diabetic patients.

Relationship between nephropathy, retinopathy, and autonomic neuropathy in patients with type I diabetes

Seventy-two Type I diabetic patients were divided into three groups according to 24 hour urinary albumin excretion (UalbV, mean of three urine collections): normoalbuminuric group 1 (n = 49, UalbV less than or equal to 26 mg/24 h), microalbuminuric group 2 (n = 16, 26 less than UalbV less than or equal to 250 mg/24 h), proteinuric group 3 (n = 7, UalbV greater than 250 mg/24 h). Fluorescein angiography and three cardiovascular autonomic tests were performed. Relative frequencies of ocular findings (no retinopathy/simplex retinopathy/preproliferative and proliferative retinopathy) were determined in each group: group 1 (0.31/0.63/0.06), group 2 (0.56/0.38/0.06), and group 3 (0/0.43/0.57). The most severely affected autonomic function was observed in group 3 (p less than 0.01 vs. group 1). Significant partial correlations were found between UalbV and retinopathy (p less than 0.01), UalbV, and autonomic neuropathy (p less than 0.05), retinopathy and autonomic neuropathy (p less than 0.01), and blood pressure and UalbV and/or autonomic neuropathy (p less than 0.01). No correlation was found between the variables and the previous 15 months' metabolic control. The results suggest that nephropathy, retinopathy, and autonomic neuropathy are signs of a generalized diabetic microangiopathic process whose progression may be influenced by factors other than diabetes duration and metabolic control.

Prevalence of hypertension in type 1 (insulin-dependent) diabetes mellitus

The prevalence of hypertension in a representative sample (n = 10202) of the Danish general population aged 16-59 years was assessed to 4.4% based on three blood pressure readings. In Type 1 (insulin-dependent) diabetic patients of similar age (n = 1703) the prevalence was determined in a similar way to 14.7% (p less than 0.00001). The excess prevalence in Type 1 diabetic patients was due to hypertension in patients with incipient and clinical nephropathy as the prevalence of hypertension among diabetic patients with normal urinary albumin excretion (essential hypertension) was 3.9%, similar to that observed in the general population. The patients with Type 1 diabetes and essential hypertension had higher systolic (146 +/- 19 vs 133 +/- 18 mm Hg, p less than 0.00001) and diastolic blood pressure (87 +/- 12 vs 79 +/- 7 mm Hg, p less than 0.00001), but less changes in the eye background than patients with incipient nephropathy (urinary albumin excretion 30-300 mg/24 h) (p less than 0.03), indicating that the two groups were also different with respect to other microangiopathic lesions. Patients with essential hypertension were defined as having a normal urinary albumin excretion before and during antihypertensive treatment (if any). They were followed-up for a 58 (6-234) month period. We confirmed that hypertension is more common among Type 1 diabetic patients than in the general population and found the prevalence of essential hypertension similar in Type 1 diabetic patients to the non-diabetic population. This supports our hypothesis that hypertension is very unlikely to be the cause of diabetic nephropathy.

Nephrotoxicity of cyclosporin A in patients with newly diagnosed type 1 diabetes mellitus

Renal function was studied in 18 patients with Type 1 diabetes mellitus. All were participating in the Canadian-European randomized placebo-controlled cyclosporin trial in newly diagnosed Type 1 diabetic patients, nine being randomized to placebo, and nine to cyclosporin A. During treatment for 12 to 18 months, cyclosporin A caused significant reductions in the glomerular filtration rate (before drug withdrawal, cyclosporin 97 +/- 18 vs placebo 125 +/- 16 ml min-1 1.73-m-2, p less than 0.05), renal plasma flow (454 +/- 83 vs 536 +/- 70 ml min-1 1.73-m-2, p less than 0.05), and lithium clearance (17 +/- 3 vs 28 +/- 5 ml min-1 1.73-m-2, p less than 0.05). The fractional proximal reabsorption was increased (0.82 +/- 0.03 vs 0.78 +/- 0.03, p less than 0.05), and the fractional distal sodium reabsorption reduced (0.88 +/- 0.03 vs 0.94 +/- 0.02, p less than 0.05). These results are in accordance with the hypothesis that the nephrotoxic effect of cyclosporin A results from a preferential constriction of afferent glomerular vessels. One year after withdrawal of the drug, all variables were similar in the two groups, except for blood glucose control which was worse in the cyclosporin A treated group. When corrected for differences in blood glucose control it appeared that in three out of nine patients glomerular filtration rate had not completely returned to the reference range of the placebo group. We conclude that the nephrotoxic side-effects of cyclosporin A treatment for 1 year are reversible. There are, however, signs of minor and perhaps chronic renal injury.

