Diabetes complications fall into two broad categories: short-term emergencies that develop over hours to days, and long-term damage that develops over years. Short-term complications include diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), and hypoglycemia. Long-term complications include cardiovascular disease, kidney disease, eye damage, and nerve damage. Tight control prevents most of them.
Short-Term (Acute) Complications
Diabetic Ketoacidosis (DKA)
DKA is a life-threatening complication that primarily affects type 1 diabetes, though it can occur in type 2. When the body cannot use glucose for energy (usually due to severe insulin deficiency), it breaks down fat rapidly, producing acidic ketones that build up in the blood.
- Triggers: Missed insulin doses, infection, heart attack, SGLT-2 inhibitors (rare)
- Symptoms: Nausea, vomiting, abdominal pain, fruity breath, rapid breathing, confusion
- Labs: Glucose above 250 mg/dL, ketones positive, blood pH below 7.3
- Treatment: IV fluids, insulin drip, electrolyte replacement in the hospital
- Mortality: Under 1% with prompt treatment; higher in older adults
Hyperosmolar Hyperglycemic State (HHS)
HHS is the type 2 version of a severe hyperglycemic emergency. Blood sugar climbs extremely high (often above 600 mg/dL), but ketones stay low because the person still produces some insulin. HHS has a higher mortality than DKA.
- Triggers: Infection (pneumonia, UTI), stroke, heart attack, dehydration, certain medications
- Symptoms: Severe thirst, frequent urination, weakness, confusion, coma
- Labs: Glucose often 600-1,200 mg/dL, serum osmolality high, minimal ketones
- Treatment: IV fluids first, then insulin, then electrolyte correction
- Mortality: 5-20% due to advanced age and comorbidities
Hypoglycemia (Low Blood Sugar)
Hypoglycemia is the opposite problem: blood sugar drops too low, typically below 70 mg/dL. It is most common in people using insulin or sulfonylureas.
| Level | Glucose | Symptoms | Action |
|---|---|---|---|
| Level 1 (alert) | 54-69 mg/dL | Shaky, sweaty, hungry | 15g fast carbs; recheck in 15 min |
| Level 2 (serious) | Below 54 mg/dL | Confusion, weakness, slurred speech | Treat immediately; may need help |
| Level 3 (severe) | Unconscious / seizure | Cannot self-treat | Glucagon injection; call 911 |
Long-Term (Chronic) Complications
Cardiovascular Disease (CVD)
Cardiovascular disease is the single biggest threat to people with diabetes. According to the CDC, adults with diabetes are twice as likely to have heart disease or stroke as those without. About 65% of diabetes deaths are due to cardiovascular causes.
- Coronary artery disease (heart attack)
- Stroke (ischemic and hemorrhagic)
- Peripheral artery disease (leg and foot circulation problems)
- Heart failure
- Atrial fibrillation
Risk reduction focuses on three targets: A1C under 7.0%, blood pressure under 130/80 mmHg, and LDL cholesterol under 100 mg/dL (or under 70 for very high risk). Statins, ACE inhibitors, and newer drugs like SGLT-2 inhibitors and GLP-1 agonists significantly reduce events.
Kidney Disease (Diabetic Nephropathy)
Diabetes is the leading cause of kidney failure in the United States, accounting for about 47% of new cases of end-stage renal disease.
Stages of diabetic kidney disease:
- Stage 1: Kidney damage with normal filtration (GFR 90+, albumin in urine)
- Stage 2: Mild GFR decline (60-89)
- Stage 3: Moderate decline (30-59), may need medication adjustments
- Stage 4: Severe decline (15-29), nephrologist referral
- Stage 5: Kidney failure (below 15), dialysis or transplant
Annual screening with urine albumin-to-creatinine ratio and serum creatinine catches early damage. ACE inhibitors, ARBs, and SGLT-2 inhibitors slow progression. See our guide on diabetic kidney disease.
Eye Disease (Diabetic Retinopathy)
Diabetic retinopathy is the leading cause of blindness in working-age adults. Over 30% of people with diabetes have some form.
- Non-proliferative retinopathy: Microaneurysms and small hemorrhages; often no symptoms early on.
- Macular edema: Fluid leaks into the central retina; distorts vision.
- Proliferative retinopathy: New fragile vessels grow; can cause catastrophic bleeding or retinal detachment.
- Diabetic macular edema: Treated with anti-VEGF injections (Lucentis, Eylea, Avastin).
Annual dilated eye exams are non-negotiable. Diabetes also raises risk of cataracts and glaucoma.
Nerve Damage (Diabetic Neuropathy)
Up to 50% of people with diabetes develop some form of neuropathy. The four types are peripheral, autonomic, focal, and proximal. Peripheral neuropathy is by far the most common, causing numbness, tingling, and pain in feet and hands. Autonomic neuropathy can affect heart rate, digestion, and bladder function.
For a deeper dive, see our guide to neuropathy and tingling.
Foot Complications
The combination of neuropathy (lost sensation) and peripheral artery disease (poor circulation) creates a dangerous situation. About 15% of people with diabetes develop a foot ulcer, and 14-24% of those ulcers lead to amputation.
- Daily foot inspection (use a mirror or ask a partner)
- Never walk barefoot
- Wear well-fitted shoes and moisture-wicking socks
- Treat any wound aggressively — see a doctor within 24 hours
Other Long-Term Complications
| Complication | Description | Risk vs non-diabetic |
|---|---|---|
| Gum disease (periodontitis) | Inflammation and bone loss | 2-3x higher |
| Skin infections | Bacterial and fungal | 2-4x higher |
| Sleep apnea | Strongly linked to type 2 diabetes | 2x higher |
| Fatty liver (NAFLD) | Fat accumulation in the liver | 2-3x higher |
| Depression | Bidirectional relationship | 2x higher |
| Cognitive decline / dementia | Especially vascular dementia | 50-100% higher |
| Certain cancers (pancreas, liver, colon) | Modestly increased risk | 20-100% higher |
| Hearing loss | Often overlooked | 2x higher |
Prevention Framework: The ABCs Plus
Most complications are preventable or delayable with systematic management.
- A — A1C under 7.0% (personalize with your doctor)
- B — Blood pressure under 130/80 mmHg
- C — Cholesterol (LDL) under 100 mg/dL, or 70 if very high risk
- D — Do not smoke
- S — Stop by for routine screenings
The 1998 UKPDS landmark study showed that tight glucose control reduced microvascular complications by 25% in type 2 diabetes. Combined ABC control reduces complication risk by 30-50% across the board.
Annual Screening Checklist
- A1C every 3 months (if not at goal) or every 6 months (if stable)
- Dilated eye exam every year
- Urine albumin-to-creatinine ratio yearly
- Serum creatinine / eGFR yearly
- Comprehensive foot exam yearly
- Lipid panel yearly
- Dental cleaning every 6 months
- Blood pressure at every visit
- Depression screening yearly
- Immunizations: flu annually, pneumococcal, shingles (age 50+), COVID-19
For a deeper walkthrough of major complications, see our full guide on related conditions and the prediabetes 101 hub.
The Bottom Line
Diabetes complications range from acute emergencies (DKA, HHS, hypoglycemia) to long-term damage of the heart, kidneys, eyes, nerves, and feet. Cardiovascular disease is the leading cause of death, but the most common complications are neuropathy and retinopathy. Aggressive control of A1C, blood pressure, and cholesterol — combined with yearly screenings — cuts risk by 30-50%. The difference between a person with diabetes who lives a full, healthy life and one who suffers complications is almost always in the daily management.
