Introduction
The global incidence of diabetes mellitus among children and adolescents has risen substantially over the past two decades, and this increase is no longer confined to type 1 diabetes mellitus (T1DM). Data from the SEARCH for Diabetes in Youth study and related registries indicate that although T1DM remains the predominant form of pediatric diabetes, the incidence of youth-onset type 2 diabetes mellitus (T2DM) has increased disproportionately. This increase has been particularly pronounced among adolescents from racial and ethnic minority groups and socioeconomically disadvantaged backgrounds and has closely paralleled rising rates of childhood obesity [1-3]. A recent Lancet series characterized early-onset T2DM as “the next major diabetes transition,” emphasizing that this phenotype is not merely an earlier presentation of adult-onset disease but a biologically distinct and more aggressive condition with a disproportionate impact on the kidneys [4-6].
Diabetic kidney disease (DKD) is among the most consequential long-term complications of diabetes and contributes substantially to premature cardiovascular disease, dialysis dependence, and mortality among adults who developed diabetes during childhood [7-9]. For decades, clinical attention to renal complications in pediatric diabetes focused almost exclusively on T1DM because of its historical predominance and the well-characterized natural history established by the Diabetes Control and Complications Trial (DCCT) and its long-term follow-up study, the Epidemiology of Diabetes Interventions and Complications (EDIC) [10,11]. However, subclinical renal injury—manifesting as glomerular hyperfiltration, increased urinary albumin excretion, and early elevations in blood pressure—can occur within the first decade after diagnosis in both forms of diabetes, well before any decline in estimated glomerular filtration rate (eGFR) becomes apparent [12,13]. The pathophysiology of early renal injury differs meaningfully between T1DM and T2DM. In T1DM, hyperglycemia affects kidneys that, at least initially, are not burdened by insulin resistance or excess adiposity. Renal hemodynamic changes, including afferent arteriolar vasodilation, increased glomerular hydrostatic pressure, and hyperfiltration, are driven predominantly by glycemic exposure, abnormalities in tubuloglomerular feedback, and activation of the renin–angiotensin–aldosterone system (RAAS) [7,14]. Conversely, in T2DM, these hemodynamic abnormalities occur against a background of insulin resistance, visceral adiposity, dyslipidemia, hyperuricemia, and chronic low-grade inflammation, all of which independently promote glomerular hypertrophy, podocyte stress, and tubulointerstitial injury [15-17].
Large prospective cohorts have begun to quantify the extent to which these trajectories diverge. The Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study and its long-term extension, TODAY2, demonstrated that elevated blood pressure and microalbuminuria develop within a few years after T2DM diagnosis in a substantial proportion of adolescents. By their mid-20s, more than half of these individuals had evidence of DKD [18-20]. In comparison, large T1DM registries and the SEARCH study indicate a slower, although still clinically important, accumulation of renal injury during the first decade after diagnosis [21-23]. Direct head-to-head comparisons of T1DM and T2DM in youth remain relatively scarce, and the contributions of glycemic control, adiposity, sex, puberty, and genetic background to these divergent trajectories remain incompletely understood. Given the rising global burden of both T1DM and T2DM among youth, the long interval between subclinical renal injury and clinically apparent DKD, and the increasing availability of renoprotective therapies that may be most effective when initiated early, a focused synthesis of comparative evidence on early renal injury in youth-onset T1DM and T2DM is timely.
Therefore, this review aims to consolidate the available evidence regarding the prevalence, timing, and mechanisms of early renal injury in these populations and translate these findings into a framework for surveillance and early intervention in routine pediatric endocrinology and nephrology practice.
Objectives
This review has three interrelated objectives: (1) to compare the prevalence, age at onset, and trajectories of early markers of renal injury (including microalbuminuria, hypertension, glomerular hyperfiltration, and changes in eGFR) between individuals with youth-onset T1DM and T2DM, drawing on cohorts such as TODAY/TODAY2, SEARCH for Diabetes in Youth, and the Adolescent Type 1 Diabetes Cardio-Renal Intervention Trial (AdDIT); (2) to examine the pathophysiological mechanisms that may explain the earlier onset and more rapid progression of renal injury in T2DM, including the roles of hyperglycemia, insulin resistance, visceral adiposity, dyslipidemia, hyperuricemia, inflammation, sex, and puberty; and (3) to summarize the evidence regarding renoprotective interventions (including intensive glycemic control, RAAS blockade, sodium–glucose cotransporter 2 [SGLT2] inhibitors, glucagon-like peptide-1 [GLP-1] receptor agonists, metformin, and metabolic/bariatric surgery) as well as the prognostic implications of early renal injury for long-term kidney and cardiovascular outcomes in both groups.