Microalbuminuria and diabetic complications in Chinese non-insulin-dependent diabetic patients: a prospective study

Urinary albumin excretion rate (AER) was monitored for periods of up to 3 years and 8 months with an ELISA method in 63 non-insulin-dependent diabetic Chinese subjects and was compared with 50 normal subjects. AER was 3.15 +/- 0.25 micrograms/min (M +/- SE) with a range of 0.27-8.40 micrograms/min for the normal subjects and 7.11 +/- 0.50 (2.11-19.45) micrograms/min for the diabetic subjects. The latter had significantly higher AER (P less than 0.0005). Age, sex, duration of diabetes, HbA1c and BMI did not correlate with AER in the diabetics. The presence of hypertension was found to be accompanied by an accelerated elevation of AER (5.96 +/- 1.58 vs 10.16 +/- 2.17 micrograms/min, at the beginning and at the end of the observation, respectively). Once hypertension became evident, control of blood pressure to a level comparable to that of the non-hypertensive group was not sufficient to halt the deterioration of urinary albumin excretion.

A microalbuminuria assay using bromphenol blue

A simple microalbuminuria assay using bromphenol blue/glycine reagent is described. Urine samples were prepared using gel filtration on Sephadex G-50 minicolumns and absorbance was measured at 610 nm 20 s after mixing 10 parts of eluate and 1 part of reagent. The detection limit of this method was 3 mg/l; within-run and between-run precision was between 0.5 and 4.1% for borderline and raised albumin concentrations. The recovery of albumin added to samples was 98.7 +/- 2.5%. Results obtained by this method correlated closely with values obtained by radial immunodiffusion (r = 0.987). The test is cheap (reagent costs about 5 cents) and suitable for the non-specialist laboratory.

An enzyme-linked immunoassay for human salivary albumin

An ELISA method has been developed for the determination of albumin in human parotid saliva. The range of sensitivity is 2-80 micrograms/l and it is suitable for use with volumes of 5 microliters or less of freshly collected parotid fluid, without prior sample preparation. Calibration data were fitted by microcomputer to an exponential function. The albumin concentration of parotid saliva was 1.9 +/- 1.53 mg/l, but levels fell on sample storage. Isoelectric focusing, followed by immunoblotting with antiserum to human serum albumin, showed identical double bands of pI 4.9-5.0 in albumin from both serum and saliva, thereby confirming that the antigens from the two sources are identical.

Partial normalization by dietary cod-liver oil of increased microvascular albumin leakage in patients with insulin-dependent diabetes and albuminuria

In a double-blind crossover study, we compared the effects of eight weeks of dietary supplementation with cod-liver oil with the effects of supplementation with olive oil on endothelial permeability, blood pressure, and plasma lipid levels in 18 patients with insulin-dependent diabetes mellitus and albuminuria. When the patients received the cod-liver-oil supplement, the mean (+/- SEM) transcapillary escape rate of albumin (as compared with the base-line rate) decreased from 8.7 +/- 0.5 to 6.9 +/- 0.6 percent per hour (P less than 0.01), and the blood pressure decreased from 146 +/- 4/90 +/- 2 mm Hg to 139 +/- 4/85 +/- 2 mm Hg (P less than 0.05). There was no correlation, however, between cod-liver oil's effect on the transcapillary escape rate of albumin and its effect on blood pressure. There was no change from base line after the patients received the olive-oil supplement. During dietary supplementation with cod-liver oil, the plasma concentration of high-density lipoprotein cholesterol increased and the concentrations of very-low-density lipoprotein cholesterol and triglycerides decreased (P less than 0.05 for all comparisons), but the level of low-density lipoprotein cholesterol did not change. In contrast, during supplementation with olive oil, the concentration of low-density lipoprotein cholesterol decreased and the levels of very-low-density lipoprotein cholesterol and triglyceride increased (P less than 0.05 for all comparisons), but there was no change in the level of high-density lipoprotein. No changes were observed in the glomerular filtration rate, degree of albuminuria, insulin requirement, glycosylated hemoglobin level, or blood glucose level during supplementation with either oil. We conclude that dietary supplementation with cod-liver oil lowers the elevated transcapillary escape rate of albumin characteristic of patients with insulin-dependent diabetes and albuminuria, independently of its effect on blood pressure--perhaps by decreasing vascular permeability. We did not find any effect of cod-liver oil on urinary albumin excretion.

Normal urinary albumin excretion in recently diagnosed type 1 diabetic patients

The urinary excretion of albumin and retinol binding protein were measured in 51 recently diagnosed Type 1 diabetic patients and 48 control subjects, matched for age and sex. The diabetic patients, admitted consecutively to the Steno Memorial Hospital, were all studied 3 to 6 months after the onset of diabetes. Urinary albumin excretion (median and 95% confidence interval) was similar in the diabetic patients and normal control subjects (8 (6-11) vs 8 (6-11) mg 24-h-1, NS). Four diabetic patients had urinary albumin excretion in the microalbuminuric range of 30-300 mg 24-h-1. There was no significant difference between the two groups in urinary excretion of retinol binding protein. The distribution among the individuals of both urinary proteins was positively skewed and similar in the two groups. In conclusion, no significant differences in the urinary excretion of albumin and retinol binding protein were found between recently diagnosed Type 1 diabetic patients and normal subjects.

