Glucose Challenge Test (2hours after 75gm Glucose load)

Diabetes

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Fasting Required

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Measures blood sugar levels to diagnose diabetes

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Glucose Challenge Test (2 hours after 75gm Glucose load)

Why is it done?
- Primary measure: Detects impaired glucose tolerance and gestational diabetes mellitus (GDM) by measuring blood glucose response 2 hours after a standardized 75-gram glucose load
- Screening tool: Used as the standard oral glucose tolerance test (OGTT) to evaluate glucose metabolism in non-pregnant individuals and diagnostic test for GDM in pregnant women
- Clinical indications: Diagnosis of type 2 diabetes mellitus, evaluation of glucose intolerance, assessment of metabolic syndrome, and screening during pregnancy (typically between 24-28 weeks)
- Timing: Performed in fasting state, followed by glucose challenge with 75-gram glucose drink, with blood sample collected at the 2-hour mark
- Population screening: Routine screening for pregnant women regardless of risk factors, and in non-pregnant individuals with risk factors such as obesity, family history of diabetes, or sedentary lifestyle
Normal Range
- Reference values (2-hour glucose level):
  - Normal (non-pregnant): Less than 140 mg/dL (7.8 mmol/L) - Indicates normal glucose tolerance
  - Impaired glucose tolerance: 140-199 mg/dL (7.8-11.0 mmol/L) - Borderline elevated, may warrant further testing
  - Diabetes mellitus (non-pregnant): 200 mg/dL (11.1 mmol/L) or greater - Diagnostic for diabetes mellitus
- Pregnant women (GDM screening cutoff values may vary by laboratory and clinical guidelines):
  - Normal: Less than 140 mg/dL (7.8 mmol/L) or <135 mg/dL (7.5 mmol/L) depending on protocol
  - Abnormal/Positive: 140 mg/dL (7.8 mmol/L) or greater - Requires follow-up 3-hour OGTT
- Units of measurement: mg/dL (milligrams per deciliter) or mmol/L (millimoles per liter)
Interpretation
- Normal Result (<140 mg/dL): Indicates normal glucose tolerance and metabolism. In pregnant women, this negative result rules out GDM and suggests no diabetes risk at this screening point. No further glucose testing typically needed unless risk factors change.
- Impaired Glucose Tolerance (140-199 mg/dL): Indicates impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), suggesting prediabetes. Individual has increased risk of progressing to type 2 diabetes. Lifestyle modifications and monitoring recommended. In pregnant women, requires confirmatory 3-hour OGTT for definitive GDM diagnosis.
- Elevated Result (≥200 mg/dL): In non-pregnant individuals, diagnostic for type 2 diabetes mellitus. In pregnant women, highly suggestive of GDM and typically requires confirmatory testing. Indicates significant impairment in glucose regulation and metabolic dysfunction.
- Factors affecting results:
  - Medications: Corticosteroids, diuretics, beta-blockers, and some psychiatric medications can elevate glucose levels
  - Physical and emotional stress: Stress hormones (cortisol, epinephrine) elevate blood glucose
  - Illness and infection: Acute illness, infection, or recent surgery increases glucose levels
  - Improper test administration: Incomplete glucose consumption or incorrect timing of blood draw affects accuracy
  - Pregnancy hormones: Placental hormones (human placental lactogen) increase insulin resistance during pregnancy
  - Dietary intake: Recent carbohydrate loading or inadequate fasting before test can artificially elevate results
- Clinical significance:
  - The 2-hour post-load glucose value is highly sensitive for detecting glucose tolerance abnormalities and detecting early stages of diabetes
  - Better predictor of cardiovascular disease risk and mortality than fasting glucose alone
  - Identifies individuals in prediabetic range who benefit from intensive lifestyle interventions
Associated Organs
- Primary organs involved:
  - Pancreas: Beta cells in islets of Langerhans produce insulin; impaired insulin secretion leads to elevated glucose
  - Liver: Primary site of glucose production via gluconeogenesis and glycogenolysis; affected glucose uptake in diabetes
  - Skeletal muscle: Major site of glucose uptake and utilization; insulin resistance impairs glucose uptake
  - Adipose tissue: Site of insulin action; contributes to insulin resistance, particularly with visceral obesity
- Conditions commonly associated with abnormal results:
  - Type 2 diabetes mellitus: Progressive disorder characterized by insulin resistance and beta cell dysfunction
  - Gestational diabetes mellitus (GDM): Glucose intolerance first recognized during pregnancy; affects 2-10% of pregnancies
  - Impaired fasting glucose (IFG): Fasting glucose 100-125 mg/dL; represents prediabetes
  - Impaired glucose tolerance (IGT): 2-hour glucose 140-199 mg/dL; increases diabetes and cardiovascular risk
  - Metabolic syndrome: Cluster of conditions (central obesity, dyslipidemia, hypertension, elevated glucose)
