Give me a shortcut apt notes on difference between type 1 and type 2 diabetes Clinical complications of diabetes And lab diagnosis
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Diabetes Mellitus - Shortcut Apt Notes
PART 1: TYPE 1 vs TYPE 2 DIABETES - KEY DIFFERENCES
| Feature | Type 1 DM | Type 2 DM |
|---|---|---|
| Frequency | 5-10% of DM | 90-95% of DM |
| Age of onset | Any age; mostly children & young adults | Advancing age; can occur in children |
| Pathogenesis | Autoimmune destruction of beta cells | Insulin resistance + progressive insulin deficiency |
| Autoimmunity | YES - autoimmune | NOT autoimmune |
| C-peptide | Very low / undetectable | Detectable (but decreases over time) |
| Autoantibodies | Present: GAD65, IA-2, IAA, ZnT8 | Absent |
| Islet morphology | Insulitis (T-lymphocyte infiltration); islet reduction | Amyloid deposition in islets |
| Risk factors | Genetic, autoimmune, environmental | Obesity, sedentary lifestyle, family history, hypertension, dyslipidemia, PCOS, ethnicity |
| Insulin | Absolutely required (multiple daily injections or pump) | Often oral agents first; insulin commonly needed later |
| Symptoms at onset | Usually symptomatic | Often asymptomatic - may be diagnosed only after complications appear |
| Prevention | None known | Lifestyle (weight loss + activity); metformin, acarbose may help |
Source: Henry's Clinical Diagnosis and Management by Laboratory Methods; Robbins & Kumar Basic Pathology
PART 2: CLINICAL COMPLICATIONS OF DIABETES
Complications occur ~15-20 years after onset of hyperglycemia. Present in both T1D and T2D. Divided into:
A. MACROVASCULAR DISEASE (Large/Medium arteries)
Accelerated atherosclerosis → affects aorta, coronary, peripheral vessels
| Complication | Key Points |
|---|---|
| Myocardial Infarction | Most common cause of death in DM; almost equally common in women as in men |
| Stroke | Due to accelerated cerebral atherosclerosis |
| Peripheral vascular disease/Gangrene | Gangrene of lower extremities - 100x more common in DM |
| Hyaline arteriolosclerosis | More prevalent and severe in DM; narrows arteriolar lumen |
B. MICROVASCULAR DISEASE (Small vessels / capillaries)
Hallmark: diffuse basement membrane thickening (capillaries of skin, skeletal muscle, retina, renal glomeruli, renal medulla)
1. Diabetic Nephropathy
- Glomerular capillary basement membrane thickening
- Diffuse mesangial sclerosis (mesangial matrix increase + cell proliferation)
- Nodular glomerulosclerosis (Kimmelstiel-Wilson nodules) - pathognomonic
- Renal arteriolosclerosis
- Risk: proteinuria, progressive CKD
2. Diabetic Retinopathy
- Most feared complication; can cause blindness
- Due to microangiopathy + VEGF-driven neovascularization
3. Diabetic Neuropathy
- Peripheral symmetric neuropathy of lower extremities
- Sensory > motor involvement
- Mechanism: microangiopathy of vasa nervorum + direct axonal damage
C. MECHANISMS OF VASCULAR DAMAGE (Pathogenesis)
Three key pathways of glucotoxicity:
| Mechanism | Effect |
|---|---|
| AGE formation (Advanced Glycation End-products) | Bind RAGE → release TGF-β (BM thickening), VEGF (retinopathy), ROS, procoagulant activity, smooth muscle proliferation |
| Protein Kinase C (PKC) activation | Via DAG from glycolytic intermediates → VEGF (neovascularization), TGF-β (fibrosis/matrix deposition) |
| Polyol pathway | Glucose → sorbitol via NADPH; depletes GSH → increased oxidative stress |
Source: Robbins & Kumar Basic Pathology, pp. 749-752
PART 3: LABORATORY DIAGNOSIS OF DIABETES
ADA Diagnostic Criteria - Any ONE of the following (confirmed on 2 samples if asymptomatic):
| Test | Diagnostic Cutoff |
|---|---|
| HbA1c | ≥ 6.5% (≥48 mmol/mol) |
| Fasting Plasma Glucose (FPG) | ≥ 126 mg/dL (≥7.0 mmol/L) |
| 2-hr Plasma Glucose (OGTT) | ≥ 200 mg/dL (≥11.1 mmol/L) |
| Random Plasma Glucose + symptoms | ≥ 200 mg/dL (≥11.1 mmol/L) |
In the absence of unequivocal hyperglycemia, two abnormal results are required (same or separate samples).
Key Notes on Each Test:
HbA1c:
- Must use NGSP-certified, DCCT-standardized lab method
- Point-of-care (POC) HbA1c NOT acceptable for diagnosis
Fasting Plasma Glucose (FPG):
- Fast = no caloric intake for ≥8 hours
- Limitations: large biological variability, risk of glycolysis in tube if sample delayed
OGTT (Oral Glucose Tolerance Test):
- 75 g glucose load in adults (1.75 g/kg up to 75 g in children)
- Performed in morning after 3 days of unrestricted diet (≥150 g carbs/day)
- 10-16 hour fast; ambulatory outpatients only (bed rest impairs tolerance)
- More sensitive than FPG alone
- ~20% of OGTTs fall in non-diagnostic category; repeat on 2 separate occasions if not grossly abnormal
Prediabetes Cutoffs (for reference):
| Test | Prediabetes Range |
|---|---|
| HbA1c | 5.7% - 6.4% |
| FPG | 100-125 mg/dL (Impaired Fasting Glucose) |
| 2-hr OGTT | 140-199 mg/dL (Impaired Glucose Tolerance) |
Additional Lab Markers (Typing/Distinguishing):
| Marker | T1DM | T2DM |
|---|---|---|
| C-peptide | Very low / absent | Present (reflects endogenous insulin) |
| GAD65, IA-2, IAA, ZnT8 autoantibodies | Present | Absent |
| Urine microalbumin | Monitor for nephropathy | Monitor for nephropathy |
| Lipid profile | Usually normal | Often dyslipidemia (↑TG, ↓HDL) |
Source: Tietz Textbook of Laboratory Medicine, 7th Ed. (ADA Standards 2020); Henry's Clinical Diagnosis and Management by Laboratory Methods
Quick Memory Aid - "3 Micros of Diabetic Complications"
"RNN" - Retinopathy, Nephropathy, Neuropathy (microvascular triad)
Quick Memory Aid - Lab Diagnosis
"HFRO" - HbA1c ≥6.5%, Fasting glucose ≥126, Random ≥200 with symptoms, OGTT 2-hr ≥200
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