Comparison of ultracentrifugation and a precipitation method for high-density lipoprotein cholesterol quantitation in insulin-dependent diabetic patients

We compared sodium phosphotungstic acid and magnesium chloride precipitation method for high-density lipoprotein (HDL) cholesterol quantitation with the ultracentrifugation method in 64 insulin-dependent diabetic patients with plasma triglyceride less than 3 mmol/l. The cholesterol content of HDL after precipitation of very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) was 86% +/- 3% of the cholesterol content of HDL (q greater than 1.063) determined after ultracentrifugation at q = 1.063 (1.33 +/- 0.05 mmol/l vs 1.55 +/- 0.06 mmol/l; p less than 0.001). HDL cholesterol determined after precipitation closely correlated to HDL cholesterol determined after ultracentrifugation (r = 0.97; p less than 0.001). The absolute difference between the HDL cholesterol values obtained by the two methods was correlated to HDL cholesterol (ultracentrifugation) (r = 0.75; p less than 0.001), but it was not correlated to VLDL cholesterol, LDL cholesterol, triglyceride, HbA1c, blood glucose or serum albumin. LDL cholesterol calculated by use of Friedewald's formula was 108% +/- 4% of the cholesterol content of LDL (q = 1.019 to 1.063), determined after ultracentrifugation, but the calculated and the ultracentrifugally determined LDL cholesterol values were closely correlated (r = 0.98; p less than 0.001). These results suggest that during sodium phosphotungstic acid and magnesium chloride precipitation of plasma from diabetic patients, a constant fraction of HDL cholesterol is co-precipitated, resulting in a systematic difference in HDL cholesterol quantitation when compared with the ultracentrifugation method.

A rapid and sensitive immunosorbent assay for urinary albumin

We describe a fast, simple and sensitive microtiter scale competitive ELISA for the determination of urinary albumin. All reagents are commercially available. In the standard procedure, a minimum concentration of 0.8 mg albumin/L can be measured, although, applying another dilution, 0.04 mg/L can be detected. Within-batch coefficient of variation was 6.9% and 5.6% (at 1:20 and 1:50 dilution, respectively); between-batch variation was 8.6% and 5.6% respectively. The influence of urine pH and other urine components is minimised in the assay diluting with a casein-containing buffer.

Elevated albumin excretion and retinal changes in children with type 1 diabetes are related to long-term poor blood glucose control

All diabetic children (n = 113) under 19 years old and with more than 2 years of diabetes attending the Steno Memorial Hospital in 1987 were studied. Normal urinary albumin excretion (less than 30 mg 24 h-1) was found in 96 patients (85%), 15 had microalbuminuria (30-300 mg 24 h-1) (13%), and 2 patients were proteinuric (greater than 300 mg 24 h-1) (2%). Retinal morphology was evaluated by colour fundus photography. Background retinopathy was more frequent in the group with elevated albumin excretion (71%) than in a matched normoalbuminuric group (20%, 2p less than 0.001). Long-term blood glucose control was assessed from all previous HbA1c measurements in the hospital records, an average of nine per patient. The mean observation period was 48 (3-76) months. Children with elevated albumin excretion had a higher mean HbA1c than children with normal urinary albumin excretion (10.3 +/- 1.9 vs 9.2 +/- 1.3% (+/- SD), 2p less than 0.05). Children with retinopathy had an HbA1c of 9.9 +/- 1.7 vs 9.0 +/- 1.2% in patients without retinopathy (2p less than 0.01).

The effects of cimetidine on creatinine excretion, glomerular filtration rate and tubular function in renal transplant recipients

The renal clearance of endogenous creatinine (CCr), sodium (CNa) and lithium (CLi) was determined before and after a single intravenous bolus of cimetidine in nine renal transplant recipients. The glomerular filtration rate (GFR) was measured with 125I-iothalamate clearance (CTh). The initial CCr of 65 ml/min (median) was reduced to a nadir of 46 ml/min (p less than 0.01) during the first 2 h after infusion of cimetidine. GFR remained unchanged, and thus the fractional clearance of creatinine (CCr/CTh) was reduced from 1.43 (median) to 1.03 (p less than 0.01). CNa and the fractional excretion of sodium decreased throughout the study (p less than 0.05); CLi was unchanged. In conclusion cimetidine, when measured during 1-h clearance periods, interferes with tubular creatinine secretion in the denervated kidney of transplant recipients without affecting the glomerular filtration rate or proximal tubular flow. This suggests that on-going cimetidine treatment must be taken into account when graft function is evaluated by the CCr alone.

