Diabetes Insipidus Flashcards
First step in evaluation of hypotonic polyuria
Confirm polyuria
>50ml/kg/24H or >3-4L/day
Next step after polyuria is confirmed
Measure urine osmolality
If <800mOsm/kg, hypotonic polyuria confirmed
Next step after hypotonic polyuria is confirmed
Measure serum sodium and plasma osmolality
How do you diagnose primary polydipsia before WDT?
Low normal serum Na and plasma osmolality <280 mOsm/kg
If normal or high serum sodium and osmolality, what is the next step?
Water deprivation test or copeptin tests
Water deprivation test urine osmolality >800 mOsm/kg before DDAVP
Primary polydipsia
WDT osmolality <300 before DDAVP or 300-800
Proceed with DDAVP
Complete central DI after DDAVP
Urine osm < 300 and >50% increase after DDAVP
Complete nephrogenic DI after DDAVP
Urine osm <300 or <50% increase
If Urine osmolality 300-800 after DDAVP and <50% increase
Therapeutic trial with DDAVP
Interpretation of therapeutic trial with DDAVP
Resolution of symptoms - partial central DI
No change in symptoms - partial nephrogenic DI
Decreased plasma osmolality - primary polydipsia
Baseline copeptin levels
< 2.6 pmol/L - Central DI
>21.4 pmol/L - Nephrogenic DI
Inbetween - do hypertonic saline infusion test
Copeptin after hypertonic saline
> 4.9 - primary polydipsia
< 4.9 - central DI (either complete or partial)
Water deprivation test points to remember
Patient must have normal/replaced thyroid and adrenal reserve.
Stop the test if the patient loses >3% of body weight.
WDT normal response
Urine osmolality rises and urine volume falls with water deprivation.
Urine:plasma osmolality should be >2 at the end of the test.
Plasma osmolality rises but remains <295 mosmol/kg
Vasopressin receptors - V1
Blood vessels, platelets, liver - vasoconstriction and platelet aggregation
Vasopressin receptors - V2
Kidney collecting ducts - water retention
Vasopressin receptors - V3
Anterior pituitary - ACTH secretion
Short and long term treatment of central DI
DDAVP for both terms
Short term treatment of nephrogenic DI
Hydration, identify and eliminate the cause
Long term treatment of NDI
- Thiazides
- NSAID - indomethacin
- Amiloride for lithium induced NDI
Non pharmocological management of NDI
Low sodium and low protein diet
Dose of DDAVP in central DI
Nasal - 5 to 100mcg/day
Oral - 100-1000mcg/day
Parenteral: 0.1-2 mcg/day
