OBJECTIVE— To describe the natural history and risk factors for persistent microalbuminuria in children and adolescents with type 1 diabetes followed for up to 15 years.

RESEARCH DESIGN AND METHODS— This study contained a longitudinal cohort of 972 patients; analysis of baseline risk factors was performed using logistic regression and predictors over time using survival analysis. Albumin excretion rate was measured on three consecutive timed overnight urine collections on at least two occasions. Normoalbuminuria was defined as a median albumin excretion rate <7.5 μg/min, borderline microalbuminuria as 7.5–20 μg/min, and microalbuminuria as 20–200 μg/min. Microalbuminuria was further classified as persistent if its duration was >12 months. Median age was 12.7 years (interquartile range 11.5–14.4) and diabetes duration 6.5 years (4.1–9.3) at first assessment, and median follow-up was 6.2 years (range 1–15.3).

RESULTS— The incidence of persistent microalbuminuria was 4.6 (95% CI 3.3–6.1) per 1,000 patient-years. Predictors of persistent microalbuminuria from the first assessment using multiple logistic regression were high cholesterol (odds ratio 2.2 [95% CI 1.2–4.0]) and borderline microalbuminuria (2.5 [1.2–5.2]). Predictors using Cox regression were HbA1c (hazard ratio 1.4 [95% CI 1.1–1.7]), age at diagnosis (1.2 [1.1–1.3]), obesity (3.6 [0.8–15.5]), and insulin dose (2.7 [1.0–7.5]).

CONCLUSIONS— Children and adolescents with type 1 diabetes who have borderline microalbuminuria are more than twice as likely to develop persistent microalbuminuria. In addition to poor glycemic control, clinical markers of insulin resistance were associated with an increased risk of microalbuminuria.

Microalbuminuria is well recognized as a risk factor for the development of diabetic nephropathy in adults, but its natural history is less clear in children and adolescents. Within 2 decades of diabetes onset, a single episode of microalbuminuria is found in 2–18% of children and adolescents with type 1 diabetes (13) but may be transient in up to half of cases (4,5). Established risk factors for microalbuminuria in adolescents and adults include duration of diabetes (5,6), suboptimal glycemic control (7,8), hypertension, and smoking (9).

Markers of insulin resistance have been associated with the development of microalbuminuria in adults with type 1 diabetes (1014), although there is less evidence for this in children and adolescents. Of note, however, the incidence of microalbuminuria in type 1 diabetes increases at puberty (8), a time of exaggerated physiological insulin resistance (1517). Indeed, higher androgens and growth hormone have been found in adolescents with type 1 diabetes in association with higher albumin excretion (18,19), while the effects of higher BMI and other features of the metabolic syndrome on the risk of microalbuminuria in this age-group are unclear.

The aims of this 15-year longitudinal study were to identify risk factors for early nephropathy and to explore the potential role of insulin resistance in the development of persistent microalbuminuria. We examined putative risk factors at initial assessment for the subsequent development of persistent microalbuminuria and used survival analysis to evaluate risk factors over time.

Children and adolescents with type 1 diabetes attending complications assessment at The Children’s Hospital at Westmead during 1989–2004 were included in this retrospective cohort study. Patients were screened according to established guidelines, which recommend annual assessment beginning 5 years after diagnosis in prepubertal children and 2 years after diagnosis in pubertal children (20,21). Complications assessment was undertaken during a 2-h visit that consisted of clinical assessment by the endocrinologist; anthropometry, blood pressure measurement, and pubertal staging; screening for retinopathy, microalbuminuria, and neuropathy; and HbA1c (A1C) and biochemistry, as previously described (3). Patients were included in this study if albumin excretion rate (AER) had been measured two or more times, spaced at least 12 months apart. Complications assessment results from all visits were included in the analyses. Patients and their families gave informed consent for the results of the complications assessment to be analyzed. Approval was obtained by the Ethics Committee of the Children’s Hospital at Westmead.