Albuminuria reflects widespread vascular damage. The Steno hypothesis

Albuminuria in Type 1 (insulin-dependent) diabetes is not only an indication of renal disease, but a new, independent risk-marker of proliferative retinopathy and macroangiopathy. The coincidence of generalised vascular dysfunction and albuminuria, advanced mesangial expansion, proliferative retinopathy, and severe macroangiopathy suggests a common cause of albuminuria and the severe renal and extrarenal complications associated with it. Enzymes involved in the metabolism of anionic components of the extracellular matrix (e.g. heparan sulphate proteoglycan) vulnerable to hyperglycaemia, seem to constitute the primary cause of albuminuria and the associated complications. Genetic polymorphism of such enzymes is possibly the main reason for variation in susceptibility.

Features of endothelial dysfunction in early diabetic nephropathy

The release of tissue plasminogen activator (tPA) by vascular endothelial cells during exercise was studied in forty men with insulin-dependent diabetes. Three groups, matched for age and diabetes duration, were defined as: group I (n = 19), normal urinary albumin excretion (less than 30 mg/24 h); group II (n = 11), incipient diabetic nephropathy (30-300 mg albumin excreted per 24 h); and group III (n = 10), clinical diabetic nephropathy (more than 300 mg albumin excreted per 24 h). Nine non-diabetic men served as controls. The rise in tPA antigen with exercise was similar in the controls and group I but significantly smaller in groups II and III (p less than 0.01). The albumin transcapillary escape rate was significantly higher in groups II and III than in group I and normal controls (p less than 0.01). The basal plasma level of von Willebrand factor was higher in groups III (p less than 0.01) and II (difference not significant, p = 0.06) than in group I and normal controls. These findings suggest that insulin-dependent diabetic patients with only slightly raised urinary albumin excretion have general endothelial cell dysfunction or damage. It is not yet clear whether these changes are important in the pathogenesis of thrombosis and atherosclerosis in these patients.

Early renal involvement and nephropathy. Can treatment modalities be predicted from identification of risk factors in diabetics?

There is now circumstantial evidence indicating that initiation and progression of renal disease in diabetes is associated with the degree of metabolic control, although modifying factors, such as elevation of blood pressure and, possibly, dietary protein intake, are important. Further, there is differential susceptibility, and more studies are clearly needed to clarify why some patients develop nephropathy and others do not, despite similar metabolic control. Metabolic control, blood pressure level and protein intake are probably not only risk factors but are also involved in the pathogenesis of diabetic nephropathy. Thus, intervention by optimizing glycaemic control and blood pressure treatment and by low-protein diets appears possible and can be recommended as a prudent treatment programme. Early clinical detection of patients at risk for late nephropathy is already possible, since easy, rapid, inexpensive methods for detecting microalbuminuria are now available.

"Intact nephrons" as the primary origin of proteinuria in chronic renal disease. Study in the rat model of subtotal nephrectomy

Single nephron filtration rate of albumin (SNGFRAlb) was measured in remnant nephrons of Munich-Wistar rats 4-6 wk after subtotal nephrectomy (NPX). Serial thin-section histological analysis was then conducted on the same glomeruli by light microscopy. SNGFRAlb ranged from 1 to 15 times normal. However, a direct relationship between abnormalities of structure and function was not seen, e.g. the glomeruli with the fewest structural abnormalities and marked hyperfiltration often had the highest SNGFRAlb. Moreover, the majority of glomeruli had minimal structural abnormalities. Normalization of the markedly elevated glomerular capillary pressure (PGC) in these glomeruli was accomplished by acute intravenous infusion of verapamil, which decreased SNGFRAlb by 9-83% without affecting the single nephron filtration rate of water (SNGFRH2O). 1-2 wk after subtotal NPX, all glomeruli were hyperfiltering and had elevated PGC. The fractional clearance of larger (greater than 36 A) dextrans was selectively increased in these glomeruli that lacked discernible damage by light microscopy. Verapamil normalized PGC, reduced proteinuria to 48 +/- 4% of baseline, and improved glomerular size selectivity without altering SNGFRH2O. Proteinuria after subtotal NPX thus originates largely from glomeruli with minimal structural abnormalities. The defect in size selectivity is largely attributed to the prevailing high PGC, producing large, nonselective channels on the glomerular capillary wall. The observations raise the possibility that in chronic renal diseases, the reduction in proteinuria often seen after therapeutic measures, including antihypertensive medication, may reflect their functional effect on the relatively intact glomeruli rather than their structure-sparing effect on severely damaged glomeruli, which contribute little to the proteinuria.

Improved metabolic control does not alter the charge-dependent glomerular filtration of albumin in uncomplicated type 1 (insulin-dependent) diabetes

The selectivity index, i.e. clearance of non glycated albumin/clearance of glycated albumin was studied in fourteen patients with Type 1 (insulin-dependent) diabetes and normal urinary albumin excretion. The index was increased above one in all patients, and correlated significantly to HbA1c. It was, however, unaffected by 12 weeks of improved metabolic control with a mean decline in HbA1c of 1.9% in seven patients. We conclude that the increased electronegative charge of the glomerular filtration barrier observed in uncomplicated diabetes is related to long term metabolic control but not reversible during twelve weeks of strict metabolic control. This indicates a slow turnover of the components responsible for the increased charge selectivity in uncomplicated diabetes.

