Biochemistry Flashcards
What is normal urine output?
1 ml/kg/hr
Approx 1-2 litres per 24 hours
What is the definition of polyuria?
More than 3 litres per 24 hours
What are the causes of polydipsia/polyuria?
Neurogenic Nephrogenic Iatrogenic Metabolic Psychiatric
What investigations are helpful in the setting of polyuria?
U+Es
Glucose
Calcium
Urine and serum osmolality
How is serum osmolality calculated?
2(Na + K) + glucose + urea
What is normal serum osmolality?
275-295 mosm/kg
What is the purpose of a water function test?
To investigate the cause of polyuria to separate CDI, NDI and PP
MUST NOT BE STEROID OR THYROID DEFICIENT
How is a water deprivation test performed?
Up to 8:30: No tobacco or alcohol in 24 hours prior
Allow fluids overnight, light breakfast, no tea or coffee
8:30-4:30: No fluids, dry foods permitted, weight hourly and contact team if weight loss is more than 3% 4:30 - 8:30 pm: DDAVP 2 mcg IM at 4:30 pm and measure urine output hourly for 4 hrs
How is a water deprivation test interpreted?
Normal >1.8
Partial DI 1-1.8
Complete DI <1
What should be clinically examined when there is a suspected issue with the pituitary?
Fundoscopy - check optic disc; visual field assessment
MRI brain
What is the treatment of pituitary apoplexy?
Hormone replacement - levothyroxine, hydrocortisone, testosterone
What are the biochemical findings of addisons?
Low sodium
High potassium
Hypotensive
How is a synacthen test performed?
0900: baseline bloods for cortisol and ACTH
Give synachten - 250 mcg IM or IV
0930: repeat bloods 30 mins post-synacthen
When is a synachten test CI?
Asthma
Pregnancy
Post-pituitary surgery
What is the reference range for cortisol?
280-720
What is the classical biochem for conns?
High sodium
Low potassium
What can be given to treat conns?
Spirololactone
What are the potential causes of SIADH?
Cancer Lung disease CNS Drugs (carbamezepine, chlorpromazibe) Metabolic (hypothyroid)
How can SIADH be treated?
Treat underlying cause
Fluid restriction (500-1000ml/24hr)
Demeclocycline
Tolvaptan
What is democycline?
An antibiotic but reduces responsiveness of collecting tubule to ADH
What is tolvaptain?
A vasopressor receptor agonist
What is the investigations for an addisonian crisis?
Check random cortisol
What is the treatment of an addisonian crisis?
IV hydrocortisone 50-100 mg
IV N. Saline (Na should not increase by more than 8-12 mmol/L per 24 hr)
IV sliding scale insulin
