Approach to Type 2 Diabetes / Prediabetes Diagnosis and Treatment and Obesity

Overview

Type 2 diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia in which insulin resistance and relative insulin secretion deficiency play a combined role and constitutes the vast majority of all diabetes cases worldwide; its incidence is rapidly increasing in parallel with the rise in obesity prevalence. Diagnosis is made with one of four criteria: fasting plasma glucose (after at least 8 hours of fasting) 126 mg/dL or higher, 2-hour glucose in oral glucose tolerance test (OGTT) with 75 grams glucose 200 mg/dL or higher, HbA1c value 6.5% or higher, or random plasma glucose 200 mg/dL or higher in a symptomatic patient (polyuria, polydipsia, unexplained weight loss, or hyperglycemic crisis); in asymptomatic patients, the diagnosis must be confirmed by repeating the same test or positive results from two different tests.

Prediabetes is impaired fasting glucose (100-125 mg/dL), impaired glucose tolerance (OGTT 2. is defined by a fasting glucose of 140-199 mg/dL or an HbA1c range of 5.7-6.4%; according to the American Diabetes Association (ADA) 2025-2026 Standards of Care, these three tests reflect different aspects of glucose metabolism, so they do not fully replace each other, and the OGTT 2-hour value captures more prediabetes/diabetes cases compared to fasting glucose and HbA1c. In the ADA's 2023 risk score-based screening recommendation performance analysis, sensitivity was found to be 95.0% and specificity 27.1% (sensitivity 97.8% in women, 92.4% in men); this means that the screening captures most real cases but produces many false positives, so a confirmatory laboratory test is required after a positive screening.

In the pathophysiological chain, insulin resistance first develops in peripheral tissues (muscle, liver, adipose tissue), pancreatic beta cells respond to the increased demand with compensatory hyperinsulinemia, over time, as beta cell reserve is depleted, relative insulin deficiency emerges, and fasting and postprandial glucose levels rise; visceral fat accumulation, chronic low-grade inflammation, and hepatic fat accompany this process. HbA1c targets are individualized according to the patient:

6.0-6.5% may be aimed for in young adults without complications and low risk of hypoglycemia; in the general adult diabetic patient, the target is below 7%; for healthy, functional elderly patients with more than ten years life expectancy, 7.0-7.5%, elderly patients with mild-to-moderate comorbidities 7.5-8.0%, and elderly patients with advanced comorbidities or cognitive impairment who require care, more relaxed targets such as 8.0-8.5% are preferred. Obesity is classified by body mass index (BMI): under 18.5 is underweight, 18.5-24.9 is normal, 25-29.9 is overweight, and 30 and above is considered obesity; obesity itself is further divided into Stage 1 (30-34.9), Stage 2 (35-39.9), and Stage 3 (40 and above).

In patients with prediabetes, the first step approach is lifestyle modification; this change includes 5-10% weight loss, at least 150 minutes of moderate-intensity exercise per week, a Mediterranean-style diet, smoking cessation, and sleep-stress management; screening for accompanying cardiometabolic risk factors (hypertension, dyslipidemia, obesity, coronary artery disease, hepatic fat, obstructive sleep apnea syndrome) is also part of this initial assessment. Metabolic surgery should be considered as a weight and glycemic management option in individuals with a BMI of 30 kg/m² or more in a patient with type 2 diabetes (27.5 kg/m² or more in a patient of Asian descent) and who are suitable surgical candidates; this recommendation is included in the ADA 2025-2026 Standards of Care and states that surgery has beneficial effects on diabetes regardless of preoperative body mass index, but the procedure should only be performed by teams experienced in obesity-diabetes-gastrointestinal surgery, in high-volume centers and where long-term nutrition/micronutrient monitoring can be provided.