Impaired aerobic work capacity in insulin dependent diabetics with increased urinary albumin excretion

To assess whether decreased aerobic work capacity was associated with albuminuria in insulin dependent diabetics aerobic capacity was measured in three groups of 10 patients matched for age, sex, duration of diabetes, and degree of physical activity. Group 1 comprised 10 patients with normal urinary albumin excretion (less than 30 mg/24 h), group 2 comprised 10 with incipient diabetic nephropathy (urinary albumin excretion 30-300 mg/24 h, and group 3 comprised 10 with clinical diabetic nephropathy (urinary albumin excretion greater than 300 mg/24 h). Ten non-diabetic subjects matched for sex, age, and physical activity served as controls. Oxygen uptake was similar in the four groups at rest and during a 75 W workload. Maximal oxygen uptake was also similar in the control subjects and group 1 (median 41.7, (range 29.1-53.0) ml/kg/min v 38.5 (26.6-59.2) ml/kg/min, respectively), but was significantly lower in group 2 (27.7 (13.9-44.3) ml/kg/min) and group 3 (22.6-36.7) ml/kg/min). The difference in maximal oxygen uptake between groups 1 and 2 was 10.8 ml/kg/min (95% confidence interval 3.6 to 23.4 ml/kg/min) and between groups 1 and 3, 11.7 ml/kg/min (4.9 to 22.5 ml/kg/min). These differences were not explained by differences in metabolic control or the degree of autonomic neuropathy. Thus the insulin dependent diabetics with only slightly increased urinary albumin excretion had an appreciably impaired aerobic work capacity which could not be explained by autonomic neuropathy or the duration of diabetes. Whether the reduced capacity is due to widespread microangiopathy or another pathological process affecting the myocardium remains to be established.

Abnormalities in plasmas concentrations of lipoproteins and fibrinogen in type 1 (insulin-dependent) diabetic patients with increased urinary albumin excretion

Type 1 (insulin-dependent) diabetic patients with clinical nephropathy have a more than ten-fold increase in mortality of cardiovascular diseases compared with diabetic patients without nephropathy. The risk factors for cardiovascular disease, plasma concentrations of lipoproteins and fibrinogen, were investigated in 74 long-term diabetic patients: 37 with normal urinary albumin excretion, 20 with incipient nephropathy and 17 with overt clinical nephropathy based on urinary albumin excretion. The groups were matched according to sex, age and diabetes duration. The concentration of plasma cholesterol, very low density lipoprotein cholesterol, low density lipoprotein cholesterol, triglyceride and fibrinogen rose with increasing urinary albumin excretion. The plasma concentrations of these lipoproteins and fibrinogen were 11-14% higher in the patients with incipient nephropathy and 26-87% higher in the patients with overt clinical nephropathy compared with the patients without nephropathy. The plasma concentration of high density lipoprotein cholesterol was unaffected by albuminuria. Patients with normal urinary albumin excretion and HbA1c greater than 8.0% had significantly higher very low density lipoprotein- and lower high density lipoprotein cholesterol concentrations compared with patients with HbA1c less than 8.0%. Simple addition of the described risk factors can only account for a minor part of the greatly increased cardiovascular mortality in patients with diabetic nephropathy. An additional and possibly more decisive factor might be a change in the arterial wall, a change which promotes lipid accumulation and/or facilitates thrombus formation.

Glomerular size and charge selectivity in insulin-dependent diabetes mellitus

The pathogenesis of clinical nephropathy in Type 1 (insulin-dependent) diabetes was investigated by measuring renal fractional clearances of albumin, total IgG, IgG4 and beta 2-microglobulin, four plasma proteins which differ in size and charge. Seventy patients and eleven control subjects were studied. In diabetic patients with normal urinary albumin excretion (less than 30 mg/24 hr), fractional IgG clearance was two to three times higher than in control subjects, whereas fractional clearance of the anionic plasma proteins IgG4 and albumin was similar to that of control subjects. These alterations indicate an increase in anionic pore charge within the glomerular basement membrane concomitant with an increase in either pore size or impairment of tubular reabsorption. Diabetic patients, whose urinary albumin excretion has started to rise (30 to 100 mg/24 hr), had unchanged fractional IgG compared to patients with normal albumin excretion, while fractional IgG4 and albumin clearances were increased three- to fourfold; indicating unchanged glomerular pore size, but a decrease in anionic pore charge. In patients demonstrating urinary albumin excretion of greater than 100 mg/24 hr fractional IgG clearance increased to the same extent as fractional albumin clearance, indicating an increase in large pore area. Fractional beta 2-microglobulin clearances were similar to that of control subjects in the different patient groups indicating unchanged tubular reabsorption of proteins. Thus, the increase in large pore area seen in patients with clinical nephropathy is preceded by loss of anionic charge in the glomerular basement membrane. It is likely that this loss of anionic charge is due to loss of heparan sulphate-proteoglycan.

