Carbohydrates
This overview connects the biochemical understanding of carbohydrates with their clinical assessment in the laboratory
Biochemical Theory and Physiology
- Carbohydrates as Fuel: Carbohydrates, primarily glucose, are our main energy source
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Metabolic Pathways
- Glycolysis: Glucose breakdown for energy
- Gluconeogenesis: Glucose synthesis from non-carb sources
- Glycogenesis: Glucose storage as glycogen
- Glycogenolysis: Glycogen breakdown to release glucose
- Pentose Phosphate Pathway: NADPH and nucleotide precursor production
- Hormonal Control: Insulin (lowers glucose) and glucagon (raises glucose) are key regulators
- Normal State: Tight blood glucose control for consistent energy, especially for the brain
- Abnormal States: Hyper/hypoglycemia, insulin resistance, and genetic metabolic disorders
Laboratory Test Procedures
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Glucose Measurement
- Principle: Enzymatic methods like glucose oxidase or hexokinase
- Specimen is plasma, serum, or whole blood
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Glucose Tolerance Test (GTT)
- Principle: Assesses glucose clearance after a glucose load
- Serial glucose measurements at timed intervals
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Glycated Hemoglobin (HbA1c)
- Principle: Measures average glucose over 2-3 months
- Immunoassay or HPLC methods
- Whole blood specimen
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Urine Glucose
- Principle: Detects glucose in urine
- Dipstick or enzymatic methods
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Ketone Measurement
- Principle: Detects ketones in blood/urine, indicating fat breakdown
- Immunoassay or enzymatic methods
- Specialized Testing: For galactose, fructose, etc., using enzymatic or chromatographic methods
Test Result Interpretation
- Normoglycemia: Fasting 70-99 mg/dL, postprandial < 140 mg/dL
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Diabetes Diagnosis
- Fasting glucose ≥ 126 mg/dL
- 2-hour GTT glucose ≥ 200 mg/dL
- HbA1c ≥ 6.5%
- Random glucose ≥ 200 mg/dL + symptoms
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Prediabetes
- Impaired fasting glucose: 100-125 mg/dL
- Impaired glucose tolerance: 2-hour GTT 140-199 mg/dL
- HbA1c 5.7-6.4%
- Gestational Diabetes: Specific OGTT criteria
- Hypoglycemia: Glucose < 70 mg/dL
- Ketones: Positive indicates fat breakdown, as in DKA
Disease State Correlation
- Diabetes Mellitus: Hyperglycemia due to insulin issues
- Prediabetes: Increased risk of type 2 diabetes and cardiovascular disease
- Gestational Diabetes: Diabetes during pregnancy, risks for mother/baby
- Hypoglycemia: Low glucose, various causes
- Diabetic Ketoacidosis (DKA): Hyperglycemia, ketosis, acidosis (life-threatening)
- Hyperosmolar Hyperglycemic State (HHS): Extreme hyperglycemia, dehydration
- Genetic Disorders: Galactosemia, hereditary fructose intolerance, etc