Key considerations

• Adult slow-onset autoimmune diabetes (LADA) is considered a variant of type 1 diabetes and usually occurs with a slow clinical course that mimics type 2 diabetes in the non-obese patient over the age of 30; It is distinguished by glutamic acid decarboxylase antibody (anti-GAD) positivity and low C-peptide level, the response to oral agents decreases over time, and the patient becomes insulin-dependent early on.
• Monogenic diabetes (MODY) typically begins before the age of 25, is inherited in an autosomal dominant manner, and is not associated with obesity; glucokinase (MODY2) mutation has mild, stable, and usually treatment-free hyperglycemia, while HNF1A/HNF4A mutations (MODY3, MODY1) have marked susceptibility to sulfonylurea, and the diagnosis is confirmed by genetic testing.
• Gestational diabetes mellitus is detected by a screening test performed at 24-28 weeks of pregnancy and diagnosis thresholds are determined using glucose cut-off values different from type 2 diabetes; In treatment, insulin is preferred primarily instead of oral agents.
• Chronic pancreatitis or type 3c (pancreatogenic) diabetes that develops after pancreatectomy is accompanied by signs of exocrine pancreatic insufficiency (steatorrhea, weight loss, fat-soluble vitamin deficiency) and usually tends to hypoglycemia due to impaired glucagon secretion.
• Glucocorticoid-induced (steroid-related) hyperglycemia is characterized by blood glucose elevations, especially in the afternoon and evening, in patients who are started on systemic corticosteroid therapy; It can often regress when the steroid is discontinued or its dose is reduced, but it can also reveal an underlying predisposition to type 2 diabetes.
• Secondary diabetes due to acromegaly develops as a result of increased insulin resistance in the liver and muscle tissue caused by excess growth hormone; accompanying findings such as acral enlargement, coarse facial features, and headache help distinguish it from type 2 diabetes.
• Secondary diabetes due to Cushing's syndrome occurs as a result of cortisol excess, which both increases insulin resistance and accelerates gluconeogenesis in the liver; central obesity, purple stretch marks, easy bruising, and proximal muscle weakness are the accompanying clinical clues.
• Pheochromocytoma is a rare but significant secondary cause of hyperglycemia through the effects of catecholamine excess, which both increases hepatic glucose production and suppresses insulin secretion; paroxysmal hypertension, palpitations, and sweating attacks accompany it.
• Secondary causes of obesity (hypothyroidism, Cushing's syndrome, hypogonadism, polycystic ovary syndrome, weight-gaining medications, and rare monogenic forms of obesity) must be ruled out; these causes should especially be investigated in cases of excessive obesity beginning in childhood and in treatment-resistant weight gain.

Why it matters

Drug selection is made according to HbA1c-lowering effect, risk of hypoglycemia, effect on weight, and cardiovascular/heart failure/kidney benefit. Weight-reducing agents are SGLT2 inhibitors, GLP-1 receptor agonists, and metformin; DPP-4 inhibitors and acarbose are weight-neutral; SU, glinides, pioglitazone, and insulin cause weight gain.

Agents that cause hypoglycemia are SU, glinides, and insulin. In heart failure/CKD, SGLT2 inhibitors are preferred; in atherosclerotic CVD, GLP-1 receptor agonists or SGLT2 inhibitors are preferred.

Dose adjustment according to kidney function is important: metformin should be dose-reduced at eGFR 45-60 and not used at eGFR<30; sulfonylureas should be used cautiously at eGFR 30-45 and below; glinides can be used cautiously down to eGFR 15-30; most DPP-4 inhibitors require dose adjustment in advanced kidney failure (linagliptin is an exception); SGLT2 inhibitors can be used between eGFR 15-30 for cardio-renal protection, but their glucose-lowering effect may decrease, and they should not be used at eGFR<15 or on dialysis; pioglitazone and insulin can be used at all eGFR levels (including dialysis). Insulin initiation threshold: in patients with HbA1c<9% and asymptomatic, OAD (metformin) is sufficient; insulin is preferred in HbA1c>9% with symptoms, HbA1c>10%, DKA/HHS, pregnancy, FPG>300 mg/dL, or in sepsis/MI/surgical conditions.