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.

Comparison of overnight, morning and 24-hour urine collections in the assessment of diabetic microalbuminuria

With the aim of comparing different urine collection periods in the assessment of micro-albuminuria, urinary albumin excretion rates (AERs) were measured in samples from 24 h, overnight, and morning urine collections in 54 patients aged 17 to 62 years with insulin-dependent diabetes mellitus with a mean duration of 15 years. The AER in overnight urine was found to be reduced by 25% compared to the rate in 24 h and morning urine. Assessing the ability to predict a 24 h AER within the microalbuminuric range (20-200 micrograms/min) we found a sensitivity of 90% and a specificity of 88% for both overnight and morning urine samples. These values were slightly improved by relating AER to the excretion of creatinine and it is concluded that overnight as well as morning urine collections can be used when diagnosing microalbuminuria in insulin-dependent diabetics. Furthermore the results show that the albumin to creatinine ratio in morning urine is a reliable estimate of 24 h AER and better than measurement of the albumin concentration alone.

The variability of overnight urinary albumin excretion in insulin-dependent diabetic and normal subjects

The variability of overnight urinary albumin excretion rate (AER) and albumin to creatinine ratio was assessed in eight normal subjects and two groups of insulin-dependent diabetic patients divided on the basis of an initial overnight urinary albumin excretion rate below (n = 15) or above (n = 12) 30 micrograms/min. The latter group is known to be at risk of developing clinical diabetic nephropathy. An albumin to creatinine ratio of 2.6 and above identified all patients with an initial albumin excretion rate greater than 30 micrograms/min. The mean of the coefficients of variation, calculated from five successive overnight urine collections, for all subjects was 38% for albumin excretion rate and 37% for albumin to creatinine ratio. There was no significant difference in the variation of albumin excretion rate and albumin to creatinine ratio within or between the groups. Subsequent AERs from diabetics with an initial rate greater than 30 micrograms/min changed category more often (chi 2 = 11.9, p less than 0.001) than those from diabetics with lower initial rates and normal subjects. This was due to four subjects with initial values close to the cut-off level, whose subsequent values varied around it. Albumin excretion rates in normal subjects never exceeded 11 micrograms/min. Whether a patient's risk status is influenced by the degree of variation of albumin excretion rate around a risk level, or whether the classification of risk is improved by multiple collections, awaits testing in prospective subjects.

Central role for sodium in the pathogenesis of blood pressure changes independent of angiotensin, aldosterone and catecholamines in type 1 (insulin-dependent) diabetes mellitus

We studied 73 Type 1 (insulin-dependent) diabetic patients, 18 to 50 years of age, with a diabetes duration of more than five years. Group 1: normal urinary albumin excretion below 30 mg per 24 h (n = 19); group 2: microalbuminuria, 30-300 mg per 24 h (n = 36); and group 3: diabetic nephropathy, above 300 mg per 24 h (n = 18). Fifteen nondiabetic persons matched for sex and age served as control subjects. The sodium intake evaluated on the basis of 24-h urine sodium excretion was similar in patients and control subjects. Blood pressure in groups 1 and 2 and control subjects was below 160/95 mmHg. The blood pressure was increased in group 3 as compared with the other groups (systolic/diastolic 161 +/- 22/101 +/- 9 mmHg vs 131 +/- 13/84 +/- 10, mean +/- SD, p less than 0.0001). Exchangeable sodium was increased in patients (p less than 0.01) and correlated to the mean blood pressure (n = 70, r = 0.41, p less than 0.01). Extracellular volume was increased in patients (p less than 0.05), whereas plasma volume was normal. Supine serum angiotensin II was suppressed in the patients (p less than 0.001). A negative correlation was found between mean blood pressure and supine serum aldosterone (n = 68, r = -0.24, p less than 0.05), and exchangeable sodium and aldosterone (n = 66, r = -0.36, p less than 0.002) in all patients. The catecholamine levels were also suppressed or normal in the patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Microalbuminuria in insulin-dependent diabetes: prevalence and practical consequences

Urinary albumin excretion in a representative sample of 679 patients with Type I (insulin-dependent) diabetes, 18 to 50 years of age, was investigated. Patients on antihypertensive therapy were excluded. Urinary albumin excretion was examined in one 24 hour urine sample using an ELISA technique. Twenty-three per cent of the patients had microalbuminuria, i.e., 30-300 mg albumin/24 h. The prevalence of microalbuminuria was independent of sex, age, insulin dose and diabetes duration. In the majority of those cases in which microalbuminuria was found during the first 10 years of diabetes, the concentrations were in the lower range, i.e., 30-50 mg/24 h. The prevalence of incipient nephropathy (urinary albumin excretion in a single urine sample of 51-300 mg/24 h) increased with diabetes duration. In patients with incipient nephropathy hemoglobin A1c tended to be, and blood pressure was, elevated compared with age, sex, and duration matched patients with normal urinary albumin excretion rates (p = 0.08 and p less than 0.001, respectively). Urinary albumin excretion and blood pressure were significantly correlated in the total group (n = 401, r = 0.2, p less than 0.001). On the basis of these findings practical guidelines for the handling of patients with microalbuminuria are proposed.

