Intermittent diabetic microalbuminuria: association with blood pressure, glycemic control, and protein intake

Microalbuminuria as identified by a spot morning urine specimen in non-insulin-treated diabetes: an eight-year follow-up study

This study followed up a cohort of patients with microalbuminuria identified on a spot morning urine sample 8 years earlier and aimed to determine if a spot morning urinary albumin concentration was able to identify patients with non-insulin treated diabetes at increased risk of mortality and progression to nephropathy. In 1984, 47 of 216 patients chosen by random selection from our teaching hospital-based diabetes clinic were identified as having microalbuminuria (urinary albumin concentration 35-300 micrograms ml-1). Subjects were compared with an age-matched control group from the 1984 cohort who did not have microalbuminuria. Eight years later, 22 of 47 (46.8%) patients with microalbuminuria had died compared to 10 of 47 (21.3%) patients without albuminuria (p < 0.05). The majority of deaths were from cardiovascular disease (53.1%). Logistic regression showed microalbuminuria to be an independent predictor of mortality, not influenced by age, duration of diabetes, blood pressure, glycosylated haemoglobin or creatinine at the initial examination. Eight years later, in the group with initial microalbuminuria, eight still had microalbuminuria and five patients had developed nephropathy. In the group without albuminuria in 1984, only one patient had progressed to microalbuminuria and no patients to nephropathy. In conclusion, a spot urinary albumin concentration is of value in identifying patients with an increased risk of mortality or progression to nephropathy, and is simple to obtain at a clinic.

Is a random urinary albumin concentration a useful screening test in insulin-treated diabetic patients?

The debate continues on how to screen for microalbuminuria in clinical practice in patients with insulin-dependent diabetes mellitus. Our study assesses the value of a spot morning urine specimen obtained at a clinic visit. In 1984, as part of a randomised survey of our diabetes clinic, 43 of 249 patients with insulin treated diabetes mellitus, were found to have microalbuminuria (urinary albumin concentration 35-300 ug ml-1) on a spot morning urine sample. These subjects were compared with an age-matched control group from the 1984 cohort who did not have microalbuminuria. Eight years later, in the group with microalbuminuria, 10 had died compared to six in the control group (p = 0.17) with 62.5% of all deaths being from cardiovascular disease. In the group with microalbuminuria, 10 of 27 still had incipient nephropathy while five had progressed to nephropathy. In the group without microalbuminuria only three of 33 patients had progressed to microalbuminuria while none had progressed to nephropathy. In conclusion a spot morning urine sample is a useful screening test to identify patients at risk of progression to nephropathy.

An examination of the covariability of subclinical albuminuria in insulin-dependent diabetes mellitus: implications for monitoring microalbuminuria

We examined the covariability of subclinical albuminuria in a cohort of 160 insulin-dependent diabetics who underwent simultaneous measurements of overnight urinary albumin excretion rate (UAV) and several clinical variables on 7 occasions over a period of 18 months. After allowing for within-patient correlation between visits, significant within-patient associations were found between UAV and variations in tobacco consumption (regression coefficient = 0.006, S.E. = 0.002, P = 0.02), insulin dose (regression coefficient = 0.003, S.E. = 0.001, P = 0.01) and creatinine clearance (regression coefficient = 0.776, S.E. = 0.047, P < 0.0001); the association between UAV and creatinine clearance was not influenced by adjusting for urine flow rate. No significant associations were found between UAV and changes in blood pressure, glycaemic control or other variables. We then focused on 33 patients with intermittent microalbuminuria, defined as a UAV > 30 micrograms/min on at least one occasion, but not exceeding 3 consecutive occasions. These patients had a total of 52 episodes of microalbuminuria which were significantly associated at the 5% level with increases in creatinine clearance (P = 0.02), but not with changes in other variables. Our findings did not differ in patients with intermittent microalbuminuria defined with reference to a cut-off UAV of 20 micrograms/min. We conclude that changes in glomerular filtration rate (as reflected by creatinine clearance) may partly account for the within-patient variability in subclinical albuminuria in insulin-dependent diabetics, and that variables routinely measured in the clinic are not useful for deciding when to monitor patients for microalbuminuria.

