Basic and clinical sciences applied to the specialty
Domain 1 - Basic and clinical sciences applied to the specialty
This domain tests whether you can use physiology, pathology, pharmacology, microbiology, and genetics to explain and predict clinical events, rather than recall isolated facts. Questions often present a patient whose presentation only makes sense through a mechanism.
Core rules
- Reason from mechanism to management: identify the disturbed process (preload, afterload, oncotic pressure, receptor signalling, microbial virulence) before choosing therapy.
- Adjust pharmacokinetics for organ function: renal clearance affects dosing of renally eliminated drugs; hepatic impairment affects first-pass metabolism and protein binding.
- Link pathology to expected test results, and distinguish the expected abnormality from a complication.
- Consider development and ageing: children and older adults differ in body composition, clearance, and compensatory reserve.
Worked example
A 58-year-old with cirrhosis and ascites presents with fever and generalized abdominal pain. Ascitic fluid PMN count is 420/mm³. The mechanism-based reasoning is spontaneous bacterial peritonitis: translocation of gut organisms into ascitic fluid with low opsonic activity. Treatment is IV ceftriaxone; albumin is added because it reduces renal impairment and mortality, probably by improving effective circulating volume and oncotic pressure. This is mechanism plus evidence, not simply "give antibiotics".
Traps
- Choosing a drug by name without checking hepatic or renal dose adjustment.
- Treating a laboratory value without asking whether it is expected for the disease.
- Forgetting that older patients may lack fever or leucocytosis.