Patients with obesity who have a BMI >30 and have not achieved the target weight loss despite diet-exercise-behavioral changes, or patients with a BMI >27 and obesity-related comorbidities (Type two DM, HT, dyslipidemia, CAD, CVA, OSAS), are candidates for medical treatment. Before initiating GLP-1 RA, absolute contraindications (personal/family history of medullary thyroid carcinoma, history of MEN-2, known hypersensitivity to the product) should be excluded; pregnancy/breastfeeding, history of pancreatitis, severe gastroparesis, and active gallbladder disease are not absolute contraindications but are caution/warning situations requiring individual risk-benefit assessment.

In addition, CBC, kidney/liver function tests, FPG, HbA1c, lipid profile, height-weight-BMI, thyroid ultrasound (for MEN2-medullary thyroid CA), and abdominal ultrasound (for biliary/pancreatic pathologies) should be requested. Evidence for cardiovascular and renal benefit comes from large-scale randomized controlled trials: in the EMPA-REG OUTCOME study (in patients with type 2 diabetes and established cardiovascular disease), empagliflozin reduced the risk of cardiovascular death by 38%, the risk of all-cause mortality by 32%, and hospitalization for heart failure by 35%; these results led to the approval of empagliflozin, for the first time in a glucose-lowering agent, for reducing the risk of cardiovascular death.

In the LEADER study, liraglutide reduced the risk of cardiovascular death by 22%; this effect is of a different magnitude than the empagliflozin finding in EMPA-REG OUTCOME (38% reduction in cardiovascular death), but since the patient populations and follow-up durations of the two studies are different, direct comparison of absolute effects is not reliable; guidelines recommend both classes as preferred options in patients with high cardiovascular risk. In diabetic kidney disease, finerenone (a nonsteroidal mineralocorticoid receptor antagonist) reduced the risk of the kidney composite endpoint by 18% and the cardiovascular composite endpoint by 14% in the FIDELIO-DKD study; the joint consensus report of ADA and KDIGO recommends considering finerenone as an ADDITION to the current ACE inhibitor/ARB and SGLT2 inhibitor therapy in type 2 diabetic-chronic kidney disease patients with a urinary albumin/creatinine ratio of 30 mg/g or higher and serum potassium of 4.8 mmol/L or lower; this triple combination provides additional renoprotective benefits that monotherapy with renin-angiotensin system blockade cannot achieve.

In obesity treatment, the cardiovascular benefit of the GLP-1 receptor agonist class has also been shown in a non-diabetic obese population: in the SELECT study, in patients without diabetes but with established cardiovascular disease and a BMI of 27 kg/m² or higher, semaglutide 2.4 mg reduced the risk of major cardiovascular events by 20% and the average weight loss was approximately 10.2%; this finding indicates that the cardiovascular benefit of GLP-1 RA is not only dependent on glycemic control, and that obesity treatment itself can provide independent cardiovascular protection. The evidence base for individualizing glycemic targets also comes from large randomized studies: in the ACCORD study, the intensive treatment arm aiming to reduce HbA1c below 6% was terminated early because it increased the risk of all-cause mortality compared to standard treatment (HbA1c 7.0-7.9%); this result demonstrated that aggressive HbA1c targets could harm patients with longstanding diabetes, established cardiovascular disease, or high risk of hypoglycemia and provided the basis for guidelines recommending individualized, more relaxed targets according to age/comorbidities.

In contrast, the long-term follow-up data of the UKPDS study showed a reverse 'legacy effect'; in patients who received intensive glycemic control early after diagnosis, particularly those using metformin, the risk of myocardial infarction and all-cause mortality remained reduced even years after the study ended, supporting the view that early and good glycemic control at the time of diagnosis provides an unmeasurable future protection. The Look AHEAD study, on the other hand, contrary to expectations, showed that intensive lifestyle intervention in obese/overweight patients with type 2 diabetes did not significantly reduce the composite endpoint consisting of cardiovascular death, myocardial infarction, stroke, or hospitalization due to angina compared to standard care; however, in the lifestyle intervention group, improvements were observed in the risk of chronic kidney disease, blood pressure, medication use, and sleep apnea, as well as partial remission of diabetes in some patients, thus it should be accepted that although weight loss does not reduce the risk of cardiovascular events, its glycemic and microvascular benefits are sustained.