Prediction of persistent microalbuminuria in patients with diabetes mellitus

Persistent microalbuminuria [albumin excretion rate (AER): 30-300 micrograms/min] is predictive of clinical nephropathy in patients with insulin-dependent diabetes mellitus (IDDM) and cardiovascular mortality in addition to nephropathy in patients with non-insulin-dependent diabetes. The clinical significance of intermittent microalbuminuria, however, is unknown. We performed serial measurements of urinary albumin excretion at intervals of approximately 6 months in 139 diabetic patients who at entry did not have persistent microalbuminuria to determine whether intermittent microalbuminuria occurs more frequently in those patients who subsequently develop persistent microalbuminuria. The relative risk for the development of persistent microalbuminuria in diabetic patients with a greater proportion than 3 out of 20 determinations in the microalbuminuric range was 17.4 (95% confidence interval, 3.92-77.2) in those with IDDM and 2.78 (0.99-7.8) in those with non-insulin-dependent diabetes when compared with matched diabetic patients with fewer elevated measurements. These data suggest that frequent intermittent microalbuminuria predicts the future development of persistent microalbuminuria particularly in IDDM patients and that AER should be assessed by serial rather than single measurements.

The predictive value of albuminuria for cardiovascular and renal disease. A 5-year follow-up study of 476 patients with type I diabetes mellitus

A 5-year follow-up study of 476 type I adult diabetic patients previously studied cross sectionally revealed that, during the observation period, 19 patients died and 30 developed cardiovascular or renal disease, such as myocardial infarction (n = 8), cerebrovascular disease (n = 3), amputation (n = 6), and renal insufficiency (n = 13). The patients were registered by one and the most-severe event only. The yearly death rate was 8.0 per 1000, compared with the expected death rate of 2.0 for people with corresponding age and sex in the general population. In patients with renal insufficiency, one also had myocardial infarction, and one had had an amputation. The ages of patients who died, with myocardial infarction, cerebrovascular disease, amputation, or renal insufficiency, were 44.2 +/- 12.7, 41.3 +/- 6.6, 43.7 +/- 13.2, 45.3 +/- 15.7, and 40.8 +/- 9.8 years, respectively. Urinary albumin concentration in a single early morning urine sample was found to be a strong prognostic marker for the development of cardiovascular disease or death. In contrast, age, gender, age at onset and duration of diabetes, levels of blood pressure, serum creatinine, and HbA1c, or presence of hypertension, as well as changes in blood pressure and hBa1c, during the observation period did not influence the survival or incidence of cardiovascular disease. However, blood pressure and HbA1c were associated with increased urinary albumin concentrations during the follow-up period.

Morbidity, mortality, and albuminuria in type 2 diabetic patients: a three-year prospective study of a random cohort in general practice