A solid phase enzyme immunoassay for the measurement of urinary albumin and the detection of microalbuminuria

A test for the measurement of trace urinary albumin concentrations, which is suitable for the detection of microalbuminuria, was developed. The technique is an indirect enzyme-linked assay (ELISA) in which a fixed amount of anti-albumin antibody is placed into polystyrene tubes coated with human albumin, together with the urine sample to be tested. The albumin in the test specimen competes with the solid-phase albumin for binding to the added antibody. The test is precise (inter- and intra-assay coefficients of variation were 8.2% and 7.8%, respectively), accurate (mean recovery 102-106% for two human albumin preparations), and sensitive (detection limit 0.9 micrograms/ml). These characteristics are not dissimilar from those of the radioimmunoassay reported in the literature, with the advantages of being completely safe, easy to perform, and not requiring expensive equipment. Using this assay the urinary albumin excretion in 20 normal subjects was found to be 2.5 +/- 2.2 micrograms/min (range 0.9-7.5 micrograms/min) after 8 hours of bed rest and 4.5 +/- 5.7 micrograms/min (range 1.5-2.0 micrograms/min) after 8 hours of moderate physical activity.

ELISA for determination of albumin in the nanogram range: assay in cerebrospinal fluid and comparison with radial immunodiffusion

An ELISA double antibody sandwich technique on polystyrene microtiter plates for quantitation of albumin in cerebrospinal fluid is described. Commercially available reagents are used for this assay, in which albumin in the range between 0.1-1 ng/100 microliters can easily be detected. Albumin determinations in 30 CSF samples by this method revealed concentrations of 0.1-0.8 mg/ml. Results obtained by ELISA correlated significantly with those from parallel experiments with commercially available RID assays. The ELISA described is a sensitive, simple, and expeditious assay for determination of albumin in the nanogram range and may be a promising method for routine analysis of albumin concentrations in CSF.

Transcapillary escape rate and relative metabolic clearance of glycated and non-glycated albumin in type 1 (insulin-dependent) diabetes mellitus

The transcapillary escape rate and relative plasma disappearance of glycated and non-glycated albumin were measured in 25 male Type 1 (insulin-dependent) diabetic patients using a double tracer technique. The patients were divided into three groups on the basis of their urinary albumin excretion: group 1, normal albumin excretion (less than 30 mg/24 h) (n = 8); group 2, microalbuminuria (30-300 mg/24 h) (n = 9); and group 3, clinical nephropathy (greater than 300 mg/24 h) (n = 8). Six male age-matched non-diabetic persons served as control subjects. The transcapillary escape rate of glycated albumin was similar in group 1 and control subjects (4.7 +/- 2.1 versus 5.1 +/- 1.7%), but significantly increased in group 2 (7.0 +/- 1.7%, p less than 0.05) and in group 3 (7.9 +/- 3.1%, p less than 0.05). The transcapillary escape rate of glycated albumin was slightly lower than that of non-glycated albumin in all groups, but significant only in normal control subjects. No difference in the catabolic rate of glycated and non-glycated albumin was found. We conclude that the in vivo effects of glycation on the clearance and transcapillary passage of albumin are small and not likely to play any significant role in the development of late diabetic microvascular complications.

Effect of two years of strict metabolic control on progression of incipient nephropathy in insulin-dependent diabetes

36 patients with insulin-dependent diabetes mellitus who had 'Albustix'-negative urine but raised urinary albumin excretion (30 to 300 mg/24 h) were randomly assigned to either remaining on conventional insulin treatment or continuous subcutaneous insulin infusion and followed up for 2 years. The insulin-infusion group showed a significant, sustained improvement in metabolic control, with a median glycosylated haemoglobin of 7.2% (range 5.9-8.8), but there was no change in the conventional-treatment group (median 8.6%, range 7.2-13.4) (p less than 0.001). Clinical diabetic nephropathy (a urinary albumin excretion rate above 300 mg/24 h in at least two of three 24 h urine collections) developed in 5 patients in the conventional-treatment group, but not in the insulin-infusion group (p less than 0.05, two-tailed). Fractional albumin clearance (mean and range X 10(7] increased in the conventional-treatment group from 160 (35-468) to 360 (29-1580) and was unchanged in the insulin-infusion group (170 [31-608] before to 160 [26-460] after) (p less than 0.05). Insulin infusion had an overall beneficial effect on the annual increase in urinary albumin excretion (p less than 0.05), and the mean glycosylated haemoglobin values correlated positively with annual change in albumin excretion (r = 0.57, p less than 0.0001). The diastolic blood pressure rose significantly in the conventional-treatment group (p less than 0.001), and annual change in mean blood pressure correlated with change in urinary albumin excretion (r = 0.49, p less than 0.001).

