Type 1 Diabetes - Symptoms

The Classic Triad

Other Common Symptoms

• Rapid weight loss - both fat and lean muscle are broken down as the body burns alternative fuels; loss of extracellular fluid also contributes
• Fatigue and weakness - cells are starved of glucose despite high blood sugar
• Blurred vision - osmotic changes swell the lens of the eye
• Dry mouth and dry or itchy skin - from dehydration
• Poor wound healing and recurrent infections - hyperglycemia impairs immune function; genital candidiasis (yeast infections) is a classic early presentation, especially in women and toilet-trained children
• Secondary enuresis (bed-wetting in a previously dry child) - a well-known presentation in pediatric T1DM
• Vague abdominal discomfort - can precede or accompany DKA

Presentation with Diabetic Ketoacidosis (DKA)

• Nausea and vomiting
• Diffuse abdominal pain
• Deep, labored breathing (Kussmaul respirations) - the body exhales CO2 to compensate for metabolic acidosis
• Fruity or "nail polish" odor on the breath - from acetone produced as a ketone
• Altered consciousness - ranging from lethargy to coma in severe cases
• Tachycardia and hypotension - from severe dehydration

Key Physical and Demographic Features

• Patients are typically lean and young (diagnosis usually before age 40, often in childhood or adolescence)
• Plasma insulin and C-peptide levels are very low or undetectable
• Pancreatic autoantibodies (anti-GAD65, IAA, anti-IA-2, anti-ZnT8) are commonly present at diagnosis
• Unlike Type 2, symptoms do not develop gradually over years - the onset is usually rapid and symptomatic

Long-Term Complications (if uncontrolled)

• Cardiovascular disease (most common cause of death)
• Retinopathy - diabetic eye disease, leading cause of blindness
• Nephropathy - kidney damage
• Peripheral neuropathy - numbness, tingling, pain in feet/hands
• Foot ulcers and serious infections
• Necrobiosis lipoidica - a characteristic skin condition (waxy, yellowish-brown plaques with violaceous borders, typically on the shins)

When to Seek Emergency Care

Type 1 vs. Type 2 Diabetes - Symptom Differences

Side-by-Side Comparison

Type 1 - Key Symptom Features

• Polyuria, polydipsia, polyphagia appear rapidly and are severe
• Rapid weight loss - both fat and lean muscle break down as alternative fuel sources
• Paradox of polyphagia + weight loss - eating a lot yet losing weight is a strong red flag for diabetes
• Diabetic ketoacidosis (DKA) may be the first sign of the disease, with nausea, vomiting, abdominal pain, Kussmaul respirations (deep, labored breathing), fruity breath odor, and altered consciousness
• Secondary enuresis in children (bed-wetting after toilet training)
• Genital candidiasis (yeast infections) from sugar-rich urine
• Blurred vision from osmotic lens swelling

Type 2 - Key Symptom Features

• Most patients are asymptomatic for years - diagnosis is commonly made incidentally on blood work
• Classic symptoms of polyuria and polydipsia only appear when blood glucose exceeds the renal reabsorption threshold (~180 mg/dL)
• Thirst and frequent urination may develop so slowly the patient barely notices
• Fatigue is the most common presenting complaint
• Recurrent infections (urinary tract, skin, yeast) from chronic hyperglycemia
• Slow wound healing
• Blurred vision, dry skin, numbness/tingling in feet can all be early or late features
• Due to the insidious onset, many Type 2 patients are first diagnosed when long-term complications are already present - retinopathy, neuropathy, or nephropathy

Shared Symptoms (Both Types)

• Polyuria and polydipsia (when glucose exceeds the renal threshold)
• Fatigue
• Blurred vision
• Recurrent infections (skin, urinary, genital)
• Slow wound healing
• Dry mouth and dry skin

A Practical Rule of Thumb

• Sudden, dramatic symptoms in a young lean person → think Type 1
• Incidentally found high glucose in an older overweight person with no symptoms → think Type 2
• Any patient with polyphagia AND weight loss simultaneously → diabetes until proven otherwise

Tests That Confirm Diabetes - and Distinguish Type 1 from Type 2

Step 1 - Confirming the Diagnosis of Diabetes (Both Types)

• Diagnosis requires 2 abnormal results (same day or two different days), OR
• A single random glucose ≥200 mg/dL with classic symptoms is sufficient on its own
• Point-of-care fingerstick glucometers and continuous glucose monitors cannot be used to diagnose diabetes - laboratory plasma glucose must confirm it

"The diagnosis of diabetes can be confirmed by the presence of two abnormal tests (fasting, 2-hour OGTT, or HbA1c) or by finding both unequivocal hyperglycemia (random plasma glucose >200 mg/dL) plus typical symptoms." - Goldman-Cecil Medicine

Step 2 - Distinguishing Type 1 from Type 2

C-Peptide (most practical differentiator)

• C-peptide is co-secreted with insulin by beta cells and reflects endogenous insulin production
• Type 1: Very low or undetectable C-peptide (beta cells destroyed)
• Type 2: Normal or elevated C-peptide (insulin is being made, but not working well)
• This is the most reliable single test to distinguish the two types

Pancreatic Autoantibodies (specific for Type 1)

• Having ≥2 autoantibodies significantly raises the probability of T1DM
• Absence of antibodies does not exclude T1DM (some antibody-negative T1DM exists)
• These tests are not for routine screening of asymptomatic people - they are used when the type is genuinely uncertain

Fasting Insulin Level

• Type 1: Absent or very low
• Type 2: Normal to high (but lower than expected for the glucose level)
• Less commonly used than C-peptide as it can be exogenously administered

HbA1c (monitoring, not typing)

• Once diabetes is diagnosed, HbA1c is used every 3-6 months to monitor glucose control over the preceding ~3 months
• Caution: HbA1c is unreliable in hemolytic anemia, hemoglobinopathies (e.g. sickle cell), uremia, or after blood transfusions - use direct glucose measurements instead
• HbA1c also varies by race (higher in Black patients at the same glucose level), though diagnostic cutoffs remain the same

Urine/Blood Ketones

• Ketonemia/ketonuria is far more prominent in Type 1 (absolute insulin deficiency enables unchecked fat breakdown)
• Blood beta-hydroxybutyrate is the preferred test (more accurate than urine ketone strips, which miss beta-hydroxybutyrate)

Summary: Test Roles at a Glance