In a 3-year prospective study, the prevalence of albuminuria and its relationship to macrovascular disease, pre-existing vascular risk factors and mortality rate were studied in a random cohort of 290 patients with Type 2 diabetes mellitus in general practice. Newly occurring micro- or macroalbuminuria was associated with significantly (p less than 0.05) higher systolic blood pressure: median (IQ range) 157 (140-170) vs 150 (130-160) mmHg, in addition to higher serum triglycerides: median (IQ range) 2.71 (1.84-4.25) vs 1.84 (1.35-3.14) mmol l-1, and C-peptide levels: median (IQ range) 1.30 (0.98-2.16) vs 1.10 (0.82-1.58) nmol l-1, at 3-year follow-up. Patients with macroalbuminuria at final examination had significantly higher systolic and diastolic blood pressure, serum triglyceride and beta 2-microglobulin levels, decreased HDL-cholesterol, and a significantly higher prevalence of carotid artery stenoses and peripheral vascular disease. Patients dying from vascular causes showed significantly higher urinary albumin levels at entrance as compared to the surviving patients: median (IQ range): 42.2 (11-249.7) vs 10.4 (4.6-28.0) mg l-1, p less than 0.008, and overall mortality rate was significantly linked with the presence of macroalbuminuria (26% vs 5% in normoalbuminuric patients). A comparison between the results of the initial and the final examination indicated an overall worsening of renal variables (albuminuria: median (IQ range): female 9.5 (4.5-21) vs 13.4 (5.1-39.7) mg l-1, (p less than 0.05); male 13.8 (4.7-34.1) vs 32.6 (8.1-78.7) (p less than 0.001), despite a significant improvement in metabolic variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary albumin, transferrin and iron excretion in diabetic patients

The present study was undertaken to determine urinary and serum iron, transferrin and albumin levels in diabetic patients with varying amounts of proteinuria. A highly significant correlation was found between urinary albumin and transferrin excretion over a wide range of urinary albumin excretion (0.005 to 18 g/g creatinine) (r = 0.972). The urine/serum ratio of transferrin and albumin were identical, documenting a similar glomerular leak and tubule handling for these two proteins. In contrast to the above correlation between transferrin and albumin, there was no correlation between iron and either of these proteins until nephrotic range proteinuria had occurred, and even at that time the correlation was much weaker than that found between the proteins (r = 0.680). Urinary iron excretion increased early in the course of diabetic renal disease, being increased in 3 of 11 patients without proteinuria and in 8 of 10 patients with mild proteinuria. All patients with nephrotic range proteinuria had markedly increased urinary iron excretion (150 +/- 166 micrograms/g creatinine vs. 6.4 +/- 0.7 micrograms/g creatinine in controls) and decreased serum iron levels (592 +/- 189 micrograms/liter vs. 979 +/- 394 micrograms/liter in the control group). The iron/transferrin ratio in urine was consistently greater than the iron/transferrin ratio in plasma at all stages of proteinuria. In patients with both subnephrotic and nephrotic range proteinuria, approximately 35 to 40 micrograms Fe/g creatinine was present in the urine with an excess of transferrin. In conclusion, urinary iron excretion is increased early in the course of diabetic renal disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Triphasic changes in selectivity with increasing proteinuria in type 1 and type 2 diabetes

Two indices of the selectivity of proteinuria, the immunoglobulin G (IgG)/albumin and the IgG/transferrin clearance ratios, were studied cross-sectionally and serially over 7 years in a cohort of 52 Type 1 and 60 Type 2 diabetic patients without established diabetic nephropathy. In Type 1 and Type 2 diabetic patients with albuminuria less than 30 micrograms min-1, both protein clearance ratios were significantly higher than in 27 control subjects. As albuminuria increased, there was a decrease in both protein clearance ratios. However, at albumin clearances above 90 nl s-1, equivalent to albumin excretion rates of greater than 250 micrograms min-1, a positive correlation was found in Type 2 diabetic patients between protein clearance ratios and albuminuria. In individual Type 1 and Type 2 diabetic patients with progressively increasing proteinuria, serial measurements of selectivity showed a decline in both protein clearance ratios with the onset of microalbuminuria. Episodes of transient microalbuminuria were also associated with a fall in the IgG/albumin clearance ratio. The results suggest that the selectivity of proteinuria undergoes a triphasic change with the development of diabetic nephropathy. In the first phase, proteinuria is non-selective with IgG clearance equal to or exceeding transferrin or albumin clearance. As microalbuminuria develops, there is a progressive increase in selectivity reflecting the preferential excretion of transferrin and albumin compared with IgG. In later stages of nephropathy, as shown in Type 2 diabetic patients with macroalbuminuria, there is a return to non-selective proteinuria.