Biochemistry Tutorial Flashcards
what is polyuria
> 3 litres of urine in 24 hours
what is normal urine output
1-2 litres per 24 hours
what are the causes of polydipsia/ polyuria
neurogenic nephrogenic iatrogenic metabolic psychiatric pregnancy
(e.g. cranial and nephrogenic diabetes insipidus)
what is polydipsia
excessive thirst
what investigations would you do in polyuria
U+E, glucose, calcium, urine and serum osmolality
what would polyuria with high sodium, high urea and low urine osmolality suggest
dehydration (likely to be diabetes insipidus)
when is a frontal headache associated with polyuria
cranial diabetes insipidus caused
how do you calcultae serum omsolality
2(Na + K) + glucose + urea
what is normal serum osmolality
275-295 mosm/kg
what further tests could you do to prove cranial diabetes insipidus
water deprivation test, pituitary bloods, imaging, 9am cortisol
what does a water deprivation test separate
cranial DI, nephrogenic DI, posterior pituitary function
how do you do a water deprivation test
stop water for 8 hours then give DDAVP (desmopressin) which should act on kidneys to reduce flow of urine
if normal urine osmolality will stay the same (dehydrated)
if partial may start low/ normal and then get to normal level (concentrated)
if cranial will start low (dilute) and then get normal (concentrated)
if nephrogenic will start low (dilute) and stay low (unaffected by desmopressin)
what is causing the problem in cranial and nephrogenic DI
cranial pituitary not producing ADH
nephrogenic kidneys not responding to ADH
what is this: 43y old woman with a recent history of weight loss, tiredness and general debility. She is underweight and has noticed increased tanning following a recent holiday. Routine electrolytes are as follows: Na 124mmol/l (hypo) K 5.4 mmol/l (hyper) Urea 8.9mmol/l Creatinine 100umol/l
addisons
what are the usually biochem markers of addisons
low Na, high K, high urea, high creatinine
what test can you do in addisons
synacthen
what is addisons
primary adrenal insufficiency
why do you not get tanning in adrenal insufficiency secondary to the pituitary
as ACTH is not in excess
what is haemoconcentrated dilute urine
when signs of dehydration but urine is dilute- seen in DI
when should you avoid synthacten testing
asthma, pregnancy, post pituitary surgery
what else do you measure in addisons
ACTH levels to determine source of insufficiency
what are you lacking in addisons
cortisol (and sometimes aldosterone)
how do you treat addisons diseaase
oral hydrocortisone, split dosing consider fludricortisone (mineralocorticoid)
name the disease:
low sodium
high potassium
high urea
addisons
what are the three H’s of addisons
hypotension, hyperkalaemia, hyponatraemia
name the disease:
normal sodium
low potassium
normal urea
conns (adrenal adenoma) causes hypokalaemia (excess production of aldosterone)
when is urea high
when dehydrated (and lots of other things)
name the disease:
low sodium
low potassium
low urea
SIADH- hyponatraemia secondary to impaired free water excretion (too much ADH)
what treatment do you give in conns
spironolactone (aldosterone antagonist)
or remove tumour
what are the causes of SIADH
cancer, lung disease, CNS, drugs, metabolic (hypothyroid)
how do you treat SIADH
treat underlying cause
fluid restriction
demeclocycline
tolvaptan
what is demeclocycline
an antiboitic that reduces responsiveness of collecting tubule to ADH
what is tolvaptan
a vasopressor receptor agonist
what is addisons with a low BP
addisonian crisis
what investigation for addisonian crisis
random cortisol (dont wait for result)
what is the treatment for an addisons crisis
IV hydrocortisone 50-100mg immediatley
IV N. saline (should not be increased by more than 8-12 mmol/L per 24 hour)
IV sliding scale insulin
what should bicarb be in DKA
under 15 (bicarb is alkaline, low will created acidosis)