The current guideline threshold for metabolic surgery indication has also become clear: the ADA 2025-2026 Standards of Care recommend considering metabolic surgery as a weight and glycemic management option in suitable surgical candidates with BMI of 30 kg/m² or higher (27.5 kg/m² or higher in patients of Asian origin); the beneficial effect of surgery on diabetes has been shown regardless of preoperative body mass index, but the procedure must be performed in high-volume centers by interdisciplinary teams that can provide long-term nutrition/micronutrient monitoring.

Critical complications

• Diabetic nephropathy (microalbuminuria/macroalbuminuria, eGFR decline) — screening with annual urine albumin/creatinine ratio and eGFR; renoprotective treatment with ACE inhibitor/ARB and SGLT2 inhibitor.
• Diabetic retinopathy (nonproliferative/proliferative, macular edema) — at diagnosis and one dilated fundus examination per year; referral to an ophthalmologist for advanced stage laser photocoagulation or anti-VEGF treatment. [numeric values preserved: 1]
• Diabetic neuropathy (peripheral, autonomic, mononeuropathy) — annual monofilament and vibration sense examination; in symptomatic painful neuropathy, gabapentinoid/duloxetine treatment, and in autonomic neuropathy, assessment for orthostatic hypotension and gastroparesis.
• Macrovascular disease (coronary artery disease, cerebrovascular disease, peripheral arterial disease) — regular cardiovascular risk assessment, lipid and blood pressure control; GLP-1 RA/SGLT2i with proven cardiovascular benefit is preferred in high-risk patients.
• Hypoglycemia (mild-severe, hypoglycemic coma) — recognition in patients using SU/glinide/insulin (sweating, tremor, confusion, loss of consciousness) and emergency glucose/glucagon replacement; in recurrent attacks, the triggering drug should be reduced or changed.
• Diabetic foot (ulcer, infection, Charcot arthropathy, amputation risk) — prevention with annual foot examination (pulse, sensation, deformity), appropriate footwear, and patient education; urgent evaluation in case of infection/ischemia findings.
• Euglycemic diabetic ketoacidosis with SGLT2 inhibitor — should be considered when nausea-vomiting, abdominal pain, and fatigue occur even if blood glucose is normal/mildly elevated; risk increases especially preoperatively during fasting, low carbohydrate diet, severe infection or alcohol use; blood/urine ketones should be checked, the drug discontinued, and insulin and fluid replacement administered if necessary.
• Acute pancreatitis with GLP-1 RA (severe abdominal pain, high lipase) — if suspected, the drug should be stopped immediately and the patient evaluated; rare Fournier's gangrene with SGLT2 inhibitor (sudden severe pain, edema, fever in the genital/perineal region) should be considered a surgical emergency, with drug discontinuation, urgent debridement, and broad-spectrum antibiotic therapy started.
• Diabetic ketoacidosis is recognized by the triad of blood glucose level at 200 mg/dL or above, beta-hydroxybutyrate level at 3.0 mmol/L or above or urine ketone 2+ or higher, and pH below 7.3 or bicarbonate below 18 mmol/L; treatment consists of intravenous fluid replacement, insulin infusion, and electrolyte monitoring (especially potassium).
• Hyperosmolar hyperglycemic state is recognized by plasma glucose at 600 mg/dL or above, effective serum osmolality over 300 mOsm/kg (or total osmolality over 320 mOsm/kg), absence of significant ketonemia and acidosis (pH 7.3 or higher, bicarbonate 15 mmol/L or higher); approximately a quarter of patients may have a mixed presentation overlapping with diabetic ketoacidosis, and treatment consists of intensive fluid replacement and careful insulin titration.

