PLAB 1 Review – Comprehensive Study Guide and Practice
Questions for GMC Exam 2024–2025
, Most common malignancy Small cell lung cancer
associated with SIADH
Serum sodium <135 mmol/L
Plasma osmolality <280 mosm/kg
SIADH diagnostic criteria
Urine sodium >30 mmol/L Plasma
Urine osmolality >100 mosm/kg
Co-Amoxiclav
Animal bite antibiotic
If penicillin allergic —> doxycycline + metronidazole
Normal serum osmolality275-295 mOsm/kg range
High plasma osmolality and Low urine osmolality
Diagnostic criteria Diabetes(Caused by low ADH, either deficiency [cranial DI] or
Insipidusinsensitivity to ADH [nephrogenic DI])
(Causes excessive loss of water)
1. Finding a patient with high plasma osmolality and low
urineosmolality
2. Water deprivation test
- The patient is deprived of fluids —> plasma osmolality is
measured every 4 and urine volume and osmolality every 2
hours
- The patient is then given IM desmopressin (an
Diabetes insipidus ADHanalogue) and urine volume and osmolality and plasma
investigations
osmolality is measured every 4 hours
- In a normal patient fluid restriction causes a decrease
inurine volume and increase in urine osmolality.
In px with DI urine volume remains high and osmolality low.
After desmopressin if urine volume decreases and osmolality
increases its central DI. If there is no change it's nephrogenic DI.
Medication most associated Lithium
with diabetes insipidus
Diabetes insipidus treatment Desmopressin (central); hydrochlorothiazide (nephrogenic)
EKG change most consistent Widening of the QRS complex
with hyperkalaemia
Questions for GMC Exam 2024–2025
, Most common malignancy Small cell lung cancer
associated with SIADH
Serum sodium <135 mmol/L
Plasma osmolality <280 mosm/kg
SIADH diagnostic criteria
Urine sodium >30 mmol/L Plasma
Urine osmolality >100 mosm/kg
Co-Amoxiclav
Animal bite antibiotic
If penicillin allergic —> doxycycline + metronidazole
Normal serum osmolality275-295 mOsm/kg range
High plasma osmolality and Low urine osmolality
Diagnostic criteria Diabetes(Caused by low ADH, either deficiency [cranial DI] or
Insipidusinsensitivity to ADH [nephrogenic DI])
(Causes excessive loss of water)
1. Finding a patient with high plasma osmolality and low
urineosmolality
2. Water deprivation test
- The patient is deprived of fluids —> plasma osmolality is
measured every 4 and urine volume and osmolality every 2
hours
- The patient is then given IM desmopressin (an
Diabetes insipidus ADHanalogue) and urine volume and osmolality and plasma
investigations
osmolality is measured every 4 hours
- In a normal patient fluid restriction causes a decrease
inurine volume and increase in urine osmolality.
In px with DI urine volume remains high and osmolality low.
After desmopressin if urine volume decreases and osmolality
increases its central DI. If there is no change it's nephrogenic DI.
Medication most associated Lithium
with diabetes insipidus
Diabetes insipidus treatment Desmopressin (central); hydrochlorothiazide (nephrogenic)
EKG change most consistent Widening of the QRS complex
with hyperkalaemia