Beta 2-microglobulin in urine and serum determined by a micro-ELISA technique

An enzyme-linked immunoadsorbent assay for the determination of beta 2-microglobulin in serum and urine using microtest plates as solid phase is described. All reagents are commercially available. The assay has a high capacity and it is inexpensive using only 3% of the amounts of antibodies required in a previously described ELISA based on tubes as solid phase.

Evidence of changes in renal charge selectivity in patients with type 1 (insulin-dependent) diabetes mellitus

Altered filtration of macromolecules due to decreased electrical charge of the glomerular basement membrane might be the initial step in the development of albuminuria in patients with Type 1 (insulin-dependent) diabetes mellitus. We therefore investigated the selectivity index, i.e. renal clearance of non-glycated plasma albumin/clearance of glycated plasma albumin in 38 patients with Type 1 diabetes mellitus. The two albumin molecules differed slightly in charge, non-enzymatic glycated albumin being more anionic at physiological pH compared with unmodified plasma albumin. Glycated albumin in plasma and urine was determined by a specific, sensitive and highly reproducible chromatographic procedure. In diabetic patients with normal urinary albumin excretion, the selectivity index was increased three-fold compared with that of non-diabetic subjects (2 p less than 0.01). A significant correlation (r = 0.53, 2 p less than 0.01) between haemoglobin A1c and selectivity index was demonstrated in these patients, indicating a change in charge-dependent renal filtration could possibly be attributed to non-enzymatic glycation of components in the glomerular basement membrane and tubuli. Diabetic patients with increased albumin excretion rate had a significantly lower selectivity index compared with patients with normal albumin excretion (2 p less than 0.01). A significant negative correlation (r = 0.85, 2 p less than 0.001, exponential curve fit) was seen between urinary albumin excretion and selectivity index in the diabetic patients, indicating that the capability of differentiating between macromolecules of different charges is again lost with increasing urinary albumin excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased transcapillary escape rate of albumin in type 1 (insulin-dependent) diabetic patients with microalbuminuria

The transcapillary escape rate, intravascular mass and outflux of albumin were measured in 75 Type 1 (insulin-dependent) diabetic patients. The groups were defined as: group 1: normal urinary albumin excretion, less than 30 mg/24 h (n = 21); group 2: microalbuminuria, 30-300 mg/24 h (n = 36); group 3: diabetic nephropathy, less than 300 mg/24 h (n = 18). Fifteen sex- and age-matched non-diabetic persons served as control subjects. The diabetes duration was: group 1: 20 +/- 9 years, group 2: 17 +/- 5 years, group 3: 19 +/- 7 years. The transcapillary escape rate of albumin was similar in controls and group 1 (5.0 +/- 1.8 versus 5.2 +/- 1.5%) and was significantly higher in the microalbuminuric group 2 and group 3 (8.1 +/- 2.2 versus 8.1 +/- 2.3%). The differences were not explained by differences in metabolic control or blood pressure at the time of investigation. The outflux of albumin was also higher in group 2 than in group 1 and controls (7.1 +/- 2.0 versus 5.3 +/- 1.5 and 5.1 +/- 2.0 g/h X 1.73 m2). It was indistinguishable from controls in group 3 (5.8 +/- 1.5 g/h X 1.73 m2) because of a reduced intravascular mass of albumin (p less than 0.01) in group 3. In conclusion, a universal vascular leakage of albumin is an early event in the development of diabetic nephropathy, with the leakage of albumin being fully developed in the microalbuminuric patient. In contrast, long-term diabetic patients with normal urinary albumin excretion have a normal transcapillary escape rate of albumin.

Kidney function during 12 months of strict metabolic control in insulin-dependent diabetic patients with incipient nephropathy

Thirty-six patients with insulin-dependent diabetes mellitus who had Albustix-negative urine but elevated urinary albumin excretion (30 to 300 mg per 24 hours) were matched in pairs according to their urinary albumin level, blood glycosylated hemoglobin level, and sex and assigned randomly to either unchanged conventional treatment or continuous insulin infusion. During the next 12 months a significant improvement in glycemic control was observed in the insulin-infusion group, with a reduction in the mean glycosylated hemoglobin level from 9.5 to 7.3 percent. There was no change in the control group (9.3 to 9.2 percent). No significant change in albumin excretion was observed in either group. The mean blood pressure increased slightly in both groups (from 98 to 101 mm Hg in the insulin-infusion group and from 98 to 103 mm Hg in the control group). Kidney size was significantly reduced in all patients during insulin infusion, but no consistent change was observed in the control group. No significant change was observed in the glomerular filtration rate. Our data suggest that the pathologic processes causing microalbuminuria in early renal disease are not reversed during 12 months of strict metabolic control.