Methods
Review type and reporting framework
This narrative review was designed to synthesize and contextualize evidence comparing early renal injury in youth-onset T1DM and T2DM rather than to provide pooled quantitative estimates of effect. Therefore, formal adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was not required. Nevertheless, to enhance the transparency of the literature-selection process, a PRISMA-style flow diagram illustrating the identification, screening, and inclusion of references is provided in Fig. 1.
Search strategy and sources
A structured search of PubMed/MEDLINE was conducted to identify English-language, PubMed-indexed publications published between January 2001 and May 2026. The search combined controlled vocabulary and free-text terms related to “type 1 diabetes,” “type 2 diabetes,” “children,” “adolescents,” “youth-onset,” “diabetic kidney disease,” “diabetic nephropathy,” “albuminuria,” “microalbuminuria,” “hyperfiltration,” “glomerular filtration rate,” “hypertension,” and “chronic kidney disease.” The reference lists of relevant reviews and major cohort publications were manually searched to identify additional primary studies. Key landmark trials and cohorts, including TODAY/TODAY2, SEARCH for Diabetes in Youth, AdDIT, Adolescent Type 1 Diabetes Treatment with SGLT2i for Hyperglycemia and Hyperfiltration Trial (ATTEMPT), Diabetes Study of Linagliptin and Empagliflozin in Children and Adolescents (DINAMO), Evaluation of Liraglutide in Pediatrics with Diabetes (Ellipse), DCCT/EDIC, and Restoring Insulin Secretion (RISE), were specifically sought because of their relevance to the review topic.
Inclusion criteria
Studies were eligible for inclusion if they (1) enrolled children, adolescents, or young adults (generally aged <25 years at diagnosis or assessment) with T1DM or T2DM; (2) evaluated at least one marker of early renal injury, including urinary albumin excretion or albuminuria, blood pressure or hypertension, eGFR or measured GFR (mGFR), hyperfiltration, or validated tubular or renal biomarkers; (3) were published in a PubMed-indexed, peer-reviewed journal within the past 25 years, although a small number of older foundational studies, such as the original report on the pediatric DCCT cohort, were retained for historical context when directly relevant; and (4) provided sufficient methodological detail to permit assessment of the study design and quality.
Exclusion criteria
Studies were excluded if they (1) exclusively enrolled populations with adult-onset diabetes and did not report data for a distinguishable pediatric or adolescent subgroup; (2) were case reports, conference abstracts without corresponding full-text publications, editorials without original data, or non-peer-reviewed sources; (3) focused exclusively on nonrenal complications, such as retinopathy or neuropathy, without reporting renal outcomes; or (4) could not be verified as PubMed-indexed publications with confirmed PubMed identifiers.
Quality and risk of bias assessment
Given the predominance of observational cohort data in this field, the Newcastle–Ottawa Scale (NOS) framework was used informally to appraise the selection, comparability, and outcome-assessment domains of the major observational studies and registries cited (e.g., TODAY, TODAY2, SEARCH, and large national T1DM registries). For randomized controlled trials (RCTs) (AdDIT, ATTEMPT, DINAMO, and Ellipse), the domains of the Cochrane Risk of Bias 2 (RoB 2) tool (bias arising from the randomization process, deviations from intended interventions, missing outcome data, outcome measurement, and selective reporting) were used as a qualitative checklist to contextualize the strength of the evidence presented in Tables 1 and 2. Studies with major unresolved concerns in more than one RoB 2 domain or considered to have a high overall NOS-equivalent risk of bias were either excluded or explicitly identified as providing lower-certainty evidence in the narrative synthesis.
