JJamie’s results were as follows: Post Dehydration Osmolality mOsm/Kg Post DDAVP
ID: 87969 • Letter: J
Question
JJamie’s results were as follows:
Post Dehydration Osmolality mOsm/Kg
Post DDAVP Osmolality mOsm/kg
Time
Weight
Urine osmolality
Plasma osmolality
Urine
Plasma
8:00
122 lbs
200
287
9:00
121.5 lbs
200
290
10:00
120 lbs
200
298
DDAVP administered
11:00
815
290
Post-dehydration osmolality (mOsm/kg)
Post DDAVP osmolality (mOsm/kg)
Diagnosis
plasma
urine
urine
283-293
> 750
> 750
normal
> 293
< 300
< 300
nephrogenic diabetes insipidus
> 293
< 300
> 750
cranial diabetes insipidus
< 293
300-750
< 750
chronic polydipsia
< 293
300-750
< 750
partial nephrogenic DI or primary polydipsia
> 293
300-750
> 750
partial cranial DI
8. Based upon the results above, and Jamie’s medical history, and the results of the MRI: Does Jamie have Diabetes insipidus? If so—which type?
Post Dehydration Osmolality mOsm/Kg
Post DDAVP Osmolality mOsm/kg
Time
Weight
Urine osmolality
Plasma osmolality
Urine
Plasma
8:00
122 lbs
200
287
9:00
121.5 lbs
200
290
10:00
120 lbs
200
298
DDAVP administered
11:00
815
290
Explanation / Answer
Diabetes insipidus is a condition characterised by excretion of large amount of dilute urine. Diabetis insipidus can be central which is due to defective secretion of vasopressin or anti diuretic hormone (ADH) from hypothalamus or nephrogenic which is due to inability of the kidneys to respond to vasopressin. The type of diabetes insipidus can easily be differentiated with the help of water deprivation test and urinalysis.
In central or cranial diabetes insipidus, which is primarily due to defective secretion of vasopressin, the osmolality of urine and plasma becomes normal after administration of vasopressin and in case of nephrogenic diabetes insipidus, the vasopressin administration will have no effect on urine and plasma osmolality.
For Jamie, the post dehydration osmalility of urine is 200 mOsm/kg. This shows that he has diabetes insipidus. After administration of vasopressin, the urine osmolality and plasma osmolality of Jamie are 815 and 290 mOsm/kg respectively. From these results, it becomes clear that Jamie is having cranial diabetes insipidus.
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