Biochemistry Tutorial

Question 1

what is polyuria

Answer 1

> 3 litres of urine in 24 hours

Question 2

what is normal urine output

Answer 2

1-2 litres per 24 hours

Question 3

what are the causes of polydipsia/ polyuria

Answer 3

neurogenic
nephrogenic 
iatrogenic 
metabolic 
psychiatric 
pregnancy

(e.g. cranial and nephrogenic diabetes insipidus)

Question 4

what is polydipsia

Answer 4

excessive thirst

Question 5

what investigations would you do in polyuria

Answer 5

U+E, glucose, calcium, urine and serum osmolality

Question 6

what would polyuria with high sodium, high urea and low urine osmolality suggest

Answer 6

dehydration (likely to be diabetes insipidus)

Question 7

when is a frontal headache associated with polyuria

Answer 7

cranial diabetes insipidus caused

Question 8

how do you calcultae serum omsolality

Answer 8

2(Na + K) + glucose + urea

Question 9

what is normal serum osmolality

Answer 9

275-295 mosm/kg

Question 10

what further tests could you do to prove cranial diabetes insipidus

Answer 10

water deprivation test, pituitary bloods, imaging, 9am cortisol

Question 11

what does a water deprivation test separate

Answer 11

cranial DI, nephrogenic DI, posterior pituitary function

Question 12

how do you do a water deprivation test

Answer 12

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)

Question 13

what is causing the problem in cranial and nephrogenic DI

Answer 13

cranial pituitary not producing ADH

nephrogenic kidneys not responding to ADH

Question 14

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

Answer 14

addisons

Question 15

what are the usually biochem markers of addisons

Answer 15

low Na, high K, high urea, high creatinine

Question 16

what test can you do in addisons

Answer 16

synacthen

Question 17

what is addisons

Answer 17

primary adrenal insufficiency

Question 18

why do you not get tanning in adrenal insufficiency secondary to the pituitary

Answer 18

as ACTH is not in excess

Question 19

what is haemoconcentrated dilute urine

Answer 19

when signs of dehydration but urine is dilute- seen in DI

Question 20

when should you avoid synthacten testing

Answer 20

asthma, pregnancy, post pituitary surgery

Question 21

what else do you measure in addisons

Answer 21

ACTH levels to determine source of insufficiency

Question 22

what are you lacking in addisons

Answer 22

cortisol (and sometimes aldosterone)

Question 23

how do you treat addisons diseaase

Answer 23

oral hydrocortisone, split dosing 
consider fludricortisone (mineralocorticoid)

Question 24

name the disease:
low sodium
high potassium
high urea

Answer 24

addisons

Question 25

what are the three H’s of addisons

Answer 25

hypotension, hyperkalaemia, hyponatraemia

Question 26

name the disease:
normal sodium
low potassium
normal urea

Answer 26

conns (adrenal adenoma) causes hypokalaemia (excess production of aldosterone)

Question 27

when is urea high

Answer 27

when dehydrated (and lots of other things)

Question 28

name the disease:
low sodium
low potassium
low urea

Answer 28

SIADH- hyponatraemia secondary to impaired free water excretion (too much ADH)

Question 29

what treatment do you give in conns

Answer 29

spironolactone (aldosterone antagonist)

or remove tumour

Question 30

what are the causes of SIADH

Answer 30

cancer, lung disease, CNS, drugs, metabolic (hypothyroid)

Question 31

how do you treat SIADH

Answer 31

treat underlying cause
fluid restriction
demeclocycline
tolvaptan

Question 32

what is demeclocycline

Answer 32

an antiboitic that reduces responsiveness of collecting tubule to ADH

Question 33

what is tolvaptan

Answer 33

a vasopressor receptor agonist

Question 34

what is addisons with a low BP

Answer 34

addisonian crisis

Question 35

what investigation for addisonian crisis

Answer 35

random cortisol (dont wait for result)

Question 36

what is the treatment for an addisons crisis

Answer 36

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

Question 37

what should bicarb be in DKA

Answer 37

under 15
(bicarb is alkaline, low will created acidosis)