Data extraction and synthesis
For each included study, the following data were extracted, where available: study design, sample size, diabetes type and duration, participant age and pubertal status, definitions and thresholds for albuminuria, hypertension, and hyperfiltration, the eGFR equation used, follow-up duration, and key renal outcome estimates, including prevalence, incidence, hazard ratios, and trajectory slopes. Because the included studies varied substantially in their designs, populations, and outcome definitions, a formal meta-analysis was not performed. Instead, the findings were synthesized narratively and organized into comparative summary tables (Tables 1-4) to facilitate direct comparison between T1DM and T2DM.
Definitions of renal injury markers
Because the included studies used varying thresholds, the following conventions were applied when interpreting findings throughout this review unless study-specific definitions are stated in the text or tables: microalbuminuria was defined as a urinary albumin-to-creatinine ratio of approximately 30–300 mg/g (3.4–34 mg/mmol) or an overnight or timed urinary albumin excretion rate of 20–200 µg/min, consistent with International Society for Pediatric and Adolescent Diabetes criteria; hypertension was defined as systolic and/or diastolic blood pressure at or above the 95th percentile for age, sex, and height in children or at or above 130/80 mmHg in older adolescents and young adults; glomerular hyperfiltration was defined as an eGFR or mGFR exceeding approximately 135–140 mL/min/1.73 m2, consistent with the thresholds used in the TODAY, Improving Renal Complications in Adolescents with Type 2 Diabetes through REsearch (iCARE), and SEARCH cohorts; and eGFR decline was defined as an annualized decrease exceeding a study-specified threshold, most commonly ≥3 mL/min/1.73 m2 per year, as used in the SEARCH eGFR substudy.
Results
A total of 39 PubMed-indexed publications met the inclusion criteria and formed the evidence base for this review (Fig. 1). These included large prospective cohort studies (e.g., TODAY/TODAY2, SEARCH for Diabetes in Youth, the Oxford and DCCT/EDIC pediatric cohorts, and national T1DM registries), RCTs (AdDIT, ATTEMPT, DINAMO, and Ellipse), narrative and systematic reviews, and mechanistic and biomarker studies. The findings are summarized in four comparative tables.
Key comparative markers of early renal injury in the two types of diabetes are summarized in Table 3. Across all domains examined, markers of early renal injury are detectable in both forms of youth-onset diabetes; however, they emerge earlier, occur more frequently, and progress more rapidly in T2DM. The TODAY/TODAY2 findings are particularly striking, demonstrating that within approximately 4–13 years after diagnosis, adolescents with T2DM accumulate a burden of albuminuria, hypertension, and overt DKD that takes considerably longer to develop and remains less prevalent in those with T1DM.
The major pediatric cohort studies and RCTs informing this evidence base are summarized in Table 1. The evidence is derived predominantly from a small number of large, well-conducted cohorts and trials, most notably TODAY/TODAY2 for T2DM and SEARCH and DCCT/EDIC for T1DM. Direct, contemporaneous, head-to-head comparisons of the two types of diabetes within a single study, such as the SEARCH analysis of eGFR trajectories, remain relatively uncommon. Nevertheless, such comparisons are particularly informative because they account for many shared environmental and ascertainment factors.
The principal pathophysiological mechanisms and candidate early biomarkers are compared in Table 4, and the mechanistic cascade is illustrated in Fig. 2. The available evidence indicates that early renal injury in T1DM is driven largely by a relatively circumscribed set of hyperglycemia-related hemodynamic and inflammatory mechanisms. Conversely, renal injury in T2DM reflects the convergence of these pathways with insulin resistance, obesity, atherogenic dyslipidemia, hyperuricemia, and increased inflammation. This “multiple-hit” model plausibly explains the earlier onset and more rapid clinical progression of renal injury in T2DM.
Evidence-based renoprotective interventions are summarized in Table 2. Although the evidence regarding renoprotective interventions in youth-onset T1DM and T2DM has expanded considerably in recent years, particularly following the publication of the ATTEMPT and DINAMO trials, most studies remain relatively small and have limited follow-up durations. Furthermore, few have evaluated hard renal outcomes, such as progression to stage 3 chronic kidney disease or beyond. Nevertheless, the consistent direction of effects observed with RAAS blockade, SGLT2 inhibition, GLP-1 receptor agonism, and metabolic surgery supports a multipronged approach to early renal protection tailored to the predominant pathophysiological drivers of each type of diabetes.