Three timed overnight urine specimens were collected immediately before the complications assessment. Urinary albumin was measured using a polyclonal radioimmunoassay (Pharmacia RIA, Beckman Coulter, Australia) from 1990 to March 2000. From April 2000, the laboratory changed to nephelometric assay using the IMMAGE analyzer (IMMAGE = [0.8734 × radioimmunoassay value] − 0.501, r = 0.99). Microalbuminuria was defined as an AER of 20–200 μg/min in at least two of three samples, and if present, repeat collections were requested 3 months later. Microalbuminuria was further classified as transient if it reverted to the normoalbuminuria range within 12 months and persistent if AER remained >20 μg/min for >12 months. Normoalbuminuria was defined as mean AER <7.5 μg/min in all urine samples collected. This cutoff approximates the 95th percentile for healthy children (22). Borderline microalbuminuria was defined as mean AER between 7.5 and 20 μg/min.

Retinopathy was assessed by seven-field fundal photography and graded according to the modified Airlie House Classification (23). Retinopathy was defined as at least one microaneurysm and one hemorrhage.

Height was measured using a Harpenden stadiometer (Holtain, Crymmych, U.K.) and weight using electronic scales. Obesity was defined as a BMI SD score ≥2 (24). Blood pressure was measured by auscultation after 5 min of rest, and percentiles were calculated based on age and sex (25).

At each complications assessment, glycemic control was assessed by glycated hemoglobin (GHb) calorimetrically (26) before February 1994 and subsequently by A1C using high-performance liquid chromatography (Diamat Bio-Rad; normal range 4–6%). GHb values were converted to A1C (Diamat = 1.9088 + 0.0043 × GHb, r = 0.92). The interassay coefficients of variation (CVs) were 1.1 and 1.2% for an A1C of 5.95 and 9.76%, respectively.

Biochemical markers of insulin resistance were assessed in a subgroup of 161 patients (73 males) with stored serum samples (24 with microalbuminuria and 137 with normoalbuminuria). IGF-I, sex hormone–binding globulin (SHBG), testosterone, and dehydroepiandrosterone sulfate (DHEAS) were measured using a solid-phase chemiluminescent immunometric assay (Immulite; DPC, Los Angeles, CA). Interassay CVs were 3.7% for IGF-I, 4.2% for SHBG, 6.5% for DHEAS, and 7.8% for testosterone.

Statistical analysis

Descriptive statistics are presented as mean (±SD) score for normally distributed data and median (interquartile range or range) for skewed data. DHEAS, IGF-I, SHBG, and free androgen index were compared in individuals with and without microalbuminuria by Mann-WhitneyU tests.

Baseline risk factors

Early risk factors for the development of persistent microalbuminuria from the first ever complications assessment were examined using logistic regression. Patients who subsequently developed persistent microalbuminuria (defined as “case subjects”) were compared with1) all other patients (labeled “others” in Table 1) and2) only those who continued to have normoalbuminuria (that is, patients with borderline microalbuminuria and transient microalbuminuria were excluded to avoid misclassification bias). Potential explanatory variables from the first ever complications assessment used in the regression models were BMI, blood pressure percentile, cholesterol, insulin dose, multiple injections (defined as three or more insulin injections per day), and A1C. Hypercholesterolemia was defined as a serum cholesterol >5.2 mmol/l (27). Clinically relevant interaction terms were examined; models were assessed for goodness of fit and compared using likelihood ratio tests.

Survival analysis

Cox proportional hazards regression analysis was used to account for differences in duration of follow-up. Duration of diabetes was used as the time varying coordinate, with development of persistent microalbuminuria as the outcome. The same explanatory variables were examined with all available time points included in the models. Statistical analysis was performed using Stata (version 8; StataCorp, College Station, TX).

In the entire cohort (n = 991) at first assessment, median age was 12.7 years (interquartile range 11.5–14.4) and duration of diabetes was 6.5 years (4.1–9.3). The median duration of follow-up after the first complication assessment was 6.2 years (range 1.0–15.3), and the median number of assessments with AER measurements available was four per patient (range 2–12). Characteristics of patients with and without microalbuminuria are shown in Table 1.

