Basic Medical Sciences
Basic Medical Sciences tests anatomy, physiology, pathology, biochemistry, and microbiology as applied to clinical questions. Expect acid-base, electrolyte, and anemia reasoning rather than isolated facts.
Core rules
- Calculate anion gap: Na − (Cl + HCO3); normal is about 8–12 mEq/L.
- Metabolic acidosis with respiratory compensation lowers PaCO2; compensation is not complete, so pH remains abnormal.
- Iron deficiency is microcytic with low ferritin; anemia of chronic disease is normocytic or microcytic with normal or high ferritin.
- Gram-positive cocci in clusters suggest Staphylococcus aureus; in chains, Streptococcus.
Worked example
ABG: pH 7.25, PaCO2 30 mmHg, HCO3 14 mEq/L. The primary disorder is metabolic acidosis; PaCO2 is low as respiratory compensation. Calculate the anion gap. If it is high, consider lactate, ketones, renal failure, and toxins. If normal, assess diarrhea and renal tubular acidosis. Do not call it respiratory alkalosis because PaCO2 is low.
Traps
- Interpreting a low PaCO2 as the primary disorder when bicarbonate is also low.
- Forgetting to calculate the anion gap.
- Using ferritin alone without inflammation context.
- Mixing up Staphylococcus and Streptococcus morphology.