Special considerations

• Pregnancy — the diagnosis and treatment of gestational diabetes differ from type 2 DM (screening with 75g OGTT, different glucose thresholds); insulin is preferred over oral antidiabetics, metformin can be used in some cases, but GLP-1 RA/SGLT2i are contraindicated in pregnancy.
• Elderly/frailty patients — looser HbA1c targets (7.5-8.5%) are preferred due to the risk of falls, hypoglycemia, and functional loss; agents that cause hypoglycemia (SU, insulin) should be avoided or carefully titrated.
• Kidney failure — drug selection and dose adjustment according to eGFR are mandatory (metformin contraindicated if eGFR<30, SU/glinides use with caution in advanced CKD, SGLT2i not used if eGFR<15/on dialysis); pioglitazone and insulin can be used at all eGFR levels.
• Liver failure — in advanced liver failure, metformin (risk of lactic acidosis) and pioglitazone (hepatotoxicity) should be used cautiously; insulin is generally a safe choice and the dose should be adjusted according to hypoglycemia risk.
• Childhood type 2 DM — usually associated with obesity, diagnostic criteria are similar to adults but first-line treatment is metformin and lifestyle modification; most oral agents are not approved in children, insulin and some GLP-1 RAs can be used in selected age groups.
• Patient with chronic kidney disease and albuminuria — in patients with urine albumin/creatinine ratio of 30 mg/g or above and serum potassium 4.8 mmol/L or below, addition of finerenone to ACE inhibitor/ARB and SGLT2 inhibitor should be considered according to ADA/KDIGO joint consensus; this triple combination has separately reduced kidney and cardiovascular composite endpoints.
• Patient on immunosuppressive therapy or post-organ transplant — especially calcineurin inhibitors and chronic glucocorticoid use accelerate post-transplant diabetes development; in these patients, drug selection should be made considering transplant drug interactions (especially through CYP enzymes) and rejection risk, and dose adjustments should be planned together with the nephrology/transplant team.

Follow-up plan

Screening schedule in diabetic patients: fundus examination, nephropathy screening (urine albumin/creatinine ratio, eGFR), neuropathy examination, and diabetic foot examination. In Type 1 DM, screening starts 5 years after diagnosis; in Type 2 DM, it starts at the time of diagnosis and is repeated annually.

HbA1c is measured at the time of diagnosis in both Type 1 and Type 2 DM. In uncontrolled Type 2 DM, it is repeated every 3 months; in stable patients, every 6 months.

Blood pressure is measured at the time of diagnosis in both groups and at every visit in Type 2 DM. Lipid profile is measured at the time of diagnosis in both groups and annually in Type 2 DM.

Cardiovascular risk assessment is done at the time of diagnosis and at each visit in Type 2 DM. Dental examination is recommended at the time of diagnosis and annually.

In prediabetic patients, FPG/HbA1c and diabetes screening should be done annually, and cardiovascular risk factors should be evaluated at every check-up. [numeric values preserved: 1, 1, 1, 1] Acute complications (DKA, HHS, mild/severe hypoglycemia, hypoglycemic coma) require emergency management; chronic complications should be monitored as microvascular (retinopathy/macular edema/blindness, nephropathy/albuminuria/CKD, peripheral-autonomic-mono neuropathy), macrovascular (coronary artery disease, cerebrovascular disease, peripheral artery disease), and other (cataract/glaucoma, gastroparesis, erectile dysfunction/neurogenic bladder, cardiovascular autonomic neuropathy-orthostatic hypotension).

The effectiveness of medications in obesity treatment should be regularly evaluated (e.g., if a patient on liraglutide 3mg has not achieved 5% weight loss within 3 months after reaching the target dose, the treatment should be discontinued); in patients using orlistat, SUT criteria (at least 5% of baseline weight by week 12) should be monitored. In the long term, diabetic patients should undergo a comprehensive complication screening (fundus, urine A/C ratio+eGFR, monofilament/neuropathy examination, foot examination, lipid profile) at least once a year; HbA1c should be monitored every 6 months in stable patients at target, and every 3 months in patients not at target or with therapy changes, and cardiovascular risk should be reassessed at each visit.

In patients who have undergone metabolic surgery, lifelong regular medical and behavioral support along with routine monitoring of micronutrients (iron, B12, vitamin D, calcium), nutrition, and metabolic status are required; if this monitoring is not maintained, the risk of postoperative nutritional deficiencies and weight regain increases.