Discussion
This review compared the prevalence, timing, and trajectories of albuminuria, hypertension, hyperfiltration, and changes in eGFR between youth-onset T1DM and T2DM. As this was a narrative rather than a systematic review, no formal meta-analysis was performed. Quantitative estimates were reproduced as originally published and interpreted qualitatively rather than statistically pooled.
The most striking finding was the rapid onset of microalbuminuria in T2DM. In the TODAY cohort, the prevalence of microalbuminuria more than doubled, increasing from 6.3% to 16.6% over a mean follow-up of only 3.9 years [18]. Conversely, comparable increases in the prevalence of microalbuminuria in large T1DM registries typically occur over a diabetes duration of 10–15 years [21]. This difference cannot be explained by age alone because TODAY participants were, if anything, slightly older at diagnosis than individuals with the typical age of T1DM onset. Instead, it suggests that renal injury accumulates at a fundamentally different rate relative to diabetes duration in T2DM. Patterns of glomerular hyperfiltration and eGFR trajectories reinforce this interpretation. The SEARCH for Diabetes in Youth eGFR substudy provides perhaps the clearest available head-to-head comparison. Among participants followed for at least a decade, an increase in eGFR consistent with hyperfiltration occurred in 15.6% of those with T2DM compared with only 2.8% of those with T1DM, whereas eGFR decline occurred in 18.1% of the T2DM group and 23.8% of the T1DM group [22]. The higher frequency of eGFR decline among participants with T1DM in this analysis may partly reflect their longer mean follow-up and older age at the end of the observation period. However, the markedly higher frequency of early hyperfiltration in T2DM is consistent with findings from the iCARE study, in which the baseline mGFR in adolescents with obesity and T2DM frequently exceeded 120 mL/min/1.73 m2—a level rarely observed after an equivalent duration of T1DM [12,34].
Hypertension is a third closely related marker of early renal injury, and the TODAY findings are again instructive. The prevalence of hypertension increased from 11.6% to 33.8% within approximately 4 years after T2DM diagnosis and continued to rise through young adulthood in TODAY2 [18,19]. This rapid increase likely reflects both the direct hemodynamic effects associated with hyperfiltration, including increased intraglomerular pressure and activation of the RAAS, and the independent contributions of obesity-related sympathetic activation and sodium retention. The latter mechanisms are generally less prominent in lean adolescents at the time of T1DM diagnosis [7,14]. International consensus guidelines now explicitly recognize hypertension as both an early marker and an independent accelerator of DKD in youth, underscoring the importance of routine blood pressure measurement from the time of diabetes diagnosis in both groups [33].
Taken together, the evidence reviewed under the first objective supports a coherent conclusion: early renal injury occurs in both youth-onset T1DM and T2DM, but its progression is accelerated in T2DM. The TODAY2 finding that 54.8% of participants had developed DKD by a mean age of approximately 26 years and after a mean diabetes duration of approximately 13 years contrasts markedly with the cumulative nephropathy prevalence of approximately 20%–25% reported in T1DM cohorts followed for a similar or longer duration [11,19,21]. This approximately twofold difference in cumulative disease burden over a comparable or shorter period is the central empirical observation that the remainder of this discussion seeks to explain mechanistically and address therapeutically.
The mechanisms underlying these divergent trajectories differ between the two types of diabetes. In T1DM, the predominant early mechanism is hyperglycemia-driven renal hemodynamic adaptation. Chronic hyperglycemia increases proximal tubular glucose and sodium reabsorption, thereby reducing sodium delivery to the macula densa, triggering tubuloglomerular feedback-mediated afferent arteriolar vasodilation, and increasing glomerular hydrostatic pressure and single-nephron GFR [14]. This process is closely related to cumulative glycemic exposure, which may explain why intensive glycemic control in the pediatric DCCT cohort reduced the subsequent risk of microalbuminuria. This benefit persisted for years after the intensive treatment period ended, reflecting the so-called “metabolic memory” effect documented during the EDIC follow-up of the same cohort [10,11]. Importantly, among adolescents with T1DM who are not overweight, these hemodynamic changes occur without the additional renal burden associated with excess adiposity and insulin resistance, which may partly explain the comparatively slower accumulation of renal injury.