Natural history

There was a progressive increase in AER in the years before the onset of persistent microalbuminuria (Fig. 1). At first assessment, microalbuminuria was found in 40 patients (4%) and borderline microalbuminuria in 184 (19%), and the remaining 767 had normoalbuminuria. Of those with normoalbuminuria at first assessment, 492 (64%) continued to have normoalbuminuria during follow-up, 212 (28%) had an episode of borderline microalbuminuria, and 59 (8%) had an episode of microalbuminuria. In total, 436 (44%) had an episode of borderline microalbuminuria at any time point; of these, 343 reverted to normoalbuminuria, 33 persisted as borderline microalbuminuria, and 60 progressed to microalbuminuria. Overall, 124 (12.4%) patients had an episode of microalbuminuria, 60 were transient, 45 were persistent, and 19 could not be classified because of insufficient follow-up information (and were excluded from further analysis, leaving 972 patients). None of the patients with transient microalbuminuria had been treated with ACE inhibitors.

The incidence of persistent microalbuminuria was 4.6 per 1,000 patient-years (95% CI 3.3–6.1). The median diabetes duration at the onset of persistent microalbuminuria was 9.3 years, and the earliest case was 1.6 years after diagnosis of diabetes. Six patients, all with preexisting microalbuminuria, developed macroalbuminuria. The median diabetes duration at the onset of macroalbuminuria was 11.5 years.

Baseline risk factors

Compared with all others, patients who subsequently developed persistent microalbuminuria were significantly more likely to have borderline microalbuminuria or microalbuminuria, hypercholesterolemia, blood pressure >95th percentile, obesity, and longer diabetes duration at the first complications assessment. In multivariate analysis, baseline borderline microalbuminuria, microalbuminuria, and hypercholesterolemia remained significant predictors of subsequent persistent microalbuminuria. When those with transient microalbuminuria or borderline microalbuminuria were excluded from the analysis, duration and glycemic control were the only significant variables in the multivariate model (Table 1).

Survival analysis

In Cox proportional hazards regression, higher A1C, older age at diagnosis, higher insulin dose, and obesity were predictive of the development of persistent microalbuminuria (Table 2).

Biochemical subanalysis

Patients with persistent microalbuminuria were older than patients with normoalbuminuria (17.4 vs. 16.0 years, respectively; P = 0.04) and their A1C was higher (9.1 vs. 8.3%, P = 0.02) but did not differ with regard to diabetes duration (10.2 vs. 10.3 years,P = 0.9) or BMI SD score (0.78 vs. 0.69,P = 0.7). DHEAS was significantly higher in patients with persistent microalbuminuria: 5.3 μmol/l (range 2.2–11.2) vs. 3.9 (0.4–15.8) (P = 0.02), and SHBG was significantly lower in females with persistent microalbuminuria (3.2 vs. 323.5 nmol/l,P = 0.03) but not males (35.0 vs. 52.1). There were no significant differences in serum IGF-I, testosterone, and free androgen index between the two groups overall and when stratified for sex.

In this longitudinal study of 972 youth with type 1 diabetes, the incidence of persistent microalbuminuria was 4.6 per 1,000 patient-years. Early elevation of AER at first complication assessment was a significant risk factor for the later development of persistent microalbuminuria, and there was a gradual rise in AER before the diagnosis. The modifiable risk factors identified for persistent microalbuminuria were hypercholesterolemia and glycemic control, in addition to the recognized risk factors of older age and duration. Markers of insulin resistance such as higher BMI, DHEAS, and higher insulin dose were also identified as predictors but did not remain significant in multivariate analysis, possibly because of our low rate of persistent microalbuminuria, despite the large cohort.

The main strengths of this study are its longitudinal nature and the number of patients followed over time. Although not population based, this cohort has similar characteristics to our previous population-based studies (28), and the long period of follow-up provides important information on natural history in a typical clinic population. Misclassification bias has been minimized by defining persistent microalbuminuria as being present on two occasions separated by at least 12 months. Despite the broad nature of the study population, there remains a possibility of sampling bias that may work to either inflate or deflate the reported incidence. Both patients more concerned about their health and risk of complications and patients with more risk factors for complications may be more likely to present for complication assessment. Although followed for up to 15 years, the study is underpowered because of the low incidence of persistent microalbuminuria. Sample size calculations indicate that more cases (at least 70) are needed to achieve adequate power for markers of insulin resistance that were significant in univariate analysis.

