Biochemistry and Date handling Flashcards
sudden onset polyuria and polydipsia after severe headache?
diabetes insipidus
when does frequent drinking become abnormal?
e.g needing to get up during the night, cant go anywhere without a bottle of water, drinking 10-11 L of water a day`
signs that polyuria is abnormal?
if not drinking but still urinating a lot
older man with prostate problems
what is the normal urine output?
1-2L per 24 hrs
polyuria = >3L
name 6 groups of causes of polydipsia/polyuria?
neurogenic nephrogenic iatrogenic metabolic psychiatric other
what investigations may be useful in polyuria and polydipsia?
Us&Es glucose calcium urine serum osmolality
low urine osmolality + high urea?
high urea indicates dehydration
low urine osmolality = failure to retain water
most likely diagnosis = diabetes insipidus
test for diabetes insipidus?
water deprivation test
how do you calculate serum osmolality?
2[Na + K] + glucose + urea
what is normal serum osmolality?
275-295mosm/kg
clinical signs of dehydration?
dry skin dry mucous membranes skin not as tight generally look unwell low JVP drop in erect blood pressure
what must be considered in water deprivation test?
must not be steroid or thyroid deficit as test will be uninterpretable
how does water deprivation test determine whether diabetes insipidus is cranial or nephrogenic?
give DDAVP
if condition improves = cranial
if condition unchanged = nephrogenic
what can cause high prolactin?
tonically inhibited
drugs
something blocking the inhibitory pathway - eg. tumours
what further examinations may be done in suspected diabetes insipidus due to pituitary hypofunction?
fundoscopy - check optic disc and visual fields
MRI of brain
how is pituitary hypofunction/diabetes insipidus managed?
hormone replacement - levothyroxine - hydrocortisone - testosterone surgery if tumour
what can indicate abnormal pigmentation/tanning?
in non sun-exposed sites if not exposed to sun in hand creases in sites of trauma/scars in buccal mucosa melanoma moles etc
biochemical features of addisons disease?
low Na+
high K+
high urea
high creatinine
causes of addisons?
autoimmune iatrogenic TB cancers ischaemia
first test for addisons?
synachthen test (SST) - differentiates whether cranial or adrenal problem
when is synacthen test best performed and when is the test avoided?
early morning (9am) avoid in asthma and pregnancy and post pituitary surgery
further investigations in addisons after synacthen?
plasma ACTH
adrenals Abs
imaging
what causes increased tanning in addisons?
precursor of ACTH produced in excess to try and overcome lack of cortisol
same precursor for ACTH and MSH so results in increased ACTH and MSH
how is addisons disease managed?
oral hydrocortisone, split dosing
consider fludricortisone
sick day rules