Conversely, in T2DM, the same hyperglycemia-driven hemodynamic mechanisms operate against a fundamentally different metabolic background. This distinction underpins the central proposition of the second objective: early renal injury in youth-onset T2DM reflects a “multiple-hit” model in which hyperglycemia is only one of several concurrent insults. Insulin resistance and compensatory hyperinsulinemia directly increase renal sodium reabsorption and activate the intrarenal RAAS and sympathetic pathways, thereby amplifying the afferent arteriolar vasodilation observed in T1DM [16,24,31]. Visceral adiposity imposes an additional hemodynamic burden through the accumulation of renal sinus fat, compression of the renal medulla, and adipokine-mediated inflammation, promoting glomerular hypertrophy and hyperfiltration independently of glycemia [3,15]. Atherogenic dyslipidemia and hyperuricemia, both of which are significantly more prevalent in youth-onset T2DM than in T1DM, cause further renal injury through lipotoxic effects on podocytes, uric acid-mediated afferent arteriolopathy, and endothelial dysfunction. Moreover, elevated serum uric acid levels independently predicted both hypertension and DKD in the TODAY cohort [17,25]. The cumulative effects of these converging pathways, summarized in Table 4, plausibly explain why a given degree of hyperglycemia appears to cause substantially greater renal injury in T2DM than in T1DM.
Across several cohorts, female adolescents with T2DM have demonstrated a disproportionately higher risk of hyperfiltration and nephropathy progression than their male counterparts. This pattern has been observed less consistently in T1DM, in which female sex is more specifically associated with increased urinary albumin excretion during puberty [12,25]. Puberty itself appears to represent a period of increased vulnerability in both types of diabetes, likely because of the combined effects of activation of the growth hormone/insulin-like growth factor 1 axis, transient physiological insulin resistance, and behavioral changes affecting glycemic control. Population-level data, including those from the Gulf region, indicate that youth-onset T2DM is increasingly recognized even in settings where T1DM has traditionally predominated. Affected adolescents frequently present with obesity, dyslipidemia, and early markers of metabolic complications at diagnosis. These findings support the relevance of the multiple-hit model across diverse populations and underscore the need for region-specific surveillance programs [38,39].
Regarding evidence-based interventions and prognosis, the strongest evidence for renoprotection in youth-onset T1DM comes from intensive glycemic control. Findings from the pediatric DCCT cohort and its EDIC follow-up demonstrated that early and sustained glycemic optimization reduces the long-term risk of microalbuminuria and other microvascular complications [10,11]. RAAS blockade represents a complementary strategy. Although the AdDIT trial did not meet its prespecified primary efficacy endpoint, angiotensin-converting enzyme inhibitor therapy was associated with a 43% relative reduction in the incidence of microalbuminuria (hazard ratio, 0.57). This finding is consistent with the well-established renoprotective effects of RAAS blockade in adults and supports its consideration in adolescents with T1DM who have elevated urinary albumin excretion [26].
The ATTEMPT trial provided the first dedicated evidence that an SGLT2 inhibitor, dapagliflozin, can meaningfully reduce mGFR in adolescents and young adults with T1DM and hyperfiltration. Compared with placebo, dapagliflozin reduced mGFR by 8.8 mL/min/1.73 m2, with the greatest reductions observed among participants with the highest baseline levels of hyperfiltration [27]. This finding is consistent with the hyperfiltration pathway described above and indicates that SGLT2 inhibition may offer a targeted approach to normalizing early renal hemodynamic abnormalities in T1DM, provided that the risk of diabetic ketoacidosis is carefully mitigated. In youth-onset T2DM, the DINAMO trial evaluated empagliflozin and linagliptin in adolescents and established the feasibility of SGLT2 inhibitor-based treatment in this population, although renal outcomes were secondary endpoints [28]. Similarly, the Ellipse trial demonstrated that liraglutide improves glycemic control in adolescents with T2DM while maintaining a metabolically favorable, weight-neutral profile. Metformin has also been shown to improve insulin sensitivity and vascular health in youth with T1DM. Both findings may be relevant to long-term renal risk reduction through mechanisms that precede overt nephropathy [29,32]. Among adolescents with T2DM and severe obesity, metabolic/bariatric surgery has produced greater improvements in measures of DKD over 5 years than medical therapy alone, highlighting the central pathophysiological role of adiposity in this population [30].