Borderline microalbuminuria at first complication assessment more than doubled the risk of persistent microalbuminuria compared with normoalbuminuria, and the effect persisted after adjusting for duration. This confirms previous studies in which early elevation of AER and the rate of rise of albumin-to-creatinine ratio within the normal range were predictors for microalbuminuria (8,29). While this could be explained by genetic predisposition to nephropathy (3032), it argues for the possibility of intervention at a lower level of albuminuria than current guidelines recommended for adolescents (21).

Increasing age at diagnosis increased the risk of microalbuminuria in longitudinal analysis. Certainly, increasing duration of diabetes increases the risk of complications, but the use of survival analysis allowed age to be examined as an independent predictor of microalbuminuria. Although there are inconsistencies in the available literature in relation to the reported effects of prepubertal years of diabetes complications, often due to methodological differences (5,6,33), we have previously reported the risk for retinopathy and microalbuminuria increases as the child approaches the clinical onset of gonadarche (6). Furthermore, in the subgroup in which androgens were measured, DHEAS was higher in individuals with persistent microalbuminuria, who were also older.

Markers of insulin resistance, including hypercholesterolemia, adiposity as measured by BMI, higher insulin dose, and higher androgens, were associated with the development of persistent microalbuminuria. Insulin resistance without diabetes has been linked to microalbuminuria in adults (34), and elevation of AER may begin in childhood in association with obesity and other features of the metabolic syndrome (35). This is particularly relevant considering the epidemic of obesity seen among children and adolescents in developed countries (36,37), and those with type 1 diabetes are not immune (38). In addition, insulin omission in type 1 diabetes can cause the same clinical features as seen in insulin resistance, that is, high reported insulin requirement, elevated cholesterol, triglycerides and free fatty acids, and hepatic steatosis. Furthermore, there are interactive relationships between insulin dose, glycemic control, and BMI SD score. Although insulin dose is a marker of insulin resistance (39,40), it also varies with carbohydrate consumption, physical activity (which we did not measure), insulin type, and regimen and can be misreported, particularly in noncompliant adolescents.

This study indicates that individuals with borderline microalbuminuria need to be followed closely, since they are at increased risk of developing microalbuminuria. The transient nature of microalbuminuria in children and adolescents would suggest the need for at least 12 months of documented microalbuminuria before treatment is considered. Identifying young people most at risk of nephropathy is important to allow timely and appropriate intervention. There is good evidence in adults that ACE inhibitors and angiotensin II blockers are useful in the prevention of diabetic nephropathy (41), as is optimizing glycemic control. Our study also suggests preventative strategies should address insulin resistance in young people with type 1 diabetes.

