Biochemistry and Nutrition
Items connect metabolic pathways to bedside deficiencies, diabetes diagnosis and nutritional assessment.
Core rules
- Glycolysis yields 2 ATP and 2 pyruvate per glucose; the Krebs cycle and oxidative phosphorylation yield most ATP. Anaerobic metabolism produces lactate.
- Vitamins: thiamine (B1) deficiency causes beriberi and Wernicke encephalopathy; niacin deficiency causes pellagra; vitamin C deficiency causes scurvy; vitamin D deficiency causes rickets and osteomalacia; B12 deficiency causes macrocytic anaemia with neurological signs.
- Diabetes: fasting plasma glucose ≥7.0 mmol/L, 2-hour value ≥11.1 mmol/L on an oral glucose tolerance test, or HbA1c ≥6.5%.
- Protein-energy malnutrition: marasmus is severe wasting; kwashiorkor is oedema with low albumin and flaky skin.
Worked example
A malnourished alcoholic presents with confusion, ophthalmoplegia and ataxia. This is Wernicke encephalopathy from thiamine deficiency. Give intravenous thiamine before any glucose, because a glucose load without thiamine can precipitate or worsen the encephalopathy.
Traps
- Giving dextrose before thiamine in a malnourished patient.
- Confusing vitamin B12 and folate deficiencies, which both give macrocytosis but only B12 causes neurological signs.
- Diagnosing diabetes on a random glucose without symptoms.
- Attributing oedema in a malnourished child to renal disease rather than kwashiorkor.