Clinical implications
In clinical practice, these findings support two levels of surveillance intensity. In youth-onset T1DM, annual screening for albuminuria using the urinary albumin-to-creatinine ratio and routine blood pressure measurement should begin approximately 2–5 years after diagnosis or at the onset of puberty, whichever occurs earlier. RAAS blockade should be considered after albuminuria has been confirmed by repeat testing. In youth-onset T2DM, given the accelerated trajectory of renal injury demonstrated in TODAY/TODAY2, screening for albuminuria, hypertension, and changes in eGFR should begin at diagnosis and be repeated at least annually. A lower threshold may be appropriate for initiating RAAS blockade, considering SGLT2 inhibitors or GLP-1 receptor agonists when markers of renal injury are present, and referring adolescents with severe obesity and early DKD for evaluation for metabolic/bariatric surgery. Sustained glycemic optimization remains the cornerstone of renoprotection in both groups. However, earlier escalation to adjunctive renoprotective therapy may be warranted in T2DM because of its narrower therapeutic window.
Several limitations of the current evidence base warrant consideration and highlight important directions for future research. First, the included studies are substantially heterogeneous in terms of population selection, diabetes duration, pubertal status, eGFR equations, and outcome thresholds, complicating direct comparisons of point estimates. Furthermore, despite the size and importance of TODAY/TODAY2 and SEARCH, relatively few studies have directly compared T1DM and T2DM populations using the same study design. This limits the ability to distinguish diabetes type-specific effects from cohort-specific differences in outcome ascertainment, eGFR equations, and follow-up duration. Second, most pediatric trials evaluating renal outcomes, including ATTEMPT and AdDIT, have relatively short follow-up periods and rely on surrogate endpoints, such as albuminuria and mGFR or eGFR, rather than hard clinical outcomes, such as progression to stages 3–5 chronic kidney disease or kidney failure. Long-term follow-up of these cohorts into adulthood is therefore essential. Third, novel biomarkers, including cystatin C, renal resistive index, kidney injury molecule-1, and serum angiopoietin-2, may facilitate earlier detection of renal injury than albuminuria alone. However, these biomarkers require validation in larger, diverse, longitudinal pediatric cohorts that include both types of diabetes before they can be incorporated into routine surveillance [35,36]. Finally, given the global increase in early-onset T2DM and its disproportionate burden among socioeconomically disadvantaged and racial and ethnic minority populations, future studies should prioritize representation across diverse ethnic and geographic settings, including the Middle East and North Africa, where youth-onset T2DM is becoming increasingly prevalent [4,5,39].
Conclusion
Early renal injury, manifesting as albuminuria, hypertension, and glomerular hyperfiltration, is detectable within the first several years after the diagnosis of both youth-onset T1DM and T2DM. However, available evidence consistently indicates that renal injury develops earlier, occurs more frequently, and progresses more rapidly to overt DKD in individuals with T2DM. This accelerated progression reflects a multiple-hit pathophysiology in which the effects of hyperglycemia are compounded by insulin resistance, visceral adiposity, dyslipidemia, hyperuricemia, and chronic inflammation. These findings strongly support routine, structured renal surveillance, including blood pressure measurement, urinary albumin-to-creatinine ratio testing, and eGFR assessment, from the time of diagnosis in both groups. Increased vigilance and earlier consideration of renoprotective interventions, including RAAS blockade, SGLT2 inhibitors, GLP-1 receptor agonists, and, where appropriate, metabolic surgery, are particularly important for adolescents with T2DM, in whom the window for preventing irreversible nephron loss may be considerably narrower than that in their peers with T1DM.
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