1.
Svensson M, Sundkvist G, Arnqvist H, Bjork E, Blohme G, Bolinder J, Henricsson M, Nystrom L, Torffvit O, Waernbaum I, Ostman J, Erikkson JW: Signs of nephropathy may occur early in young adults with diabetes despite modern diabetes management.
Diabetes Care
26
:
2903
–2909,
2003
2.
Donaghue KC, Fairfield JM, Chan A, Hing SJ, Howard NJ, Silink M: Diabetes complications screening in 937 children and adolescents.
J Pediatr Endocrinol Metab
12
:
185
–192,
1999
3.
Mohsin F, Craig ME, Cusamano J, Chan AK, Hing SJ, Lee JW, Silink M, Howard NJ, Donaghue KC: Discordant trends in microvascular complications in adolescents with type 1 diabetes from 1990–2002.
Diabetes Care
28
:
1974
–1980,
2005
4.
Gorman D, Sochett E, Daneman D: The natural history of microalbuminuria in adolescents with type 1 diabetes.
J Pediatr
134
:
333
–337,
1999
5.
Schultz CJ, Konopelska-Bahu T, Dalton RN, Carroll TA, Stratton I, Gale EA, Neil A, Dunger DB: Microalbuminuria prevalence varies with age, sex, and puberty in children with type 1 diabetes followed from diagnosis in a longitudinal study.
Diabetes Care
22
:
495
–502,
1999
6.
Donaghue KC, Fairchild JM, Craig ME, Chan AK, Hing S, Cutler LR, Howard NJ, Silink M: Do all prepubertal years of diabetes duration contribute equally to diabetes complications?
Diabetes Care
26
:
1224
–1229,
2003
7.
Diabetes Control and Complications Trial Research Group: Effect of intensive diabetes treatment on the development and progression of long-term complications in adolescents with insulin-dependent diabetes mellitus: Diabetes Control and Complications Trial.
J Pediatr
125
:
177
–188,
1994
8.
Couper JJ, Clarke CF, Byrne GC, Jones TW, Donaghue KC, Nairn J, Boyce D, Russell M, Stephens M, Raymond J, Bates DJ, McCaul K: Progression of borderline increases in albuminuria in adolescents with insulin-dependent diabetes mellitus.
Diabet Med
14
:
766
–771,
1997
9.
Rossing P, Hougaard P, Parving H-H: Risk factors for development of incipient and overt nephropathy in type 1 diabetic patients.
Diabetes Care
25
:
859
–864,
2002
10.
Zenere B, Arcaro G, Saggiani F, Rossi L, Muggeo M, Lechi A: Noninvasive detection of functional alterations of the arterial wall in IDDM patients with and without microalbuminuria.
Diabetes Care
18
:
975
–981,
1995
11.
Yip J, Mattock MB, Morocutti A, Sethi M, Trevisan R, Viberti G: Insulin resistance in insulin-dependent diabetic patients with microalbuminuria.
Lancet
342
:
883
–887,
1993
12.
Stenhouwer C, Fischer H, van Huijk A, Polack B, Donker A: Endothelial dysfunction precedes development of microalbuminuria in IDDM.
Diabetes
44
:
561
–564,
1995
13.
Ekstrand A, Groop P, Gronhagen-Riska C: Insulin resistance precedes microalbuminuria in patients with insulin-dependent diabetes mellitus.
Nephrol Dial Transplant
13
:
3079
–3083,
1998
14.
Orchard T, Chang Y, Ferrell R, Petro N, Ellis D: Nephropathy in type 1 diabetes: a manifestation of insulin resistance and multiple genetic susceptibilities.
Kidney Int
62
:
963
–970,
2002
15.
Moran A, Jacobs D, Steinberger J, Hong C, Prineas R, Luepker R, Sinaiko A: Insulin resistance during puberty.
Diabetes
48
:
2039
–2044,
1999
16.
Bloch C, Clemond P, Sperling M: Puberty decreases insulin sensitivity.
J Pediatr
110
:
481
–487,
1987
17.
Travers S, Jeffers B, Bloch C, Hill J, Eckel R: Gender and Tanner stage differences in body composition and insulin sensitivity in early pubertal children.
J Clin Endocrinol Metab
80
:
172
–178,
1995
18.
Amin R, Schultz C, Ong K, Frystyk J, Dalton R, Perry L, Oskov H, Dunger D: Low IGF-1 and elevated testosterone during puberty in subjects with type 1 diabetes developing microalbuminuria in comparison to normoalbuminuric control subjects.
Diabetes Care
26
:
1456
–1471,
2003
19.
Amin R, Williams R, Frystyk J, Umpleby M, Matthews D, Orskov H, Dalton R, Dunger D: Increasing urine albumin excretion is associated with growth hormone hypersecretion and reduced clearance of insulin in adolescents and young adults with type 1 diabetes.
Clin Endocrinol (Oxf)
62
:
137
–144,
2005
20.