  - Polycystic ovary syndrome (PCOS): Endocrine disorder associated with insulin resistance and elevated glucose
  - Cushing's syndrome: Excess cortisol causes insulin resistance and hyperglycemia
  - Acromegaly: Growth hormone excess antagonizes insulin action
- Potential complications of abnormal results/untreated hyperglycemia:
  - Microvascular complications: Diabetic retinopathy (vision loss), nephropathy (kidney failure), neuropathy (nerve damage)
  - Macrovascular complications: Myocardial infarction, stroke, peripheral arterial disease
  - Pregnancy complications (with GDM): Preeclampsia, cesarean delivery, fetal macrosomia, neonatal hypoglycemia
  - Maternal complications: Increased risk of type 2 diabetes after pregnancy, hypertension
  - Acute complications: Hyperosmolar hyperglycemic state (HHS), diabetic ketoacidosis (DKA)
Follow-up Tests
- If 2-hour glucose is 140-199 mg/dL (borderline):
  - 3-hour oral glucose tolerance test (OGTT): Confirmatory test for GDM diagnosis in pregnant women; involves fasting and blood draws at 1, 2, and 3 hours post-glucose load
  - Fasting glucose test: Baseline glucose in non-pregnant individuals to confirm prediabetes diagnosis
  - HbA1c (glycated hemoglobin): Reflects average glucose over 2-3 months; helps confirm diagnosis and assess long-term control
- If 2-hour glucose is ≥200 mg/dL (elevated/diagnostic):
  - HbA1c: To confirm diabetes diagnosis and establish baseline glycemic control
  - Fasting glucose: Confirms elevated glucose status
  - Comprehensive metabolic panel (CMP): Assesses kidney and liver function; essential before starting diabetes medications
  - Lipid panel: Assesses cholesterol and triglycerides; essential for cardiovascular risk assessment
  - Urinalysis and urine microalbumin: Screens for diabetic nephropathy and proteinuria
  - Thyroid function tests (TSH): Screens for thyroid disorders; autoimmune disease often accompanies type 1 diabetes
- Complementary diagnostic tests:
  - C-peptide level: Assesses pancreatic beta cell function to differentiate type 1 from type 2 diabetes
  - Islet autoantibodies (GAD, IA-2, ZnT8): Identifies autoimmune diabetes (LADA - Latent Autoimmune Diabetes in Adults)
  - Fructosamine: Reflects average glucose over 2-3 weeks; useful for monitoring short-term glycemic changes
- Ongoing monitoring frequency:
  - Normal glucose tolerance: General population screening not recommended unless risk factors develop
  - Prediabetes/IGT: HbA1c every 6-12 months; annual OGTT or fasting glucose may be considered
  - Diagnosed diabetes: HbA1c every 3 months for new diagnosis or change in treatment; then quarterly to annually once stable
  - GDM: Repeat glucose testing 6-12 weeks postpartum; then annual screening for life due to 50% risk of type 2 diabetes
Fasting Required?
- Fasting Requirement: YES - Fasting is mandatory for accurate results
- Fasting duration: 8-12 hours of fasting required before the initial blood draw (fasting glucose sample)
- Dietary restrictions:
  - No food or beverages (except water) for 8-12 hours before test
  - Avoid sugary drinks, coffee with cream or sugar, alcohol, and chewing gum before the test
  - Plain water is permissible and encouraged during fasting period
- Medications to avoid or adjust:
  - Inform healthcare provider about all medications; do NOT discontinue without medical advice
  - Corticosteroids (e.g., prednisone): May raise glucose; may be continued if medically necessary but should be documented
  - Thiazide diuretics: Can elevate glucose; continue taking unless directed otherwise
  - Beta-blockers: May mask hypoglycemia symptoms; discuss with provider before testing
  - Antidiabetic medications: Continue regular diabetes medications with small amount of water unless instructed otherwise
  - Hormonal medications (birth control, HRT): Generally continue as usual unless provider advises otherwise
- Pre-test patient preparation:
  - Schedule test in early morning after overnight fast for optimal accuracy
  - Avoid strenuous physical activity for 24 hours before test; physical stress elevates glucose
  - Minimize emotional stress; stress hormones increase glucose levels
  - If ill or infected, notify healthcare provider; acute illness affects glucose levels
  - Bring photo ID and insurance information
- During test instructions:
  - Initial fasting blood draw (time 0): Baseline glucose collected before glucose challenge
  - Glucose drink consumption: Must consume 75g glucose solution completely within 5 minutes; drink may taste sweet
  - Remain seated and avoid strenuous activity during test period
  - Second blood draw at 2 hours: Exact timing critical; blood taken exactly 120 minutes after glucose drink finish
  - No food during test: Continue fasting between glucose load and 2-hour sample collection
- Post-test considerations:
  - Resume normal diet and activities after test completion
  - Mild nausea or dizziness may occur from glucose load; typically resolves quickly
  - Results typically available within 1-2 business days; provider will discuss results and next steps

How our test process works!