Australasian Paediatric Endocrine Group:
APEG Handbook on Childhood and Adolescent Diabetes: The Management of Insulin-Dependent (Type 1) Diabetes (IDDM)
. Sydney, NSW Govt. Printing Office,
1996
21.
International Society of Paediatric and Adolescent Diabetes:
Consensus Guidelines for Management of Insulin Dependent (Type 1 Diabetes) in Childhood and Adolescence.
Zeist, the Netherlands, Medical Forum International,
2000
22.
Couper JJ, Staples AJ, Cocciolone R, Nairn J, Badcock N, Henning P: Relationship of smoking and albuminuria in children with insulin-dependent diabetes.
Diabet Med
11
:
666
–669,
1994
23.
Group DRSR: Report 7.a: Modification of the Airlie house classification of diabetic retinopathy.
Invest Ophthalmol Vis Sci
21
:
210
–226,
1981
24.
Cole TJ: The LMS method for constructing normalized growth.
Eur J Clin Nutr
44
:
45
–60,
1990
25.
National Heart, Lung, and Blood Institute: Report of the Second Task Force on Blood Pressure Control in Children–1987: Task Force on Blood Pressure Control in Children.
Pediatrics
79
:
1
–25,
1987
26.
Eross J, Kreutzmann D, Jimenez M, Keen R, Rogers S, Cowell C: Colorimetric measurement of glycosylated protein in whole blood, red blood cells, plasma and dried blood.
Ann Clin Biochem
21
:
477
–483,
1984
27.
American Academy of Pediatrics, Committee on Nutrition: Cholesterol in children.
Pediatrics
101
:
141
–147,
1998
28.
Donaghue KC, Craig ME, Chan AK, Fairchild J, Cusumano J, Verge C, Crock P, Hing S, Howard N, Silink M: Prevalence of diabetes complications six years after diagnosis in an incident cohort of childhood diabetes.
Diabet Med
22
:
711
–718,
2005
29.
Schultz CJ, Neil HA, Dalton RN, Dunger DB: Risk of nephropathy can be detected before the onset of microalbuminuria during the early years after diagnosis in type 1 diabetes.
Diabetes Care
23
:
1811
–1825,
2000
30.
Krolewski A: Genetics of diabetic nephropathy: evidence of major and minor gene effects.
Kidney Int
55
:
1582
–1596,
1999
31.
De Cosmo S, Argiolas A, Miscio G: A PC-1 amino acid variant (K121Q) is associated with faster progression of renal disease in patients with type 1 diabetes and albuminuria.
Diabetes
49
:
521
–524,
2000
32.
Marre M, Bernadet P, Gallois Y: Relationships between angiotensin I-converting enzyme gene polymorphism, plasma levels, and diabetic retinal and renal complications.
Diabetes
43
:
384
–388,
1994
33.
Svensson M, Erikson J, Dahlquist G: Early glycaemic control, age of onset, and development of microvascular complications in childhood-onset type 1 diabetes.
Diabetes Care
27
:
955
–962,
2004
34.
Kim Y, Kim C-H, Choi C, Chung Y, Lee M, Lee S, Park J, Hong S, Lee K-U: Microalbuminuria is associated with the insulin resistance syndrome independent of type 2 diabetes in the Korean population.
Diabetes Res Clin Pract
52
:
145
–152,
2001
35.
Csernus K, Lanyi E, Erhardt E, Molnar D: Effect of childhood obesity and obesity-related cardiovascular risk factors on glomerular and tubular protein excretion.
Eur J Pediatr
164
:
44
–49,
2005
36.
Booth M, Wake M, Armstrong T: The epidemiology of overweight and obesity among Australian children and adolescents, 1995–1997.
Aust N Z J Public Health
25
:
162
–169,
2001
37.
Ogden C, Flegal K, Carroll M, Johnson C: Prevalence and trends in overweight among children and adolescents, 1999–2000.
JAMA
288
:
1728
–1732,
2002
38.
Lidman I, Pietropaolo M, Arslanian S, La Porte R, Becker D: Changing prevalence of overweight children and adolescents at onset of insulin treated diabetes.
Diabetes Care
26
:
2871
–2875,
2003
39.
Yki-Jarvinen H, Koivisto V: Natural course of insulin resistance in type 1 diabetes.
N Engl J Med
315
:
224
–229,
1986
40.
Kruszynska YT, Home PD: Insulin insensitivity in type 1 diabetes.
Diabet Med
4
:
414
–422,
1987
41.
Strippoli GF, Craig ME, Deeks JJ, Schena FP, Craig JC: Effects of angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists on mortality and renal outcomes in diabetic nephropathy: systematic review.
BMJ
329
:
828
,
2004

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